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Bases Químicas de la Vida. Clase Teórica IBH Facimed. — Transcript

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0:01Good morning.
0:04We are going to start the biology
0:08theory session and it's my turn to give
0:12it today. The different theory sessions
0:14will be given by the various professors
0:16of the course. Yes, we are going to
0:19take turns regarding the theory
0:21sessions. Uh, my name is Federico
0:24Bolzik. I am in the Wednesday afternoon
0:27group, if I'm not mistaken, in group
0:30number five. Yes. Wednesday afternoon,
0:33whe-? Friday, it doesn't matter.
0:35Wednesday afternoon. Yes. Uh, and today
0:39it fell to me to prepare and give you
0:41the first theory session of the course.
0:45Remember that theory sessions are not
0:47mandatory. Yes, we are being filmed and
0:51this will later be on the platform. Yes
0:56, so that those who don't come to class
0:58can watch it and repeat it as many
1:00times as they want, including you as
1:02well. Yes, the first theory session
1:09probably won't have many new terms or
1:11concepts. Yes, we are going to talk
1:15about the chemical bases of life. You
1:18won't see this topic in class this week
1:20, but rather next week. Yes, this
1:23theory session will be uploaded,
1:25probably tomorrow or the day after, so
1:27you have the chance to watch it and
1:29wait for it calmly on Saturday night.
1:32Good morning, night. You arrived late.
1:37Uh, to talk about uh this topic we are
1:43going to focus a little bit, it's not
1:51fully visible, but on the central
1:52structure that allows giving uh form to
1:54matter. Yes. Uh, you surely saw this in
2:02chemistry. Yes. Yes, some actually just
2:05came from chemistry class. I teach
2:09chemistry here too, so I come from the
2:11Monday morning chemistry group, so you
2:13will surely see and repeat some of the
2:15concepts we were seeing today and in
2:17previous classes, yes? And those who
2:21have chemistry tomorrow, the day after,
2:23and the rest of the days will surely
2:25see some of these things again. The
2:27atom. Everyone already knows how the
2:29atom is constituted. Yes. A nucleus and
2:32a shell. In the nucleus, what do we
2:34have?
2:35Protons and neutrons. And what charge
2:37does the nucleus have?
2:39Positive. An atom. Yes, as it appears
2:42in the periodic table, does it have a
2:44charge?
2:46No. Why?
2:47Because it is neutral. Why is it
2:49neutral?
2:51Because it has the same number of
2:53electrons as protons. And is the number
2:55of neutrons the same? No,
2:57no,
2:57no. Why?
2:58Because it is the difference between
3:00the mass number and the atomic number.
3:02Right, that is the consequence. The
3:04number of protons is not necessarily
3:06the same as the number of neutrons. Two
3:09elements that have the same atomic
3:11number but a different mass number,
3:12what are they called?
3:14Isotope.
3:14Isotope. Very good. So, we have an atom
3:19, right? Which has protons and neutrons
3:22in its nucleus. In the outer shell, it
3:26has electrons. Electrons are not placed
3:29randomly; they are located in orbitals.
3:33And everything you were looking at
3:34regarding the atomic theory, right? You
3:41saw Dalton, Bohr, yes, you saw
3:43different types of atomic theories, and
3:45the modern one, the current one that we
3:48are applying, is the one that talks
3:50about different orbitals. Right?
3:56Electrons are found in different
3:58orbitals, right? The number of orbitals
4:01increases as the periods increase in
4:03the periodic table. There is a direct
4:05relationship between orbitals and the
4:07period. But what we are going to be
4:12interested in here is not the total
4:14number of electrons, but the number of
4:16electrons in the outermost shell. Why?
4:21Because that will allow us to identify
4:23the chemical bonds they can have. Does
4:25everyone know what the octet rule is?
4:27Yes. Yes.
4:28What does the octet rule mean, or what
4:31does it say in general terms?
4:33That for an atom to be stable, it must
4:35have eight electrons in its last orbit.
4:37Good. Exactly. For an atom to be stable
4:39, it must have eight electrons in its
4:41last orbit. The external electronic
4:45configuration refers to the atoms of
4:47the outermost layer. Yes, precisely the
4:50external electronic configuration.
4:53Those in the furthest level, right? It
4:56is what will interest us most when
4:57talking about chemical bonds. Within
5:02chemical bonds, we will be mainly
5:04interested in the covalent bond. Yes,
5:07the ionic bond a little less, and we
5:09won't give much importance to the
5:11metallic one among the elements we will
5:17see most because we are talking about
5:19biology, right? So, biological elements
5:22are made up of a series of particular
5:25atoms or mainly by some types of atoms.
5:30And in the human body, we can find a
5:32lot of different atoms forming
5:33different types of molecules, but
5:35mainly we will find those in light
5:37yellow, right? Like carbon, nitrogen,
5:43oxygen, phosphorus, sulfur, and
5:45hydrogen. Yes, in a smaller proportion
5:49we will find some elements that, if you
5:52look closely at their distribution, are
5:54both metallic and non-metallic. Yes, we
5:58will find chlorine and silicon as
6:00non-metals. As metals, we will find
6:05magnesium, sodium, potassium, calcium,
6:08manganese, iron, cobalt, yes, copper,
6:11zinc, as part of the elements that will
6:14mainly be present as ions in the body's
6:17physiological solution. We will find
6:21them as ions and, as we move through
6:23the year, especially in the second part
6:25where we look more at physiology, right
6:27? The second part of the year, when we
6:31look at action potentials, the nervous
6:33system, students who are retaking the
6:36course surely remember some of these
6:38ions, especially calcium, especially
6:40potassium, and sodium. Right? So, these
6:47will be more or less the elements we
6:49will focus on, mainly when we talk
6:51about organic compounds, when we talk
6:53about macromolecules. Yes, in most
7:01living beings we will find this type of
7:03atom, yes? Carbon, hydrogen, oxygen,
7:07and nitrogen. Yes, CHON. Carbon,
7:10hydrogen, oxygen, nitrogen, so you
7:12remember, a mnemonic rule: CHON. The
7:18most abundant ones we will have. They
7:20make up, notice, 99%of the mass of a
7:23living being. Yes, these four elements;
7:27we have others too, yes? Like, for
7:31example, phosphorus or sulfur, which we
7:33mentioned before as well. Those are in
7:37smaller proportions, but these are the
7:39main ones. Now, you have already seen
7:42this slide, but which atom would you
7:44have thought was the most abundant in
7:46the body?
7:50Carbon. Yes. Anyone would think that
7:53the most abundant atom is carbon. Yes.
7:56Because the whole body, all
7:58macromolecules, are based on carbon
8:00bonds, yes? On the capacity carbon has
8:03to bond with different types of
8:05elements. Carbon is found in group four
8:07of the periodic table, in period two.
8:10Yes? So, that gives it the capacity to
8:13bond to four molecules—sorry, to four
8:16atoms—that can be different. So,
8:19anyone would think that carbon is the
8:22central base. I mean, carbon is the
8:24central base, but it is not the one in
8:26the highest proportion. As I just said,
8:29carbon can bond to four more elements.
8:33Yes, in most cases, those elements are
8:35hydrogens. Yes? We will see some
8:40macromolecule structures a little later
8:42where you will clearly see the
8:44structure, especially of lipids, yes?
8:46Which are hydrocarbon chains, right?
8:49Carbon, carbon, carbon, and the sides
8:52have hydrogen. So, this means that for
8:55every carbon molecule, generally, there
8:57are two hydrogen molecules. Right? Also
9:00, the body, how is it formed? Mainly,
9:03how is it constituted?
9:05By water. And water, what is the
9:07formula for water?
9:08H2O. So, we have twice as much hydrogen
9:11as oxygen. Right? So, hydrogen, notice
9:15that it makes up 63%of the elements,
9:19right, that we have in our body. Then,
9:23oxygen, carbon, nitrogen, and the rest
9:26make up approximately 1%. The CHONs, in
9:33this case we add phosphate, right, but
9:35more or less we are talking about or
9:38referring to the same thing. Mind you,
9:40it's not the Frigor "Chom" brand. Yes.
9:43For those who are hungry at this hour
9:48it's getting a bit late. Uh, these
9:50chemical elements are part of organic
9:52compounds and inorganic compounds.
9:56Right? We will have, for example, water
9:59, mineral salts, right? As inorganic
10:02compounds. When it comes to organic
10:05compounds, we will find carbohydrates,
10:07which are sugars, lipids, proteins, and
10:10nucleic acids. DNA and RNA. In other
10:15words, those five compounds located
10:18there, right, above, are part of all
10:20the macromolecules and many of the
10:22inorganic substances we will find in
10:24the body. This is what allows, the
10:28combination of both, for the cell to be
10:30a functional structure, right? And to
10:33have life. Yes. The cell is the
10:37smallest functional, uh, living unit.
10:41Yes. The smallest, uh, living being is
10:44made up of a single cell. We talked
10:51about bonds. We said we were going to
10:53mention the bonds. Yes. To talk about
10:58bonds, notice that I made a distinction
11:00for bonds between molecules. Yes, bonds
11:05that form biomolecules. All the
11:11elements I mentioned before, right?
11:13Those that form CHON or CHOM are what
11:15type of element on the periodic table?
11:19Non-metals. If they are non-metals,
11:21what type of bond do they form with
11:22each other?
11:23Covalent. How do two elements or two,
11:27uh, molecules that have a covalent bond
11:30join?
11:33They share electrons. Those are the
11:35atoms. Now, if I have two water
11:37molecules, how do they attract and join
11:39each other?
11:41By what type of forces?
11:45Dipole. Dipole, yes, but it is mainly
11:48called a hydrogen bond. But now we are
11:52talking about two water molecules. So,
11:54we are talking about intermolecular
11:56bonds, right? Between molecules. When
12:02we talk about these bonds between
12:04molecules, we absolutely have to keep
12:06electronegativity in mind. Yes, last
12:11week in chemistry we were looking at
12:13the periodic table, and you surely
12:15looked at atomic radius, ionic radius,
12:17and the electronegativity of elements.
12:23And this is more or less an example of
12:25how electronegativity varies across the
12:27periods and groups of the periodic
12:29table. Electronegativity increases from
12:33left to right and from bottom to top.
12:36So, what is the most electronegative
12:38element in the periodic table that can
12:40form bonds?
12:41Fluorine.
12:42Fluorine. But helium is higher up. Why
12:45isn't it the most electronegative?
12:48Because helium is a noble gas. Yes. Its
12:51outermost shell, the valence shell, is
12:54full; it satisfies the octet, right? So
12:57, it has no capacity to bond with
13:00another atom. Right? So, the most
13:04electronegative element in the periodic
13:06table is fluorine and the least is
13:08francium. Right? So, you all mentioned
13:15that water can bind through a
13:16particular type of force. What was it?
13:19Hydrogen bonding. And what are the
13:21characteristics of this hydrogen bond?
13:23Between which elements does it occur?
13:25The most electronegative elements on
13:26the periodic table.
13:27The most electronegative elements on
13:29the periodic table. And who are they?
13:33Fluorine, oxygen, and nitrogen. Yes,
13:35they are the three most electronegative
13:37elements on the periodic table. And
13:39since it's a hydrogen bond, what else
13:41must these elements have?
13:43Hydrogen. Right? So, hydrogen bonded
13:46with fluorine, oxygen, or nitrogen
13:48allows for the joining of molecules,
13:51right, by means of this type of
13:53hydrogen bond. Uh, well, we aren't
13:58going to spend much time on this. Yes.
14:00But we have ionic, covalent, and
14:03metallic bonds, right, broadly speaking
14:05. We are going to focus mainly on the
14:10compounds or molecules that are formed
14:12by covalent bonds, and you will develop
14:15this a bit more in chemistry. Yes. This
14:22too, what is the type of bond like?
14:28Remember that in ionic bonds, what
14:30happens is one element transfers an
14:32electron to another, at least. Right?
14:36Now, if an element loses an electron,
14:38what charge does it end up with?
14:40Positive.
14:41Positive. And what do we call it?
14:43Cation. And if an element accepts an
14:45electron,
14:46Anion. And what charge does it end up
14:48with?
14:48Negative.
14:49Negative. So, if one element gives and
14:51one element accepts, right? We're
14:53talking about two different ions. Right
14:56? On the periodic table, what kind of
14:58elements give electrons?
15:02Metals are elements with low
15:04electronegativity, so they give up
15:06protons—I mean, electrons. Nonmetals
15:10accept electrons. So, in the case of an
15:15ionic bond, what happens is the metal
15:17always gives up electrons and the
15:19nonmetal always accepts them. Thus, the
15:25metal ends up with a positive charge
15:27and the nonmetal with a negative charge
15:29. What kind of attraction occurs
15:31between them?
15:35Ionic. Yes. An element with a positive
15:38charge and an element with a negative
15:39charge attract each other. Opposites
15:41attract, right? Careful, let's not take
15:44it to the extreme, but opposites
15:46attract. So, a positive charge, a
15:48negative charge, ionic bond, a metal
15:51and a nonmetal. Right? So far, so good.
15:55Good. A covalent bond occurs between
15:58two metals—sorry, between two
16:00nonmetals. Since nonmetals tend to
16:05accept electrons, right? It will be
16:10very difficult for one to donate or
16:12give them away. So the solution they
16:14found was to share them. You take them
16:17for a while, I'll take them for a while
16:19. Right? And that creates the covalent
16:22bond. Nonmetallic elements join
16:26together through covalent bonds because
16:28they share electrons. Right? This makes
16:35them highly stable because they are
16:37completing the octet, right, and
16:38bonding thanks to sharing, yes, with
16:41other atoms. Here we have, for example,
16:47the formation of methane with the
16:48carbon atom. Notice, four electrons in
16:51the outermost shell, four hydrogen
16:53atoms that each have one electron in
16:56the outermost shell. So, it's not
17:01chemistry, eh, but it's similar.
17:07The chemistry teacher, the head of the
17:09chemistry department, is right there
17:11behind me checking that I’m not
17:12giving a real chemistry lecture. Well,
17:16so notice that the carbon shares, it
17:20has 1, 2, 3, 4, 5, 6, 7, 8 electrons.
17:25Right? And the hydrogens have 1, 2; 1,
17:282; 1, 2; 1, 2. We mentioned the octet
17:32rule, but the octet rule refers to
17:34eight electrons in the outermost shell.
17:37There are two exceptions, which are
17:39hydrogen and helium. Yes, those two
17:43elements need to complete two electrons
17:45in the outermost shell. Yes. Within
17:54intermolecular forces, these elements,
17:57these molecules that are joined by
17:59covalent bonds, join and interact with
18:01each other thanks to van der Waals
18:03forces. Yes, two molecules. Yes, two
18:10molecules that have covalent bonds join
18:13each other through van der Waals forces
18:15. Yes. Two water molecules join each
18:19other through van der Waals forces. Two
18:22glucose molecules join each other
18:24through van der Waals forces. Yes. Now,
18:29within the structure of glucose, the
18:31atoms that form glucose are joined by
18:37covalent bonds. Yes, definitely, right?
18:41Each of the atoms that forms glucose
18:43joins with another atom to form glucose
18:45through covalent bonds. Two glucose
18:48molecules join each other through van
18:50der Waals forces. Within van der Waals
18:53forces, we have different types of
18:55forces. Yes. And the weakest of all,
18:58the London dispersion forces, you will
19:00see those in chemistry this week. We
19:04have dipole-induced dipole, yes, we
19:07have dipole-dipole forces, or permanent
19:10dipole-dipole as well. And as an
19:14exception to these dipole-dipole forces
19:17, we have hydrogen bond forces. Right?
19:21In other words, within dipole-dipole
19:23forces, we have hydrogen bond forces.
19:26Is that understood? Good. We already
19:33mentioned what a hydrogen bond force is
19:35like, what characteristics it must have
19:37. So, let's talk a little bit about
19:42water itself. Why do we talk about
19:46water? Because water is the medium
19:48where most chemical reactions in the
19:50body occur. We said that between 60 and
19:5470%of the body is made up of water. The
19:58cell is made up of water. If there is
20:01no water, the cell dies. Yes. Not just
20:04water, but there must also be a certain
20:06ratio of solutes so that nothing
20:08happens to the cell. Right? So, water
20:12makes up between 60 or 70%of body
20:15weight. Yes, it is the place where many
20:19of the body's chemical reactions occur.
20:23It acts as a lubricant. Also, it is
20:28also associated with polarity. Water is
20:31a polar molecule. Yes, remember that
20:37oxygen is much more electronegative
20:39than hydrogen and oxygen has leftover
20:41electrons to share, meaning it has a
20:43pair of free electrons. That generates
20:50a difference in charges between the
20:52oxygen and the hydrogen that we call
20:54charge density. And so the oxygen is
20:58left with a negative charge density and
21:00the hydrogen with a positive charge
21:02density, and that generates a dipole.
21:06Right? Now, that force is so high that
21:10it stops being called dipole-dipole and
21:12is called a hydrogen bond. That makes
21:15water a polar molecule because it has a
21:17positive charge density on one side and
21:19a negative charge density on the other.
21:22Watch out, don't get confused; charge
21:24density is not net charge. Yes, the
21:28molecule is neutral, it doesn't have
21:30net positive or negative charges, it
21:32has different charge densities. In
21:36other words, the electrons are more
21:37displaced to one side of the molecule
21:39than the other. Yes, but that doesn't
21:42mean that one keeps them forever and
21:44the other, or that one donates them and
21:45the other loses them. Yes. Or one
21:48donates them and the other accepts them
21:49. Yes. They share them, but one keeps
21:52them in its orbit for longer. Yes, it
21:56has a high heat capacity. Yes, this
22:00refers to the capacity it has to
22:02contain water, to contain heat. Water
22:06has different, it has a melting point,
22:08a boiling point. As the temperature
22:10increases, it can go from one state to
22:12another. This capacity it has to bond
22:16through hydrogen bridges gives it the
22:18ability to have high melting and
22:20boiling points. Yes, water boils at 100
22:25degrees Celsius, meaning I have to
22:27provide a lot of energy for the
22:29hydrogen bond connections to break. Yes
22:33, it has cohesion and surface tension.
22:37Yes. Uh, cohesion speaks to the bonding
22:41capacity of the molecules, and surface
22:44tension to the force I have to exert to
22:46break the bonds the molecules form on
22:48the surface. You've seen that some
22:52insects can stay on top of the water or
22:54some leaves that stay on top of the
22:56water. Right? Why?
22:59Because of the tension.
23:00Because of the surface tension. Very
23:02good. Exactly, an attractive force is
23:06generated between the surface molecules
23:08that, for a solute or a compound to
23:10sink, it must break that force. So, the
23:17greater the attraction between water
23:19molecules, the harder it will be to
23:21break that bond. Right? Now, if I throw
23:26a nail, it will sink straight away. Yes
23:30. If I put a sheet of styrofoam, it
23:32won't sink. So, in addition to surface
23:37tension and weight, right, or the mass
23:39of the element, I also have to take the
23:41shape into account. Right? The greater
23:47the surface area the body in suspension
23:49occupies, right? Uh, the easier it will
23:52be for it to float. Yes, that is more
23:55or less what happens with boats. There
23:58is also another force. Yes. But well,
24:01let's not get into biophysics right now
24:03. Polarity, we continue talking about
24:09polarity, it is extremely important
24:11because it is what allows, for example,
24:14salt to dissolve. Yes, salt is sodium
24:21chloride, it's a crystalline lattice,
24:23it's formed by molecules of chlorine
24:26atoms and sodium atoms. Yes, they
24:31generate ionic bonds. Water, being a
24:36polar molecule, can dissolve because
24:41the chlorine, which has a negative
24:43charge, will be strongly attracted by
24:45this water molecule. Yes, the water
24:48molecule has no charge, but it is polar
24:50, as we said. So, the hydrogens
24:54represented here in gray, we said they
24:56are left with a positive charge density
24:58because the oxygen has a negative
25:00charge density. That means it tends to
25:04keep the electrons it shares with
25:06hydrogen in its orbit for longer. So,
25:11notice that around the chlorine we have
25:13a bunch of water molecules distributed
25:16with the hydrogens pointing toward the
25:18chlorine. Right? That is because the
25:23molecule is polar. Yes, because it has
25:25two poles, a negative pole and a
25:27positive pole. Water, as a
25:36characteristic, and before getting into
25:38acid-base equilibrium, water has the
25:41capacity to dissociate. Right? And when
25:47we talk about dissociation, in this
25:49case we are talking about the
25:51separation of the H2O molecule to form
25:53a hydronium ion, right? And a hydroxide
25:58ion. And now let's clarify one thing.
26:04The, uh, hydrogens, right? Their
26:08nucleus, how is it formed?
26:12By a proton. The nucleus of hydrogen is
26:15formed by
26:17a proton. Right? So, if that hydrogen
26:22loses the electron it has in its shell,
26:25right? What is left free?
26:31The proton. Right? So, when we talk
26:35about protons, right? About gaining a
26:38proton or losing a proton, we are not
26:40talking about just any element that can
26:42go around transferring protons. Protons
26:44are not transferred. Right? Now, when
26:48hydrogen loses the electron, right?
26:51Only the proton is left floating around
26:53. So, when we talk about protons at the
26:57pH level, we are talking about the
26:59dissociation of hydrogen. Right? Where
27:02all that remains of the hydrogen is the
27:03positive charge. Is this understood?
27:06Yes. All right, so colloquially you are
27:10going to see "proton," right? And
27:13hydroxide. Ideally, two water molecules
27:20join and form a hydronium, right?,which
27:23is H3 oxygen plus, right? And a
27:31hydroxide which is OH-which is the same
27:33as here. Yes. I repeat, colloquially we
27:39are going to talk about this. Ah, about
27:42the proton. We are going to make a
27:48definition that will also be useful for
27:50chemistry when you advance a bit more
27:51in the guides. Yes, but the definition
27:56we are going to make of acids or bases
27:58is related precisely to this proton, to
28:00the proton of the hydrogens. So, an
28:05acid is an ion or a compound that
28:08donates or yields or loses protons. Yes
28:13. Hydrogen plus. And a base is an ion,
28:19a compound, right? That can donate
28:24protons, that can accept protons. Right
28:27? So, when we talk about acids or we
28:30talk about bases, we are talking about
28:33the capacity to donate protons or
28:35accept protons. Yes, the capacity to
28:45donate or accept is also associated
28:47with, uh, solubility. Yes. When we have
28:57hydrochloric acid and we put it in
28:59water, it dissociates into protons and
29:06chloride anion. Yes. When we have
29:11potassium hydroxide, we put it in
29:13aqueous solution, it is also a salt
29:21a base accepts protons.
29:24Yes, it accepts protons. Now, we are
29:29generally going to see the base as OH-.
29:34Yes. Water, let's see, we said water
29:43can dissociate into protons and
29:45hydroxides. Right? So, if I add to my
29:50water solution the potassium hydroxide
29:53we were just looking at, meaning there
29:55are many free hydroxides left, right?
30:03it will act as a base or as an acid.
30:06Why?
30:10Because it will accept the hydrogens
30:12formed from the dissociation of water.
30:16Right? Let's go again. Water has a pH
30:22of 7, right? It is neutral. Why?
30:25Because the amount of protons and
30:27hydroxides is the same. Yes. An acid is
30:33that substance which can release
30:35protons and a base is that substance
30:37which can accept protons. So, the
30:41hydroxide can accept protons.
30:43Yes. Yes, it accepts one. So, the
30:46hydroxide is a base, right? So, when we
30:51have this, yes, in aqueous solution, we
30:56have the potassium
30:58and the hydroxide, how is it going to
31:00act?
31:01As a base. So, this is a base, is that
31:04understood?
31:06Yes. Good. This is a salt where we have
31:11a metallic compound, a non-metallic
31:13compound, right? Forming ionic bonds
31:17that can dissolve in an aqueous
31:19solution. Yes. pH scale, what is the
31:27range of the pH.
31:29From 0 to 14. And what does pH mean?
31:32What is pH?
31:33Potential of hydrogen.
31:34Potential of hydrogen. Yes. And what do
31:37we use it for?
31:41To know the acidity or basicity or
31:43alkalinity of a compound or a solution.
31:46Yes? So, when is a pH acidic?
31:54When it is lower than seven. Yes. From
31:56zero to seven. From zero to seven. Yes.
31:59And when is a pH basic?
32:01From 7 to 14.
32:03From 7 to 14. And when is it neutral?
32:05Seven.
32:06Seven. Yes. So, yes.
32:10Good. The pH scale goes from 0 to 14.
32:13Seven is neutral, seven is pure water,
32:15the water we were just looking at, yes?
32:17Where the amount of protons and
32:19hydroxides is the same. From seven
32:24downwards, the lower the scale, the
32:26lower the pH number, the more acidic
32:29the compound is. And conversely, the
32:34higher the pH, the more basic or
32:36alkaline the compound will be. Yes? Now
32:43, the pH formula is the one that
32:45appears here, which is the negative
32:47logarithm of the proton concentration.
32:53We are not going to break down the
32:55formula, but the more protons there are
32:57, the negative logarithm or the pH,
32:59what is it like?
33:02Acidic. Good. And how is it on the
33:04scale?
33:09From zero to seven. In other words, the
33:12higher the amount of protons, yes? The
33:16higher the amount of protons, the
33:18smaller the pH will be. So, a pH of 0.5
33:25is it more acidic or less acidic than a
33:28pH of 6?
33:30More acidic. Yes. Which one has more
33:33protons? The one at 0.5 or the one at 6
33:36?
33:36The 0.5 one. Yes. Why is pH useful to
33:47us and why are we talking about
33:48acid-base? Because in the body we have
33:55what are called buffer solutions or
33:57buffer systems. Yes? One of the
34:02examples of buffer solutions that we
34:04are seeing here, sorry, is the
34:06formation of carbonic acid. Yes. by
34:10means of the union of carbon dioxide
34:12and water. When is this carbonic acid
34:16formed? In what process? Do you know?
34:19Right? The students who are retaking
34:21the course know it is formed in
34:23cellular respiration. Yes? Why? What is
34:26released in cellular respiration?
34:29Carbon dioxide. Yes. Where to?
34:34It goes out to the environment
34:36afterwards. But in the body, where is
34:38it still? In circulation. Yes. And in
34:41circulation, the blood specifically,
34:44what is it made of?
34:46Water. So, we have carbon dioxide and
34:49water. Yes, it combines via an enzyme
34:54in the red blood cells. This part is
34:58called carbonic anhydrase, which allows
35:00for the formation of carbonic acid.
35:05This carbonic acid has the capacity,
35:07notice, a double arrow just like this
35:10one, to donate a proton, right? To lose
35:16a proton. So, what do we call that?
35:20Acid. Also, what did we call this
35:22compound? Carbonic acid. Right? So,
35:29carbonic acid is an acid that donates
35:32protons. Now, also this, which is
35:36bicarbonate, is a base. Why?
35:43Because it accepts a proton.
35:44Because it can accept this proton to
35:46lead to the formation of carbonic acid.
35:49Do you understand? So, this type of
35:55element is what we call a buffer or
35:57regulator, because it has the capacity
35:59to donate protons or lose them, donate
36:02protons or accept them, sorry. This
36:08acid, um, carbonic acid, right? Um,
36:17bicarbonate, sorry, has the capacity to
36:19yield another proton as well. Yes,
36:23it has another hydrogen here, so it can
36:25give up another proton. So, depending
36:30on what the pH of the medium is, it
36:32will accept or donate a proton. Right?
36:36And that is what makes it a regulator.
36:39The regulator is bicarbonate. Yes,
36:42because it donates a proton or accepts
36:45a proton. Is that understood?
36:47Yes. Bicarbonate is one example,
36:51phosphate is another that we will see a
36:53lot, and which is seen a lot in
36:55biological systems. Can you repeat what
36:59you said about the pH of the medium,
37:01yes? Depending on the pH of the medium,
37:06this bicarbonate can yield this proton,
37:09right? To regulate the pH, to make it
37:13more acidic. Or it can accept this
37:16proton, right? And to make it more
37:19basic, everything has an equilibrium.
37:24Yes, you will see later when you see
37:26diffusion, when you see chemical
37:28equilibrium, yes, you will see that
37:30everything tends toward equilibrium and
37:32to maintain a certain concentration. So
37:38there will always be a tendency to
37:40reach an optimal pH. Yes. Speaking of
37:50biomolecules, right? Which is one of
37:58the main things we are going to see,
38:00one of the main topics we will see in
38:02this unit. We are going to classify
38:06biomolecules into four groups:
38:11carbohydrates or sugars, right? lipids,
38:17proteins, and nucleic acids. These are
38:23the four types of macromolecules we are
38:25going to look at, right? And which
38:27actually form part of the cell. They
38:33are all organic compounds and are all
38:35joined by covalent bonds. Yes. To lead
38:38to the formation of each one of these
38:40macromolecules. We go back to the same
38:46thing. We had mentioned at the
38:49beginning that the basis for the
38:50structure and formation of
38:52macromolecules is the carbon atom. This
38:57carbon atom achieves these
38:58characteristics thanks to the nucleus
39:00it has and the four electrons found in
39:02the outermost layer. This allows it to
39:06have bonds with different types of
39:07elements. Now, silicon is in the same
39:15group, it also has four electrons in
39:17the outermost layer, however, it is not
39:20part of this central structure of
39:22biological compounds. Yes, we stick
39:27only with carbon. Carbon has the
39:34capacity to bond with four elements. We
39:40said, in the first case we have four
39:42identical elements forming a gas. This
39:45gas is methane. If a central carbon
39:48atom and four hydrogen atoms each
39:50fulfill the octet, then it is a stable
39:53molecule. They can form long linear
39:57chains. Yes, in the case above we are
39:59talking about a fatty acid. And this is
40:01what I was mentioning to you at the
40:03beginning. Take a look, that is a fatty
40:05acid chain. How many carbon atoms do
40:08you count? 1 2 3 4 5 6 7 8 9 10 11 12
40:1713 14 15 16. Yes. Notice that for every
40:25carbon atom, except for the first and
40:27the last, we have two hydrogen atoms,
40:29right? And that makes the proportion
40:34totally different. Branched chains can
40:39be formed, right? Bond, carbon, carbon,
40:42right? An element that is formed only
40:45by carbon and has this type of bond.
40:48The students who were just in chemistry
40:50with me, what type of element could
40:51that be? A diamond.
40:56Yes. Diamond is formed solely by carbon
40:59atoms, nothing to do with biological
41:02compounds. Yes, but diamond is formed
41:05solely by carbon atoms joined by
41:07covalent bonds. Yes. And graphite is
41:12also formed solely by carbon atoms, but
41:14there are carbon molecules. Yes. Carbon
41:18, carbon, carbon, with molecules, with
41:20other carbon molecules that join each
41:22other by means of another type of
41:24intermolecular force. Yes, that makes
41:27it much weaker. Beyond that, carbon's
41:31ability to form branched structures,
41:34right? Or to form cyclic structures,
41:38right? Through single or double bonds.
41:42Double bonds in this type of structure
41:44can undergo what is called resonance.
41:48which is a shift in the position of the
41:50double bonds. When we talk about a
41:52single bond, we are talking about a
41:57pair of electrons shared between one
41:59atom and another. And when we talk
42:02about double bonds, we are talking
42:04about two pairs of electrons shared
42:05between one atom and another. Right? So
42:11, the carbon skeleton is what allows it
42:16to give great diversity to
42:20macromolecules. The carbon skeleton
42:24alone is not enough. I mean, we said
42:28there had to be hydrogen and that, in
42:31turn, oxygen and nitrogen were also
42:33among the most abundant elements. To
42:39form the different types of
42:41macromolecules, we must also take into
42:43account other types of groups, right?
42:49And that is what we call functional
42:50groups. Functional groups in biological
42:54or organic chemistry are the ones here.
42:58Yes. Aldehyde, ketone, carboxylic acid,
43:03ester, amide, alkene, aromatic, primary
43:06amine, secondary, tertiary, alcohol,
43:10ether, and alkyne. Yes, these are the
43:15different functional groups that can be
43:17found in macromolecules. We are not
43:21going to see them all here in biology.
43:24You will see them in chemistry next
43:26semester. Yes. But we are going to
43:30focus, for example, on the hydroxide or
43:32hydroxyl group. R, keep in mind that R
43:39is a radical or a chain, and it is a
43:41carbon chain. R can be a CH3 or it can
43:46have many carbon chains. Yes, it is
43:50generic for any element of
43:56carbohydrates, or rather, of carbon
43:59chains, excuse me, that R. What
44:01interests us is the function, and the
44:03function is this here, an oxygen
44:10attached to a hydrogen, and this oxygen
44:12in turn attached to a carbon. Right?
44:18This compound or this functional unit
44:20is found in alcohols. Alcohol has this
44:25structure, it has that OH group. That
44:30OH group in alcohols makes it a polar
44:32molecule. Right? Why? Because oxygen is
44:39more electronegative than hydrogen. So,
44:44this oxygen will tend to have a
44:45negative charge density and the
44:47hydrogen a positive charge density.
44:51Right? With another alcohol. What type
44:54of bond will it be able to have then?
44:58Hydrogen bond.
44:59Hydrogen bond. Why? Potentially
45:05due to the difference in
45:06electronegativity.
45:07Due to the difference in
45:08electronegativity. And why? Because we
45:10have hydrogen and oxygen. Right? So,
45:16this creates very strong differences in
45:18electronegativity, which allows them to
45:21bond very strongly and stably through
45:23hydrogen bonding with another element
45:25that also has an OH group. Right? It
45:31could be another alcohol molecule or it
45:33could be water. So, if the elements
45:37have an OH group, will they be soluble
45:39or insoluble in water? Soluble.
45:42Soluble. What do we call it? Hydrox
45:46hydrophi
45:47hydrophilic. Yes, that’s correct.
45:49It’s a hydroxide. That’s fine.
45:51Hydroxide. If it separates. It’s a
45:53hydroxyl. Yes. It’s hydrophilic. It
45:55has an affinity for water. Yes. The
46:02sulfhydryl group. And this is provided
46:06by thiol groups, which is exactly the
46:08one marked here. It’s a sulfur with a
46:12hydrogen. This is extremely important
46:17when talking about proteins, because
46:19some amino acids, especially cysteine,
46:21have this group in one of their side
46:23chains, and that allows the tertiary
46:25structure of the protein—well,
46:27we’ll see it a little later—the
46:29tertiary structure of the protein to be
46:31stabilized in a very stable way, yes?
46:36Forming what are called disulfide
46:38bridges, yes? So, this functional group
46:43was not on the previous slide, but it
46:46is extremely important in biological
46:48systems. Another group is the carbonyl.
46:55And here in the carbonyl, we will find
46:59two different types of groups, what are
47:01called ketones and what are called
47:03aldehydes. The carbonyl is a carbon
47:09atom joined by a double bond to an
47:11oxygen. Saving this carbon. That is the
47:17carbonyl. Yes. You got a cramp.
47:24Someone help him out. So we have the
47:33carbonyl, which, depending on its
47:34location in a chain, we will call it a
47:37ketone or we will call it an aldehyde.
47:43If the carbonyl is bonded to a carbon
47:45atom on one side and another carbon
47:47atom on the other, we call it a ketone.
47:50Right? If it is bonded to a carbon atom
47:54on one side and a hydrogen on the other
47:56, we call it an aldehyde. This is
48:00important for sugars, because sugars
48:03can be ketones, yes? Ketogenic or
48:07aldehydes, yes? So, either aldoses,
48:10ketoses, or aldoses. There is a
48:14distinction regarding that with sugars
48:16that we are going to see now as well.
48:21The carboxyl is also extremely
48:22important for us because it is part of
48:25fatty acids. Yes, it is also partly
48:28part of amino acids. When we talk about
48:32amino acids, we are talking about an
48:34amino group and an acid group. This is
48:37the acidic group of amino acids. Right?
48:40Why? This carbon has a double bond with
48:45the oxygen, a single bond with this
48:47oxygen, and this oxygen has a single
48:49bond with the hydrogen. Depending on
48:54the pH, this hydrogen will be able to
48:56separate from this oxygen, right? And
49:01be left in this form, right? As an
49:04anion. So, upon losing this proton,
49:09what do we call this compound if it has
49:11the capacity to donate protons?
49:14Acid.
49:15Acid. So, this is a carboxylic acid.
49:21Right? Phosphates, the phosphate group,
49:32I don't think it was on the slide where
49:34you had all the functional groups
49:36either, but the phosphate group is
49:38extremely important in biology, because
49:44first, it is part of DNA, right? It is
49:48part of the phosphate group of
49:50nucleotides. Yes,
49:53it is part of ATP. What is ATP?
49:56Adenosine triphosphate. And how many
49:58phosphates does triphosphate have?
50:00Three.
50:00Three. And what is ATP used for?
50:05As an energy source. For what?
50:11For cellular respiration. Cellular
50:13respiration is the consequence, I mean,
50:15it is the cause or what generates ATP.
50:17What do we use ATP for? For the
50:22membrane. Right, it could be for the
50:28entry of molecules into the cell. For
50:30what? Muscular.
50:32Muscle contraction. Yes. Very good.
50:35Muscle contraction, if there is no ATP,
50:37it doesn't happen. Yes. What did you
50:39say here?
50:40For metabolism. Yes. What is metabolism
50:43?
50:46A set of chemical reactions. Good. To
50:49form or degrade compounds. Right? So,
50:53the formation of compounds implies
50:55energy expenditure, and that energy is
50:57provided by ATP. Yes, we have amino
51:03groups. The amino group forms amino
51:07acids. Right? Besides being part of
51:11amino acids, we will also find it in
51:13DNA. Yes, we will also find it, uh,
51:21well, in amino acids, but in the side
51:23chains as well. The importance of this
51:27amino group is that it is the opposite
51:30of a carboxylic acid. The carboxylic
51:32acid donates protons. Yes. The amino
51:35group can accept a proton. Right? So,
51:41how will it function in a biological
51:43system? As a base. Right? So, amino
51:49acids also function as a system in the
51:51body. Yes, it has an acidic group, the
51:57carboxylic acid, which can donate
51:59protons, and a basic group, the amino
52:01group, which can accept protons.
52:04Depending on the pH of the medium, the
52:06structures of each will be modified. Is
52:08it understood
52:10well? So, carbohydrates. I swear to you
52:19guys that I was putting the charts
52:21together last night for each of these,
52:23but I made them in, uh, Windows, and
52:25this is Linux, so the formatting got
52:27all messed up. It doesn't matter,
52:30it’s still visible and understandable
52:32. The important thing is that we're
52:34highlighting carbohydrates, meaning
52:36we're going to talk a little bit about,
52:38well, this went a bit further, yes,
52:40about carbohydrates. Carbohydrates are
52:43sugars. What do we use sugars for in
52:45the body?
52:47Mainly as an energy source. Nothing
52:49else?
52:50Structure.
52:50Structure. Very good. Where?
52:53The membrane.
52:54In the membrane. Forming part of what?
52:55Complexes.
52:56Gluco
52:57glycocalyx. Yes. Very good. Everything
53:00that says here. Glycocalyx. Yes.
53:02Glycolipids, glycoproteins. Very good.
53:05Also, where else will we find sugars?
53:08Where?
53:10In the matrix. Yes, forming the
53:13cellular matrix, taking part in, uh,
53:15energy reactions, where?
53:19In muscle tissue. Yes. For the same
53:22thing, to take part in, uh, obtaining
53:24energy.
53:25The oligosaccharides of the membrane.
53:28Yes, there we talk about glycolipids,
53:31uh, glycoproteins, right?
53:33Oligosaccharides. We are talking about
53:37the union of several sugars found in
53:39the outer membrane, in the external
53:40part of the cell membrane.
53:43Where else?
53:46What?
53:47In sperm cells. In the acrosome, yes.
53:50Also to obtain energy. Where else will
53:52we find sugar forming part of?
53:55In DNA molecules?
53:56In DNA molecules. Very good. Of DNA and
53:59RNA. Yes. The DNA and RNA molecules. We
54:03said so far they have a phosphate,
54:05right? And a sugar. What? And they will
54:10also have, uh, a nitrogenous group,
54:12which we will see later on, right? But
54:14they have an amino group there. So,
54:18primary energy source, structural
54:21function. What? Structural function,
54:26whether it's to give rise to the
54:28formation of DNA or RNA or the external
54:31structure of the cell. Sugars,
54:36monosaccharides, can be found in two
54:39states: in a linear state or in a
54:41cyclic state. Yes, goodbye. In the
54:48linear state, we find the carbon chain
54:50in a straight line, so to speak, with
54:52its components. Notice that here we
54:56already find different types of uh,
55:00functional groups. Yes. we find
55:03hydroxyls, right? And aldehydes. Now,
55:09in aqueous solution, this molecule is
55:12more stable with this configuration,
55:16which is a cyclic configuration. Yes?
55:21What is marked here in colors is the
55:23bond between carbon one and carbon five
55:25. Yes, by means of a peptide bond. Yes,
55:33to provide this cyclic structure. This
55:38is the example of glucose. The
55:42arrangement of hydroxyl groups in
55:43sugars is important because the
55:48different arrangement of the hydroxyls
55:50will make the molecule have a different
55:52name. Yes. Glucose, galactose. They
55:56will indeed change the name of the
55:57sugars according to the arrangement of
55:59the hydroxyls. We won't look at them
56:02now, but you will have to keep it in
56:04mind for other subjects. According to
56:09the number of carbons, we can classify
56:12sugars into trioses, right? Pentoses or
56:15hexoses, depending on whether they have
56:18three, five, or six carbon atoms. At
56:22the same time, we also said that we
56:24could classify sugars according to the
56:28type of, uh, functional group they had.
56:34They could be aldoses or they could be
56:36ketoses. According to the type and
56:41number of carbons, sugars have
56:43different names. Yes. Fructose, glucose
56:51you already know. Fructose surely
56:55sounds familiar, and we will highlight
56:57ribose, which has five carbons. Where
57:00does ribose sound familiar from? Where
57:02could it be?
57:03In.
57:04In RNA or in DNA. What is DNA? What
57:07does it stand for?
57:11Deoxyribonucleic acid. Right? So, that
57:17is the sugar that is part of DNA. Yes,
57:25you'll find them. Anyway, this class is
57:28going to be uploaded to the platform.
57:31Yes, we are recording. We are in HD, so
57:34it will be uploaded, you can watch it,
57:37repeat it, pause it, rewind it, fast
57:39forward it. Yes. Besides, we are also
57:45going to upload the presentation, the
57:47PowerPoint. The union of two
57:52monosaccharides forms a disaccharide.
57:56Yes, depending on the type of bond, we
57:58will classify it into different types
58:00of elements. Yes, we have disaccharides
58:05; if we keep adding glucose molecules
58:08or sugars, sorry, we will have
58:10polysaccharides. Poly means many, so
58:15saccharide refers to sugars. So it will
58:19be many sugars. Sugars have an
58:25orientation, a way of joining according
58:28to whether the chiral carbon bond goes
58:30up or down. It doesn't concern us now,
58:35but to explain, for example, this which
58:38is a beta 1-4 glycosidic bond and which
58:41we find especially in cellulose. Yes.
58:46Where do we find cellulose?
58:49In plants. Yes.
58:53Do you know what glycogen is?
58:56What is glycogen? It is an energy
58:58storage polysaccharide in animal cells.
59:00That is perfect. Yes. Again,
59:07it is an energy storage polysaccharide
59:09in animal cells.
59:10Yes, that was understood. It is an
59:13energy storage polysaccharide in animal
59:15cells. Yes. It is made up of a bunch of
59:19sugars. Yes? And the bond, notice that
59:23it is, well, alpha 1-4, alpha 1-6, it
59:26can bond to two, uh, through two
59:29different types of bonds, yes? A single
59:33glucose molecule can bond with two more
59:35glucose molecules. Let's move on. Yes.
59:45Lipids. Well, I hope it gets fixed
59:54later, but lipids are very diverse.
1:00:00While we generally tend to talk about
1:00:02lipids as non-polar substances, we are
1:00:08going to see some classifications of
1:00:10lipids where you will find, where we
1:00:12will see polarities. Yes. But generally
1:00:16, when we speak of water-soluble or
1:00:18fat-soluble, we are referring to
1:00:20whether an element is polar or
1:00:21non-polar. In general, lipids are
1:00:25non-polar. Yes. That is why it says a
1:00:31very diverse group, substances
1:00:32insoluble in water and soluble in
1:00:35non-polar solvents. Yes, they are
1:00:40energy sources. Yes. Fatty acids,
1:00:45triglycerides, the excess food that
1:00:47accumulates in us is stored as, uh,
1:00:50triglycerides. Yes. And this is an
1:00:54energy source. It has a structural
1:00:58function. We have phospholipids. And
1:01:00the phospholipids, where do we find
1:01:02them?
1:01:03In the plasma membrane. We also have
1:01:07glycolipids, which we can also find in
1:01:09the plasma membrane, and cholesterol,
1:01:11which we can also find in the plasma
1:01:13membrane. Yes. Lipids can act as
1:01:17biochemical messengers, since many
1:01:19lipids, or some lipids, sorry, are
1:01:22hormones, yes? Male or female sex
1:01:25hormones. Yes, they can also act as
1:01:31biochemical messengers, as second
1:01:33messengers. Yes, this is, a hormone
1:01:37arrives, it binds to a receptor, that
1:01:40generates a signal which is a second
1:01:42message to trigger a cascade of
1:01:44responses. Yes, you will see that later
1:01:48in biochemistry, and in fact, a course
1:01:50is given after you finish biochemistry,
1:01:52a course on biochemical messengers is
1:01:54given by the people from the
1:01:56biochemistry department as well. Yes,
1:01:59they have different functions such as
1:02:01forming part of lipoproteins. or, uh,
1:02:05forming vitamins. One of the main
1:02:14compounds we are going to see within
1:02:16lipids are fatty acids. Fatty acids,
1:02:19what function can you attribute to them
1:02:21?
1:02:26Right, energetic, yes? The carbon chain
1:02:32of the fatty acid is an energy source
1:02:34widely used by the body. It comes after
1:02:38the use of glucose. Yes? What else?
1:02:43Structure. Yes. Not the fatty acid
1:02:46itself, but it is part of the structure
1:02:48of phospholipids. Yes? Now, this fatty
1:02:54acid, right? Just as you see it, will
1:02:58it be a water-soluble or
1:02:59water-insoluble molecule?
1:03:03Why?
1:03:05Let's see, a molecule doesn't
1:03:08who says soluble and who says insoluble
1:03:10?
1:03:11Insoluble.
1:03:13The one that has one part or another
1:03:14part
1:03:15is very long.
1:03:16How long?
1:03:18It is very long. Good. Because the ends
1:03:25are polar and since the molecule is so
1:03:27long, the non-polar part is much larger
1:03:29than the polar part, so it has no
1:03:31tendency
1:03:36Right, the ends, only one, a single end
1:03:39is polar and the entire long carbon
1:03:41chain along with hydrogen is non-polar.
1:03:47So, in aqueous solution this part will
1:03:52be surrounded by water and all of this
1:03:54will not. So that will cause the fatty
1:04:00acids to not dissolve in water. Yes.
1:04:08Fatty acids will have a linear chain,
1:04:11right? They will have carbon atoms
1:04:16bonded to carbon atoms and hydrogen
1:04:18through single bonds, or they may have
1:04:20double bonds, yes? Carbon atoms with
1:04:26double bonds, which will cause a change
1:04:28in the structure, and this is extremely
1:04:30important when forming phospholipids.
1:04:35Yes, because this will allow the plasma
1:04:38membrane to have greater fluidity. When
1:04:46we talk about this type of fatty acid,
1:04:48we say that this fatty acid is
1:04:50saturated, meaning it has all single
1:04:52carbon-to-carbon bonds. Yes, they are
1:04:56single covalent bonds. Now, when we
1:05:00talk about this type of structure,
1:05:02right? Or this one here or this one, we
1:05:06are talking about unsaturated fatty
1:05:08acids. Yes? Which means there is at
1:05:12least one bond that is double with
1:05:13another carbon. Yes. This speaks to the
1:05:20famous saturated or unsaturated fatty
1:05:22acids. Yes. And the arrangement, we
1:05:27will see later if it is trans or cis as
1:05:29the year goes by. Triglycerides, an
1:05:39important source of lipid storage in
1:05:42the body, energy storage, not only
1:05:44energy storage, but also as structural
1:05:51or mechanical protection. Yes, because
1:05:55excess fat also prevents or acts as a
1:05:58protector. Yes, protection against
1:06:03impacts. So we have triglycerides
1:06:09referring to three fatty acids that are
1:06:11joined to an alcohol, which in this
1:06:13case is a glycerol molecule. Yes? And
1:06:20the glycerol joins with the fatty acid
1:06:22to form the triglyceride. Look, the
1:06:26glycerol atom joined with the
1:06:28carboxylic acid. This functional group
1:06:32we find here is called an ester group.
1:06:36Yes. And we have 1, two, three
1:06:40hydrocarbon chains. Yes. This is the
1:06:44typical triglyceride. Phospholipids are
1:06:51similar to triglycerides, but instead
1:06:53of having three fatty acid chains, they
1:06:56have two fatty acid chains and one of
1:06:58the positions is replaced by a
1:07:00phosphate group attached to a choline.
1:07:06Yes, regardless of what a choline is,
1:07:08right? We will see that in chemistry in
1:07:11the second semester. But we will have
1:07:15the glycerol, the phosphate, and the
1:07:16choline. Choline is characterized by
1:07:19having an amino group. If we said the
1:07:23amino group could act as a base by
1:07:25picking up protons, then this can give
1:07:27it a positive charge. If it has a
1:07:30charge, I can make it polar. So we have
1:07:34a phosphate group. The phosphate group
1:07:37is polar. Does a phosphate group give
1:07:42polarity to a molecule?
1:07:44Yes, a lot. Yes. So, we have glycerol,
1:07:51phosphate, and choline, which are part
1:07:53of the phospholipid head. Yes. The
1:07:58phospholipid head, what characteristics
1:08:00does it have? Is it soluble or
1:08:01insoluble in water?
1:08:03It is soluble. Yes, it is hydrophilic,
1:08:06and the tail, then, what are they like?
1:08:09Hydrophobic.
1:08:10Hydrophobic. So, phospholipids are
1:08:13molecules we call amphipathic. Right?
1:08:18Because on one hand they have an
1:08:19affinity for water and on the other
1:08:21hand they have a repulsion towards
1:08:23water.
1:08:26Hydrophobic.
1:08:27Hydrophobic, from phobos. Yes. It is
1:08:29afraid of water. What happens if we put
1:08:33many phospholipids? in aqueous solution
1:08:35.
1:08:39How
1:08:39does the membrane form?
1:08:41Well, a membranous structure is formed.
1:08:44Why is the lipid membrane a lipid
1:08:46bilayer?
1:08:49Because the fatty acid tails need to
1:08:51interact with each other.
1:08:53Why?
1:08:55So that the phosphate heads can
1:08:56interact with the water.
1:09:00Right. Yes. We said the heads here in
1:09:05these lollipops with two sticks refer
1:09:07to a phospholipid. The heads are polar,
1:09:11the tails are non-polar. The tails are
1:09:14afraid of water. So, when you put a
1:09:17bunch of phospholipids in aqueous
1:09:19solution, the heads like water, so they
1:09:20position themselves toward the outside
1:09:22to be in contact with the water, and
1:09:24the tails, since they are afraid of
1:09:26water, position themselves close to
1:09:28each other to avoid being in contact
1:09:29with the water. Yes, they are drawn
1:09:32together by the fear of water. So, the
1:09:36cell membrane has this lipid bilayer
1:09:38arrangement due to the properties that
1:09:40phospholipids have. Right? Notice that
1:09:48eventually this structure ends up
1:09:49forming, right? Which we find, uh, as a
1:09:53liposome uh, beyond the name. Yes, that
1:09:59is what ends up forming the cell. If we
1:10:02can add all the cell's organelles
1:10:04inside this liposome, it will be a cell
1:10:06. Right? So, in the cell, in the
1:10:12membrane, we are going to find
1:10:14phospholipids, glycolipids, cholesterol
1:10:16. Within the phospholipids, there are
1:10:20diverse types of phospholipids. Yes.
1:10:25Phosphatidylcholine, sphingomyelin,
1:10:27phosphatidylinositol, they have
1:10:28different distributions on one side or
1:10:30the other of the plasma membrane, but
1:10:32they are all phospholipids and that is
1:10:34what interests us for the moment. Yes.
1:10:43Sterols, another classification of
1:10:45lipids, are generally derived from
1:10:47cholesterol. What is the chemical name
1:10:50for cholesterol?
1:10:53Cyclopentanoperhydrophenanthrene. Yes.
1:10:59Cyclopentanoperhydrophenanthrene. That
1:11:01is the chemical name for cholesterol.
1:11:04Yes, for friends. Cholesterol. So this
1:11:11cholesterol forms or derives into sex
1:11:13hormones like testosterone, it can be
1:11:15part of bile salts, it has a structural
1:11:17function, because as we saw in the
1:11:19previous slide, cholesterol is part of
1:11:21the plasma membrane. Cholesterol in the
1:11:28membrane functions by modifying the
1:11:34fluidity of the membrane. Yes. We
1:11:44continue advancing through the
1:11:46macromolecules and we are going to
1:11:47focus now on proteins. Questions so far
1:11:53? Are we doing well? Yes. Is it hot?
1:11:58No.
1:12:00Yes. Could one of you over there tell
1:12:03Walter to turn on the air conditioning?
1:12:06Those in the back, Walter is the
1:12:08doorman. Please. Well. Proteins.
1:12:20Proteins, we also have a while to talk
1:12:22here because proteins have a ton of
1:12:24different functions. It was. Yes.
1:12:28Ah, it's on.
1:12:31Good. Great. Well, guys, the AC is on,
1:12:34so at this moment many would like to be
1:12:36out there, nice and cool, with air
1:12:38circulation. Proteins have a ton of
1:12:42distinct functions, structures, forms.
1:12:45Yes. The functions of proteins are very
1:12:48diverse. We have catalytic function and
1:12:52proteins we have enzymes, those are
1:12:58proteins that have a catalytic function
1:13:00, and catalytic function means lowering
1:13:02the activation energy for a reaction to
1:13:04occur. In other words, it increases the
1:13:09probability that a reaction occurs
1:13:11spontaneously. Enzymes, examples, there
1:13:15are a ton. "Lipase," what does it sound
1:13:17like to you? To lipids. Yes. And what
1:13:21will lipase do to lipids?
1:13:26Degrade the lipids. Yes. Very good. We
1:13:30have polymerases, we have isomerases,
1:13:33proteases, yes, there are a ton of
1:13:35enzymes, right? Or proteins that have a
1:13:40catalytic function and we call them
1:13:41enzymes. Yes. When we look at
1:13:44transcription, replication, and DNA
1:13:46duplication, you're going to get tired
1:13:48of hearing names of enzymes. They are
1:13:52regulators, right? They form hormonal
1:13:55structures such as, for example,
1:13:57insulin or glucagon. What is the
1:14:00function of insulin?
1:14:05To regulate blood sugar levels. How? By
1:14:08increasing or decreasing blood glucose?
1:14:10Decreasing.
1:14:11Decreasing. And glucagon, what does it
1:14:13do? Do you know?
1:14:14It increases it. Glucagon is the
1:14:17opposite in many ways to insulin. So,
1:14:20it acts during periods of fasting,
1:14:22increasing the amount of sugar in the
1:14:24blood. Yes. It acts as transport. Yes.
1:14:30An example is hemoglobin. What does
1:14:33hemoglobin transport? Let's see.
1:14:40Hemoglobin, where do we find it?
1:14:42In the blood.
1:14:43In the blood. In what part of the blood
1:14:45?
1:14:47In the red blood cells. And what does
1:14:49hemoglobin transport?
1:14:51Oxygen. So, it functions as transport.
1:14:53Yes. Another transport protein that is
1:14:57very abundant in blood is albumin. We
1:15:00were talking about lipids. We said that
1:15:03lipids were insoluble in water, that
1:15:05some lipids had hormonal functions,
1:15:08right? Or vitamin functions. Now, if
1:15:10they have to travel through circulation
1:15:12, they have a hard time because they
1:15:14don't dissolve in water; they don't
1:15:16like water. So, there are transport
1:15:19proteins, such as albumin, that are in
1:15:21charge of transporting these types of
1:15:23substances, hydrophobic substances,
1:15:27through the blood. Structural.
1:15:31Structural function. Proteins have a
1:15:33structural function. We are going to
1:15:36find, uh, proteins, collagen, the main
1:15:38structure that forms connective tissue.
1:15:42Yes. Uh, it is an extremely rigid
1:15:45structure. In insects and in nails or
1:15:51hair, we will also find a structural
1:15:53protein which is keratin. Yes, we will
1:15:59also have proteins that are in charge
1:16:01of movement. Yes, actin and myosin are
1:16:06the main proteins of, uh, muscle
1:16:08contraction, right? That is, the
1:16:11movement of the muscle and, in turn,
1:16:13also the movement of particles inside
1:16:16the cell. When we talk about proteins,
1:16:23we absolutely have to talk about amino
1:16:26acids. The amino acid is the structural
1:16:28and functional unit of a protein. A
1:16:31protein is formed by many amino acids.
1:16:34Right? And as we were just talking
1:16:37about, amino acids have an amino group
1:16:40and an acid group. So, the amino group
1:16:44is the NH group. Yes, in this case, it
1:16:50will be NH2. This amino group has the
1:16:53capacity to accept a proton. Yes. This
1:16:58is what would be an, uh, well, it is an
1:17:02amine. The carboxyl group, yes, is an
1:17:08acid, meaning it has the capacity to
1:17:10donate a proton. So we have the
1:17:16carboxylic acid and the amino group
1:17:18attached to a central carbon that we
1:17:20call the alpha carbon. This alpha
1:17:28carbon, in turn, has a single bond with
1:17:30hydrogen and another bond with an R
1:17:32group, which we said the R group was,
1:17:35uh, a radical, right? A representation
1:17:42that can be a carbon chain or not. Yes.
1:17:46Why do I tell you this? Usually they
1:17:48are carbon chains, but now we are going
1:17:50to see that there are some amino acids
1:17:52where this group is replaced directly
1:17:54by a hydrogen. All amino acids have
1:17:58this form, yes? This is the general and
1:18:01central structure of an amino acid.
1:18:05What will change among the different
1:18:06types of amino acids is the R group.
1:18:10And that R group will allow amino acids
1:18:12to have totally different functions and
1:18:14characteristics. Of course, depending
1:18:19on the type of R group they have, we
1:18:21are going to classify amino acids into
1:18:23different types, right? Or we will be
1:18:26able to include them in different amino
1:18:28acid families. We have non-polar amino
1:18:33acids with an aliphatic R group. Yes,
1:18:36aliphatic R group refers to a linear R
1:18:39group. Yes? Notice here we have
1:18:44hydrogen, CH3, CH3 CH3 CH3 CH3. Meaning
1:18:48there is no oxygen, there is no
1:18:50nitrogen. There is a sulfur here, but
1:18:57it’s not at the end of the chain, so
1:18:59it doesn't modify the behavior of this
1:19:01amino acid. So, all these amino acids
1:19:08here are non-polar. Yes, we have polar
1:19:15amino acids.
1:19:16Yes. that have a polar R group. Most of
1:19:22these have oxygen. Yes. Here is
1:19:25cysteine, which has a thiol group. Yes.
1:19:28Uh, here we have serine or threonine,
1:19:31which have alcohols. We also have some
1:19:34amino acids that have amino groups as
1:19:36side chains. Yes. We will also have
1:19:43polar amino acids with a charge. Yes,
1:19:47either positive charge or negative
1:19:49charge, depending on whether they are
1:19:51acids or bases. Yes, for example,
1:19:57lysine, arginine, and histidine have an
1:19:59amino group that can accept protons at
1:20:01the end of the chain, so that will make
1:20:04them basic, and if they are basic, they
1:20:06accept protons and in physiological
1:20:08solution if they accepted the proton,
1:20:10the charge they will have left will be
1:20:13positive. Yes? The opposite is
1:20:21aspartate or glutamate, or aspartic
1:20:23acid or glutamic acid, which have a
1:20:29carboxylic acid at the end of the side
1:20:31chain. In physiological solutions, that
1:20:35group will be deprotonated, so they
1:20:37will have negative charges. That is why
1:20:41they are associated with negatively
1:20:43charged R groups. Yes? And we also have
1:20:47prosthetic groups that are aromatic.
1:20:53Yes, these tend to be eh, variable in
1:20:55nature because here we have a hydroxyl
1:20:57group that gives it a certain polar
1:20:59character. And here we also have a
1:21:05structure, an imino group, that gives
1:21:07it, eh, a polar characteristic as well.
1:21:10Yes. But we classify them directly
1:21:13among the aromatics. Yes. No, among the
1:21:17polar or non-polar ones. Amino acids
1:21:23are joined together by means of what?
1:21:26Ionic bond.
1:21:27Peptide. Very good, it says so right
1:21:29there. And the peptide bond, what type
1:21:31of bond is it?
1:21:33Amide.
1:21:33Amide bond. Very good. Yes, it says so
1:21:36here. Amide bond. What type of bond
1:21:39does it present within the three types
1:21:41of bonds we mentioned? Ionic, metallic,
1:21:45or covalent bond?
1:21:47Covalent.
1:21:48Covalent. And all macromolecules are
1:21:51joined by means of covalent bonds. So,
1:21:56as you have already mentioned, two
1:21:58amino acids join together by means of a
1:22:01peptide bond, giving rise to the
1:22:03formation of an amide group, an amide
1:22:05linkage. An acid group joins with an
1:22:11amino group of another amino acid. Yes.
1:22:15The acid group of one amino acid joins
1:22:18with the amino group of another amino
1:22:20acid, giving a dipeptide. Yes,
1:22:25dipeptide refers to what will be the
1:22:27protein and also generating the release
1:22:29of water. We can keep adding peptides.
1:22:37Yes. or amino acids. And this peptide
1:22:41will increase; dipeptide, tripeptide,
1:22:43tetrapeptide, pentapeptide, up to nine
1:22:46we call it a peptide more or less, and
1:22:48then it would become a polypeptide or a
1:22:51protein. When we talk about proteins,
1:22:57we have to mention the different types
1:22:59of structures a protein can have.
1:23:01Excuse me, the formation of the two.
1:23:05Yes,
1:23:06is the union of two fatty [acids],
1:23:10right? Fatty acids,
1:23:12yes, two amino acids form a dipeptide.
1:23:16Yes. Three amino acids, tripeptide.
1:23:20Four amino acids, tetrapeptide. Yes.
1:23:23Several amino acids, oligopeptide. Many
1:23:26amino acids, polypeptide. Yes. And that
1:23:30can be a protein. The bond, the
1:23:34formation of this amide linkage, the
1:23:37joining of an acid group with an amino
1:23:39group of two different amino acids,
1:23:41generates the release of a water
1:23:43molecule. Good, so protein structures:
1:23:50primary, secondary, tertiary, and
1:23:53quaternary structure. Yes, all proteins
1:23:57have at least structure, they reach up
1:23:59to tertiary structure, and to have one,
1:24:01they must have the preceding ones. Yes.
1:24:07The primary structure refers to the
1:24:09sequence of amino acids, these amino
1:24:12acids we were just seeing that are
1:24:13joined together by means of this
1:24:15peptide bond. Yes, each of the amino
1:24:20acids has a particular name. So that
1:24:24sequence of amino acids with a first
1:24:26and last name is what we call a primary
1:24:28sequence. Yes. From how many amino
1:24:32acids is a protein formed?
1:24:35Uh, oligopeptides generally are not
1:24:41proteins. Yes. Polypeptides are. Uh, if
1:24:45I recall correctly, I think 40 to 50
1:24:47amino acids already allowed for the
1:24:49formation of a protein.
1:24:52Yes. So, the primary structure is the
1:24:55linear sequence of amino acids. The
1:24:59secondary structure is the interactions
1:25:01that this sequence of amino acids can
1:25:02have. Right? When we talk about
1:25:08secondary structure, we can talk about
1:25:13mainly two types of structure, which
1:25:15are alpha helix or beta pleated sheet.
1:25:19The alpha helix refers to the bond or
1:25:24the interaction, by means of hydrogen
1:25:26bonds, that stabilizes the structure,
1:25:28right?,of the amino acids of the same
1:25:30chain; while the beta pleated
1:25:36configuration refers to the bonding, by
1:25:42means of hydrogen bonds, of two chains
1:25:44that are adjacent. Right? This can be a
1:25:49sequence of amino acids going down and
1:25:51another sequence of amino acids going
1:25:53up. And this is just one sequence of
1:25:57amino acids that is bonded to itself.
1:26:01Now we will surely see some images and
1:26:02I hope it is understood a little better
1:26:04. The tertiary structure is the spatial
1:26:08configuration that this secondary
1:26:10structure can acquire. Yes, the sum and
1:26:14the arrangement of secondary structures
1:26:16, whether beta pleated or alpha helix,
1:26:18will form tertiary structure. Now, here
1:26:25there is a big difference regarding the
1:26:27types of bonds, because the secondary
1:26:29structure is stabilized solely by
1:26:30hydrogen bonds. These hydrogen bonds
1:26:35are formed between the amino groups and
1:26:40the acid groups. of the amino acid. Yes
1:26:45. That is, the generic amino acid with
1:26:49an amino group and an acid group
1:26:50attached to the central carbon, to the
1:26:52alpha carbon, will be what will
1:26:54generate the bond by hydrogen bridge
1:26:56with another amino acid to stabilize
1:26:58the secondary structure. The tertiary
1:27:04structure is stabilized by the bonds or
1:27:06the attractions that exist between the
1:27:08side chains. Yes, the R group will
1:27:13generate the tertiary structure. Yes,
1:27:23not all proteins have quaternary
1:27:24structure, some do, only those proteins
1:27:26that are formed by the union of at
1:27:28least two tertiary structures. If the
1:27:36main example of a protein with
1:27:38quaternary structure, what is it?
1:27:42Hemoglobin. Yes. So, take a look at a
1:27:49diagram a little nicer than the
1:27:50previous one, okay? We have the primary
1:27:54structure, right? With the amino acid
1:27:57sequence, the secondary structure as an
1:27:59alpha helix or as a beta sheet or beta
1:28:01pleated. There is a third type of
1:28:08structure which is by random
1:28:09arrangement or configuration, which
1:28:11would be this type of amino acids found
1:28:13here connecting two different
1:28:15structures, whether alpha helix or beta
1:28:17pleated. Yes, this is in case you see
1:28:24it in books, the random coil or random
1:28:27arrangement, but it is another type of,
1:28:29uh, secondary structure. We are mainly
1:28:32going to talk about alpha helix or beta
1:28:36pleated sheet. The tertiary structure
1:28:41is the arrangement in space of that
1:28:43secondary structure. Yes, the
1:28:46interactions between alpha and beta
1:28:49pleated sheet. And the union of two or
1:28:54more, in this case four, for example,
1:28:56of four of these tertiary structures,
1:28:59what we call subunits, four subunits
1:29:01will form the quaternary structure of
1:29:03hemoglobin. Yes, we have the same
1:29:10example again, secondary structure, the
1:29:13sequence of amino acids. Here, yes,
1:29:15secondary structure. Notice that this
1:29:19is amino acids. Yes, notice that here
1:29:24we have R, which means it can be any
1:29:26type of amino acid. And the hydrogen
1:29:32bond interactions are found between
1:29:34this amide group, yes? And this amide
1:29:40group here, yes? This generates the
1:29:43hydrogen bond interaction. Right? So,
1:29:48notice that here we are talking about
1:29:50the same sequence of amino acids, yes,
1:29:53which twist and are stabilized by the
1:29:55hydrogen bonds that the peptide bond
1:29:57itself forms. Yes? In the beta sheet,
1:30:05more or less the same thing happens.
1:30:08The side chains do not influence this
1:30:10distribution and this secondary
1:30:12structure. The peptide bond does
1:30:16influence it. Yes, the amide group. Now
1:30:21, this is one chain that goes that way
1:30:23and this is another chain that goes
1:30:25that way. Look at the green arrows. Yes
1:30:29. Now two chains. Yes, which continue
1:30:35to form the same protein, yes, are
1:30:37stabilized among themselves by means of
1:30:39hydrogen bonds. Yes, if we see it here,
1:30:44this could be a beta pleated sheet. If
1:30:48we analyze it this way, that alanine
1:30:50and glycine bind to each other by means
1:30:52of a hydrogen bond. Yes. And each one
1:30:56of these amino acids binds to each
1:30:57other by a hydrogen bond. Yes. and it
1:31:00stabilizes the tertiary structure. Here
1:31:09we have hydrogen bonds too, but it is
1:31:11not the only or the main type of
1:31:13interaction that can occur between, uh,
1:31:15amino acids. Here the side chains are
1:31:20indeed involved. Notice that we can
1:31:24have an ionic bond between a basic
1:31:26amino acid and an acidic amino acid.
1:31:30Yes, we can have a disulfide bridge
1:31:32from an amino acid, from the union of
1:31:35two amino acids that have, uh, thiol
1:31:37groups. This disulfide group is found a
1:31:42lot in the structure of hair. Yes. When
1:31:46you straighten your hair, what you are
1:31:48mainly doing is breaking this sulfur
1:31:50bridge. Yes, the hydrogen bond, notice
1:31:58that it also occurs between amino acids
1:32:00that are polar. Yes, we also have
1:32:04attraction through van der Waals forces
1:32:06. We can also see it as an attraction
1:32:10by repulsion, right? Due to
1:32:12hydrophobicity. Notice that these tails
1:32:15are hydrophobic, yes? So, out of fear
1:32:20of water, they join and attract each
1:32:22other, giving rise to the tertiary
1:32:24structure of proteins. Yes, more or
1:32:28less something like this in a
1:32:30three-dimensional image. Yes, we can
1:32:33also classify proteins. That looks so
1:32:36ugly. Into fibrous or globular. Yes, it
1:32:41has nothing to do with secondary or
1:32:43tertiary structure, rather it has to do
1:32:45with the three-dimensional structure,
1:32:47the tertiary structure that proteins
1:32:50form. Right? A classic example of a
1:32:53fibrous protein is collagen. Yes. And a
1:32:58globular protein can be any enzyme. Yes
1:33:01. And notice here, it is showing you as
1:33:04an example a cavity of an active site,
1:33:06yes? Characteristic of enzymes, right
1:33:11where the chemical reactions catalyzed
1:33:13by this enzyme will occur. The terms
1:33:19fibrous and globular refer to their
1:33:21shape. Yes, this one has a fiber
1:33:24structure and this one has a more
1:33:26rounded globular structure. Yes, if you
1:33:29look closely, it looks like a cloud, a
1:33:32cumulus cloud. Yes, those beautiful,
1:33:35fluffy clouds that form nicely. One
1:33:39last thing and we finish. Come on, we
1:33:48have until 1:30. We can continue if you
1:33:50want. Uh,
1:33:55nucleic acids. Yes, when we talk about
1:34:01nucleic acids, we are talking about DNA
1:34:04and RNA. DNA, deoxyribonucleic acid,
1:34:10RNA, ribonucleic acid. The structure of
1:34:16fatty acids, sorry, of nucleic acids,
1:34:18yes? Is given by a phosphate group, a
1:34:23sugar, yes? a pentose, specifically a
1:34:27ribose, and a nitrogenous base. The
1:34:34importance that nucleic acids have is
1:34:36none other than containing the genetic
1:34:38information of the cell. It is
1:34:43everything that is transmitted from
1:34:44parents to children, from mother cells
1:34:46to daughter cells through cell division
1:34:48. Yes, it is heredity, it is everything
1:34:52that will define protein structure.
1:34:54Broadly speaking, right? At the genetic
1:34:57level, the structure of proteins, the
1:35:00sequence of amino acids, uh the shape
1:35:02of cells, the structure of cells,
1:35:04everything is stored in memory, yes?
1:35:11Everything is stored in DNA and in its
1:35:13child, RNA. If you look for something
1:35:19very funny, if you search on Google for
1:35:22"DNA creed," yes, you will see a whole
1:35:24...uh well, a prayer, yes, regarding
1:35:35DNA by some fanatical biologists or
1:35:37geneticists. Yes, I believe, I believe
1:35:41in DNA and in its son, its only son,
1:35:44RNA, which was formed in the nucleus.
1:35:46Yes, very funny. Look it up later and
1:35:49laugh by yourselves at home, like I did
1:35:51on Saturday night. The structure of a
1:35:57nucleic acid is this. Yes, a sugar. Yes
1:36:06, we'll repeat it again, it's a ribose
1:36:08or a deoxyribose depending on whether
1:36:11it's DNA or RNA. It's a deoxyribose
1:36:17depending on whether this position that
1:36:23says two prime, each of these points
1:36:25refers to a carbon. Yes. If there is a
1:36:31hydroxyl group on this carbon, it's a
1:36:33ribose. If there is no hydroxyl, an OH
1:36:37group, it is deoxy because it lacks the
1:36:40hydroxyl. Yes, deoxyribose. Yes. This
1:36:49that says here, acid group, is why it
1:36:52is called amino acid, uh, sorry,
1:36:54nucleic acid. I am really struggling
1:36:59with "nucleic acid". I already called
1:37:01it fatty acid and then I said, uh,
1:37:03amino acid. The nucleic acid is an acid
1:37:07because it has this group here, which
1:37:09is a phosphate group. The phosphate
1:37:13group has in its arrangement a
1:37:15phosphate and four oxygens as a
1:37:17phosphate group itself. When it is
1:37:20attached here to this carbon, which is
1:37:25called carbon five within the sugar,
1:37:27right? Three phosp—three oxygens
1:37:31remain. Yes. And of those oxygens,
1:37:34there are at least two that have the
1:37:36ability to bind to protons. Therefore,
1:37:40in solution, they can donate protons or
1:37:43accept protons depending on the pH of
1:37:45the medium. Yes, that's why it is an
1:37:48acid. This phosphate group is what we
1:37:55will call or will find as monophosphate
1:37:57, diphosphate, and triphosphate. This
1:38:04phosphate group and the position are
1:38:05extremely important because this
1:38:07position is the five prime. Right? And
1:38:13for those who already have some idea,
1:38:15why is the five prime position of a
1:38:17nucleic acid important, and the three
1:38:19prime position,
1:38:25right? For
1:38:29DNA transcription. Yes. Transcription
1:38:33or replication, how the different
1:38:35nucleic acids join together. Not
1:38:40everything, not the mechanism, but the
1:38:42nucleic acids join one to another
1:38:47through a five prime and three prime
1:38:49end. Right? The three prime end of this
1:38:55nucleic acid will join with the five
1:38:57prime end of another nucleic acid and
1:38:59that will form DNA or RNA. Right? The
1:39:09third component of this nucleic acid is
1:39:11the nitrogenous base. The nitrogenous
1:39:15bases, what are they?
1:39:19Adenine, guanine. Cytosine, thymine
1:39:23and uracil.
1:39:25Yes, for DNA and for RNA it is the same
1:39:30.
1:39:30No,
1:39:31no. Why?
1:39:35Because for RNA we have uracil. And
1:39:37which one don't we have?
1:39:39Thymine. And we have, uh, uracil in DNA
1:39:42,
1:39:43right?
1:39:43No. What do we have?
1:39:45Thymine.
1:39:46Thymine. So, the DNA bases will be
1:39:49adenine, guanine, thymine, and cytosine
1:39:52. And the RNA bases will be adenine,
1:39:55guanine, cytosine, and...These
1:40:01nitrogenous bases can be classified
1:40:04into purines or pyrimidines. Why?
1:40:08Because they have different structures.
1:40:10Adenine and guanine are two aromatic
1:40:12rings. Uh, they are two rings, sorry.
1:40:15And thymine and cytosine are just one.
1:40:18Now we are going to look at some images
1:40:19and I hope it stays a bit
1:40:20the name of purines and pyrimidines.
1:40:23Yes, it's the same thing. Yes, purines
1:40:25or pyrimidines. Yes. Now, I remembered
1:40:29it this way. Adenine and guanine are
1:40:32purines. So, pure water, yes. Adenine,
1:40:40guanine, water. Yes. Pure for purine.
1:40:45So, water is pure. Adenine, guanine,
1:40:49purine. Yes, I know it's a bit
1:40:52far-fetched. Well, it worked for me
1:40:55that way. Water a So, adenine, guanine,
1:41:04purine. Yes. And cytosine and thymine,
1:41:08by elimination, have to be pyrimidines.
1:41:11Yes. Good. We have a distinction. Yes.
1:41:17Watch the replay at home later and try
1:41:19to follow along. We are going to make a
1:41:24distinction because they are two
1:41:26different things, what a nucleoside is
1:41:28versus what a nucleotide is. Right? The
1:41:33nucleoside refers to the sugar and the
1:41:35nitrogenous base. Right? And we call it
1:41:40, for example, adenosine. Now, the
1:41:46nucleotide has the phosphate group.
1:41:50Right? So, this will be adenosine,
1:41:55triphosphate, monophosphate, or
1:41:57diphosphate, depending on the number of
1:41:59phosphates it has. So then, the
1:42:03nucleoside is without phosphate and the
1:42:05nucleotide is with phosphate; they are
1:42:07two different things. Right? So, again,
1:42:17the pure bases, for me, the purines are
1:42:20adenine and guanine. This is what I was
1:42:25mentioning to you, that they are two
1:42:27rings that are joined. Yes. And the
1:42:32pyrimidines are all, um, a single ring,
1:42:38right? A cyclic structure, yes. Unique.
1:42:46There are differences between them, as
1:42:48well. Let's stop here for a moment.
1:42:52Look, thymine and uracil each have a
1:42:55carbonyl group. an amino group, a
1:43:00carbonyl group here, an amino group
1:43:03here, a CH, a carbon with a CH3, and
1:43:10here a carbon with a hydrogen. The
1:43:14difference then between thymine and
1:43:20uracil is in this methyl group that is
1:43:22right here. Yes. And you can't see it
1:43:28well here, but here there is, uh, a
1:43:30double bond. Yes, but that is the
1:43:35difference between DNA and RNA. Yes.
1:43:40It's not a very big difference when
1:43:42talking about one element or the other,
1:43:44right? Yes. Thymine and uracil are two
1:43:46different things because one is in DNA
1:43:49and the other in RNA. We are only
1:43:52talking about a CH3, right? And a W.
1:43:58Watson and Crick, absolute legends, yes
1:44:01, discoverers of the DNA double helix.
1:44:04I don't know how they did it from
1:44:06X-rays. They saw an X there and said it
1:44:09was a double helix. Yes, I still don't
1:44:12understand it, but it doesn't matter.
1:44:14They discovered it. It was proven to be
1:44:17that way. DNA has a double helix. Helix
1:44:23, in fact, because it rotates, as shown
1:44:26in the figure, and it is double because
1:44:28there is a union between bases. Right?
1:44:32Which bases pair with which? The base
1:44:36is the nitrogenous base. Right? So,
1:44:41adenine with thymine
1:44:42and cytosine with
1:44:44and cytosine with guanine. Yes. In
1:44:46college many years ago, they told me
1:44:49Carlos Gardel and Aníbal Troilo. Yes,
1:44:54so you remember just in case. And
1:44:59Carlos with Cytosine with Guanine and
1:45:01Thymine with Adenine. Yes. Well, that
1:45:09was a long time ago, guys. You can find
1:45:12another like Watson and Crick try to
1:45:17find another example. Watson and Crick
1:45:21double DNA. Yes, the unions are
1:45:25produced by hydrogen bonds between the
1:45:31groups, uh, between, uh, the side
1:45:34chains, between uh the nitrogenous
1:45:41groups. Right? So, guanine joins with
1:45:44cytosine. Notice that guanine has three
1:45:49places to form hydrogen bonds and so
1:45:51does cytosine. So, the two DNA strands
1:45:57join together through this triple
1:45:59hydrogen bond union between guanine and
1:46:02cytosine. That is why guanine and
1:46:06cytosine join together. Adenine and
1:46:11thymine join together through two
1:46:13hydrogen bonds. Yes, that's why that
1:46:18interaction occurs between them. Yes.
1:46:22No, because they have a different shape
1:46:26, as is usually graphed here. Well,
1:46:28this has a tip, a space to include, to
1:46:31put this tip, and this one a circle
1:46:33here. So they join and that's it, right
1:46:37? Because they fit in shape, it's
1:46:39because of the number of hydrogen bonds
1:46:41that can be formed. So uracil in RNA
1:46:45joins to adenine, that is, instead of
1:46:48thymine we have uracil and cytosine
1:46:50joins with guanine. Watch out here
1:46:54because RNA is not a double strand. RNA
1:46:59is a single strand, right, which has
1:47:02roughly the same structure as DNA,
1:47:04right? And instead of thymine, it has
1:47:09uracil. And for RNA to be stable in
1:47:13solution, it acquires a secondary
1:47:16structure, a, uh, three-dimensional
1:47:18configuration that stabilizes it. Since
1:47:22it does not have a double helix, a
1:47:27sequence, uh, to pair with, it is
1:47:30stabilized by a random arrangement. DNA
1:47:35is a double, a, uh, double strand,
1:47:39right? Helical, always more or less
1:47:43coiled. Now, the RNA, the secondary
1:47:47structure it has is random, right? It
1:47:51varies between different RNAs. It will
1:47:57vary according to the arrangement of,
1:47:59uh, the sequence; it will vary
1:48:01according to the length of the sequence
1:48:03. Yes, there will be many variables. So
1:48:08, the difference between DNA and RNA.
1:48:12Yes, we have ribonucleic RNA, DNA, deox
1:48:16-on the carbon two, deoxyribonucleic.
1:48:21Yes, they all have a phosphate group.
1:48:24Look at this, what I was telling you
1:48:26here, they have a negatively charged
1:48:28oxygen, another negatively charged
1:48:30oxygen. This has the capacity to bind a
1:48:33proton, so that is why it is an acid.
1:48:36Yes. Although in physiological solution
1:48:39, in aqueous solution, in the cell, we
1:48:42will always find it deprotonated. The
1:48:46bases can be, for DNA, thymine, adenine
1:48:49, cytosine, and guanine, and for RNA,
1:48:52uracil, adenine, cytosine, and guanine.
1:48:57Yes, we have the double-strand
1:49:00interaction for DNA, and in RNA, a
1:49:02single chain. Yes. Again, as a final
1:49:08image, what a nucleic acid is. Here it
1:49:13is explained in another way, for
1:49:16example, adenine with, uh, its three
1:49:18sites where it can have bridge, uh,
1:49:20sorry, its two sites where it can have
1:49:22hydrogen bond junctions. It is a
1:49:27structure with two rings. Yes. The
1:49:32ribose, right? With its hydroxyl on the
1:49:35carbon two. Yes. And, uh, we have here
1:49:40the three phosphate bonds of the
1:49:42triphosphate. Right, that's it, we're
1:49:51done, guys. Uh, remember that you can
1:49:56watch the video as many times as you
1:49:58want on the platform. Yes. And we have
1:50:04this class, the practical work, next
1:50:07week. To the students outside, please,
1:50:10I'm going to ask you to wait to enter
1:50:12until those in here leave, otherwise
1:50:14it's going to be a mess.
1:50:22Yes, I'm coming. Wait while I see about
1:50:25turning this off.

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