YT YouTube2Text

YouTube2Text → Transcripts → Digestión de proteínas, absorción y transporte de aminoácidos

Digestión de proteínas, absorción y transporte de aminoácidos — Transcript

by Metabolismo · 2,812 words · 447 segments · language en · Watch on YouTube

Open in transcriber Summarize with AI Download SRT/VTT

Full transcript

0:03In this opportunity, we are going to
0:05talk about protein digestion. We have
0:09proteins in various foods, foods of
0:11animal origin and foods of plant origin
0:13. Foods of animal origin have
0:17high-quality proteins; that is, their
0:19proteins have the amino acids the human
0:22body needs, and the amount of those
0:24amino acids the body needs is also
0:26greater. But let's focus on the fact
0:30that we utilize proteins from food,
0:33whether of animal or plant origin. The
0:37proteins in these foods have a
0:39three-dimensional structure; the vast
0:41majority of them are in tertiary or
0:44quaternary structures, and with that
0:46structure, they can have various
0:48functions. They can be enzymes, they
0:51can be receptors, they can be
0:52transporters. When we cook food, for
0:57example, we denature those proteins,
1:00and polypeptides, or linear structures
1:03of amino acids, can be generated. Each
1:08one of these components is an amino
1:10acid. Amino acids that are joined by a
1:14peptide bond. The bond that joins these
1:17two amino acids is a peptide bond. This
1:19one with this one, the junction here is
1:21a peptide bond. And we have a
1:23polypeptide that has an amino-terminal
1:25or N-terminal end and a
1:27carboxyl-terminal or C-terminal end. By
1:30convention, the amino group is on the
1:32left side, the amino group of a
1:35polypeptide, and the carboxyl group is
1:38at the right end. What is the objective
1:42of protein digestion? That we degrade a
1:47polypeptide, break the peptide bonds to
1:50release amino acids. We break this
1:53peptide bond, for example, we release
1:54an amino acid. We break this peptide
1:57bond, we release an amino acid. And so,
2:00digestion will promote the release of
2:02free amino acids that the human body
2:04will utilize. Each of our cells will
2:08use those amino acids to form new
2:11proteins. So, in the diet, we can
2:14acquire proteins in a native state or
2:16in the form of a polypeptide. That will
2:19depend on whether or not we have cooked
2:21the food. That is why cooking is called
2:23a pre-digestion, because what it does
2:25is that the temperature denatures the
2:27proteins. So, in the mouth, there is no
2:32protein digestion; that is, we will not
2:34be able to break peptide bonds, that
2:36will not be possible. What happens in
2:39the mouth is mastication. Mastication
2:41is very important because what it does
2:43is break the cells of these foods and
2:46release the protein content. So, in the
2:50mouth, there is no digestion; what
2:52occurs is the release of the proteins.
2:56Now, that content will pass through the
2:58esophagus and arrive at the stomach. In
3:01the stomach, there are two very
3:05important cells, which are the parietal
3:07cells and the chief cells. The parietal
3:11cells release hydrochloric acid, the
3:13parietal cell or oxyntic cell. That
3:16hydrochloric acid will stimulate or
3:19promote the pepsinogen that was
3:21released by the chief cell to convert
3:23into pepsin. This chief cell released
3:27pepsinogen and the parietal cell,
3:30hydrochloric acid. Pepsinogen is
3:33activated in the presence of
3:34hydrochloric acid and turns into pepsin
3:36. That pepsin is an enzyme that breaks
3:40peptide bonds. We could call it a
3:43protease or peptidase. It is a
3:46proteolytic enzyme because it breaks
3:48peptide bonds. When pepsin is formed,
3:51it can itself promote more pepsinogen
3:53to turn into pepsin. Two very important
3:57things. First, hydrochloric acid will
4:00promote a high concentration of protons
4:03in the stomach, meaning acidity
4:05increases, and when acidity increases,
4:08the pH value drops. That is why there
4:12is a pH between 1 and 2.5 in the
4:14stomach. It is very important not to
4:19over-consume water, because if we drink
4:23too much water, the acid will be
4:26diluted and the pH will rise. It is
4:31very important that we maintain this pH
4:34value in order to denature proteins. If
4:38we drink too much water, we will cause
4:40that pH to fall out of this range and
4:42we will not be able to denature the
4:44proteins we are consuming. Mainly when,
4:47for example, someone does not chew well
4:49. If someone does not chew well, all
4:53the content will pass through and those
4:55proteins will not be properly released
4:58or properly denatured, which will
5:00prevent us from digesting the proteins.
5:05Now, what is the other important point
5:06I wanted to mention to you? Pepsin is a
5:08proteolytic enzyme because it breaks
5:11peptide bonds. We said that the acid
5:15promoted the protein in its native or
5:17three-dimensional state to denature and
5:20form a polypeptide like this one.
5:24Pepsin breaks peptide bonds, but not
5:27just anywhere. It breaks peptide bonds
5:30that are in the center of the
5:32polypeptide. For example, it can break
5:34here, it can break here, here, here. We
5:38could call pepsin an endopeptidase
5:40because it likes to break peptide bonds
5:42in the center of the polypeptide. Let's
5:45assume that the pepsin will break this
5:47peptide bond. It breaks this peptide
5:51bond because remember it is an
5:53endopeptidase; it likes to break
5:54peptide bonds in the center of the
5:56protein. A fragment like these will be
6:00generated, right? Do you see? The
6:04polypeptides, which can come from large
6:07proteins, are being fragmented thanks
6:10to pepsin in the stomach. Now, this
6:14free carboxyl end would be this one,
6:17and now what is exposed here would be
6:20the amino group, and there we have it:
6:22a large polypeptide has been fragmented
6:25, and this happens with many proteins
6:28in the diet thanks to pepsin. Now, all
6:32the stomach contents will pass into the
6:35small intestine. In the small intestine
6:40, there are cells. These cells are
6:43enterocytes. This cell is an S cell.
6:47This is an I cell. This I cell and S
6:51cell are enteroendocrine cells. These
6:56enterocytes are epithelial cells. Now,
7:00what happens? The acidic stomach
7:03contents arrive, containing the
7:06components we consumed, and that acid
7:09stimulates the S cell, this cell here.
7:14It stimulates that S cell to release
7:16secretin. The acidic content arrives
7:20and stimulates the S cell, secretin is
7:22released, and that secretin travels
7:24through the blood, telling the pancreas
7:26to release bicarbonate. Bicarbonate
7:32alkalizes or neutralizes the acid
7:35coming from the stomach, reaching a pH
7:39of 7 to 8 in the small intestine. Also,
7:46the pepsin that arrived from the
7:48stomach won't be able to work because
7:51it likes an acidic pH, and since it is
7:53now in an alkaline pH, it is
7:55deactivated. And who will continue the
7:59work that pepsin did? Let's look at
8:02this first. The content from the
8:06stomach will also stimulate other cells
8:09, which are the I cells. These I cells.
8:13This I cell releases CCK, also known as
8:17cholecystokinin or pancreozymin. CCK
8:22promotes the gallbladder to release its
8:25contents and the pancreas to release
8:27its proteolytic enzymes. Bile is not as
8:32important in the context of proteins.
8:35Let's focus on the pancreas. The
8:36pancreas releases its enzymes, but not
8:39in active form, rather as zymogens. Who
8:42are these zymogens that the pancreas
8:44releases into the intestine? Let's see.
8:48The pancreas releases these zymogens:
8:51trypsinogen, procarboxypeptidase A,
8:53procarboxypeptidase B, chymotrypsinogen
8:56, and proelastase. Why are they called
8:59zymogens? Because they are enzymes in
9:02an inactive form. And how are they
9:06activated? Who starts the activation
9:08process? Let's see. First, we said the
9:11pancreas released its content into the
9:13small intestine. In the small intestine
9:16, there are enterocytes. These
9:19enterocytes may have an enzyme on their
9:21apical membrane called enteropeptidase.
9:25That enteropeptidase can activate
9:28trypsinogen to become trypsin. This
9:31trypsin is a proteolytic enzyme, it
9:34breaks peptide bonds and will help in
9:37protein digestion. This trypsin, which
9:40is in its active form, will promote
9:42more trypsinogen to turn into trypsin.
9:46It doesn't end there. That trypsin is
9:49now active and will activate the rest
9:52of its counterparts, the zymogens. It
9:56will activate them so they convert into
9:58their active forms. All these enzymes
10:01are proteolytic enzymes. They like to
10:05break peptide bonds, but they don't
10:07break them just anywhere; they have a
10:10certain specificity. And let's see how
10:14that happens. Look, here we have pepsin
10:18, chymotrypsin, trypsin, and elastase.
10:21These enzymes are considered
10:23endopeptidases because they like to
10:25break internal peptide bonds. That is
10:30to say, they like to break peptide
10:31bonds that are in the middle of the
10:33polypeptide. Do you remember what
10:37pepsin did? Very good. These three like
10:41to do the same thing; they like to
10:43break peptide bonds in the center. For
10:45example, trypsin is an endopeptidase.
10:49Let's assume it’s going to break a
10:51peptide bond in the center and we’ll
10:53get something like this. See? It has
10:57broken this peptide bond that joined
10:59these two amino acids. Chymotrypsin
11:03comes along and, as we said, it likes
11:06to break a peptide bond in the center.
11:09Here we have a smaller polypeptide that
11:11has been formed. There are two here
11:13that have been formed. Now, trypsin or
11:16chymotrypsin can act here and break in
11:20the middle. Another endopeptidase comes
11:24along and breaks in the middle. Do you
11:28see? And so we have endopeptidases
11:30gradually generating smaller fragments.
11:35What about the carboxypeptidases that
11:37were also released by the pancreas in
11:40an inactive form and then activated in
11:43the intestine? These carboxypeptidases
11:47like to remove or break peptide bonds
11:50on the C-terminal side, that is, those
11:53closest to the carboxyl group. And
11:57let's look at the scenario. We have a
12:00carboxypeptidase A or B. Do they like
12:02to break peptide bonds that are close
12:05to the carboxyl group? We can have this
12:08scenario. A carboxypeptidase comes
12:10along, breaks here, and an amino acid
12:12is released. Another carboxypeptidase
12:15breaks here, and this dipeptide is
12:17released. Another one comes along here.
12:20There it is. And so we have
12:23carboxypeptidases that like to cut at
12:25the C-terminal or carboxy-terminal end.
12:28And now the aminopeptidases; we hadn't
12:31said anything about them until now.
12:34These aminopeptidases are found on the
12:38brush border. They are there on the
12:42brush border of the enterocytes. The
12:44aminopeptidases are there. What do the
12:47aminopeptidases do? They break peptide
12:51bonds that are close to the amino group
12:54. And here we can have an
12:57aminopeptidase break here, another
12:59aminopeptidase break here, and another
13:01aminopeptidase break over here. And so
13:04we have proteins being broken down from
13:07this end thanks to the aminopeptidases.
13:12And so we have this scenario. You can
13:16take a picture of this. There is much
13:19more biochemistry involved because
13:23these enzymes break amino acids at
13:26specific places and have a certain
13:30preference for specific amino acids.
13:34That's why I've listed some here where
13:36they like to break. But let's keep in
13:40mind this general classification:
13:42endopeptidases, aminopeptidases, and
13:44carboxypeptidases. There are various
13:46aminopeptidases, by the way; I've
13:48explained where they like to function
13:50simply for the sake of clarity. Now
13:53let's continue and understand a bit
13:55more about the process. These proteins
14:00were processed in some way by pepsin;
14:03pepsin already did some work. Now these
14:07proteins move on to the small intestine
14:09. They had already arrived there,
14:10remember. And now in the small
14:12intestine, we are going to zoom in on
14:15this area of enterocytes. Here we are
14:18going to locate ourselves in the small
14:20intestine. Here we have enterocytes.
14:23Enterocytes. There are several brush
14:26border enzymes there. There is the
14:29aminopeptidase, we have the dipeptidase
14:30and tripeptidase, which we will comment
14:32on in a moment regarding what these two
14:34do. There are transporters that will
14:37take advantage of the amino acids. And
14:39let's see how the digestion of proteins
14:42is finished. We are going to increase
14:45the size a bit to visualize it better.
14:48We have several proteins that have come
14:49from the diet and trypsin, for example,
14:56comes into play here on this protein.
15:00What was trypsin? It was an
15:02endopeptidase. Where will it break? It
15:06would break in the middle of the
15:08polypeptide. Let's assume it makes a
15:10cut there. There is the trypsin. If
15:17carboxypeptidase comes and works, where
15:18will the carboxypeptidase break? At the
15:22C-terminal end, right? A
15:25carboxypeptidase comes here, it can
15:27break here, it breaks right here. If an
15:32aminopeptidase comes along. Where would
15:35the aminopeptidase break? On this
15:37polypeptide near the amino group. So an
15:41aminopeptidase comes here, breaks this
15:44peptide bond, comes along here, maybe
15:47it can't break here because sometimes
15:50this isn't perfect, and it breaks here
15:53or there. And that way, the digestive
15:57enzymes of the small intestine continue
16:01doing the work of the pepsin. Pepsin
16:04did something, right? It fragmented the
16:07polypeptides into small chains, and now
16:09the small intestine enzymes continue
16:11breaking them down. Let's finish
16:14breaking, for example, this small
16:17peptide. An endopeptidase, a trypsin,
16:20comes and breaks it here. Note that
16:24elastase can also be an endopeptidase.
16:28Elastases are known for digesting
16:30fibrous-type proteins, like elastin,
16:33for example. The point is that an
16:36endopeptidase broke it here, right? An
16:38endopeptidase. A carboxypeptidase comes
16:41and breaks it here. An aminopeptidase
16:46comes along here. On this one, an
16:50endopeptidase comes and breaks it here.
16:54An endopeptidase, it could be a trypsin
16:56, for example. As a product of
16:58digestion, tripeptides and dipeptides
17:00were generated. On the brush border,
17:03there are tripeptidases and
17:04dipeptidases. The tripeptidases break
17:07those tripeptides and generate free
17:10amino acids. The dipeptidases break the
17:13single peptide bond that is here and
17:15generate two amino acids. There are
17:18some tripeptides and dipeptides that do
17:21not break down easily, and for that,
17:23there are transporters that capture
17:25them. And so, little by little, the
17:28polypeptides will break down, and we
17:30will get what interests us, which are
17:32the amino acids. Those amino acids can
17:37be absorbed by enterocytes, and there
17:40are specific transporters. When we have
17:45single, free amino acids, they can pass
17:47through this transporter, a
17:49sodium-dependent transporter that acts
17:52as a symporter because two things pass
17:54at once. This amino acid passes and
17:59sodium passes, right? Very good. What
18:02happens when we have, for example,
18:04fragments that are three amino acids
18:06long, or tripeptides? There are also
18:09transporters. In this case, those
18:11tripeptide or dipeptide transporters
18:14depend on protons. That is why a proton
18:17passes and a tripeptide passes, or a
18:19dipeptide passes. Let's see how this
18:22one passes. For example, look here,
18:24this dipeptide passed, and there we
18:26have it. What we are interested in are
18:28the amino acids. The amino acids can
18:30pass through these transporters in the
18:33basolateral zone and reach the blood,
18:36specifically the hepatic portal vein,
18:38and in this way, these amino acids can
18:41reach the liver. We can continue.
18:44Another amino acid comes, is
18:46transported, comes here, positions
18:48itself, passes along with sodium,
18:50enters, another amino acid comes here,
18:53passes along with sodium, enters, then
18:55passes through the basolateral zone and
18:58reaches the blood. What happens with
19:02the tripeptides and dipeptides? Can
19:05they pass completely into the blood?
19:07Yes, it is possible, but inside the
19:10enterocyte cells, there are peptidases
19:12known as intracellular peptidases that
19:15can break the peptide bonds of these
19:18peptides or tripeptides. For example,
19:20an intracellular peptidase. There it is
19:22. And what happens with those free
19:24amino acids? Now they can pass into the
19:27blood. In the case of this dipeptide,
19:31an intracellular peptidase comes,
19:33breaks it, and we now have free amino
19:35acids. We have seen here that amino
19:41acids from proteins pass into the blood
19:44, but there may be cases where, for
19:46example, we have a polypeptide here; a
19:49carboxypeptidase breaks near the
19:51carboxyl group, but it cannot break
19:54this one, this one, but it can break
19:57this one. Or perhaps it cannot break
20:01this one, it cannot break this one, it
20:03cannot break this one, and that one
20:04either. There it is. A small chain was
20:07generated. This is known as a resistant
20:12peptide that does not digest easily.
20:16There is no problem because these small
20:20peptides can pass via the transcellular
20:23pathway, that is, passing through the
20:28enterocyte membrane to get inside the
20:30enterocyte. Or they can also pass
20:33through the paracellular pathway, that
20:35is, through the sides. It's as if they
20:38were passing through like that, along
20:40the sides of the enterocyte, and they
20:42can finally reach the blood. That is
20:46very important because some peptides—
20:48for example, in milk—can have these
20:50peptides that are generated as a
20:52product of digestion, and they can pass
20:54into the blood and have very important
20:56functions because they can stimulate
20:58many cells. That is why they are called
21:01bioactive peptides. But there can also
21:04be a problem. There are some proteins
21:08in the diet that, when digested,
21:11generate these peptides that can cause
21:14allergies because the immune system can
21:18recognize sequences of this type and
21:21can become altered. It can be altered
21:24as a result of the presence of these
21:26peptides. It has its pros and its cons.
21:31But we will discuss that later when we
21:33talk a bit about food allergies. Well,
21:36that’s all. Any questions, please
21:38leave them in the comments, and until
21:40next time. See you later.

About this transcript

This page contains the full transcript of Digestión de proteínas, absorción y transporte de aminoácidos by Metabolismo, generated from the public captions YouTube serves with the video. The transcript has 2,812 words across 447 segments, with the original timestamps preserved so you can click any line to jump to that moment in the embedded player.

What you can do with it

Use the transcript to take notes, quote the speaker, build a study guide, generate a summary with ChatGPT or Claude via the YouTube Summary tool, or export it as a timed subtitle file with YouTube to SRT. You can also re-open it in the transcriber to choose a caption track available on the video.

Free YouTube transcript tool

YouTube2Text is a free YouTube transcript generator — no signup, no daily limit. Paste any YouTube link and get the full transcript instantly, with timestamps, click-to-jump, caption language selection, AI prompts for ChatGPT, Claude, and Gemini, and exports to TXT, SRT, VTT, or Markdown.