Lipids — Transcript

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1. 0:05Lipids are a group of hydrophobic biomolecules that play
2. 0:09important roles in living organisms.
3. 0:12While the primary function of lipids is long-term energy storage, lipids are also used for protection,
4. 0:19insulation, and lubrication. They also act as precursors for some hormones,
5. 0:25and are a key component of cell membranes.
6. 0:28There are four basic groups of lipids. These are triglycerides,
7. 0:33phospholipids, steroids, and waxes.
8. 0:37Although these groups differ in many respects,
9. 0:40they all have one characteristic in common:
10. 0:43They are all insoluble in water.
11. 0:46You may have noticed that lipids and water do not mix.
12. 0:50For example, notice the yellow colored oil in the beaker of water shown here?
13. 0:56Even if we stirred this for several minutes, or even several hours,
14. 1:00the oil would still separate out from the water. This is because lipids are hydrophobic.
15. 1:07From Latin, the prefix “hydro” means “water” and “phobic” means “fear of”.
16. 1:12So when you hear that lipids are “hydrophobic”, this basically mean that water
17. 1:17and lipids do not mix.
18. 1:20Let’s take a closer look at the category of lipids known as triglycerides.
19. 1:25Triglycerides include the fats and oils. Fats (such as lard and butter) are
20. 1:31solid at room temperature and are used by animals for insulation,
21. 1:35protection and long-term energy storage.
22. 1:38Oils (such as corn oil and olive oil) are liquid at room temperature
23. 1:43and are used by plants for long-term energy storage.
24. 1:47At the molecular level, triglycerides contain two types of subunit molecules:
25. 1:52glycerol and fatty acids. Let’s take a quick look at fatty acids.
26. 1:55Let’s take a quick look at fatty acids.
27. 1:59A fatty acid has three main parts: a chain of carbon and hydrogen atoms called
28. 2:04the “hydrocarbon chain,” a methyl group at one end,
29. 2:08and an acid group at the other end.
30. 2:11Fatty acids can be either saturated or unsaturated.
31. 2:15A fatty acid that has only single carbon to carbon bonds
32. 2:19is known as a saturated fatty acid. This is because the carbon chain is
33. 2:24“saturated” with all the hydrogen atoms it can hold.
34. 2:28Unsaturated fatty acids have one to several double bonds.
35. 2:33Double bonds result in kinks in the
36. 2:35fatty acid chain which affects the melting point of the fat.
37. 2:40Animal fats have saturated fatty acids and are solid
38. 2:44at room temperature while vegetable oils have one or many double
39. 2:48bonds and are liquid at room temperature.
40. 2:51A trans-fat is an example of an unsaturated fatty acid where the hydrogen atoms are on
41. 2:57opposite sides of the double-bond. Trans-fats are usually formed during the production of processed foods
42. 3:04and are also common in partially hydrogenated oils.
43. 3:07In order to increase shelf life and melting point of the fat, excess hydrogen atoms are
44. 3:13introduced to a unsaturated oil. This causes the
45. 3:16formation of trans-fat bonds in the fatty acid chain. Unfortunately the consumption of trans
46. 3:23fats has been associated with cardiovascular disease and its use has fallen from favor.
47. 3:30Now that you understand a little bit fatty acids,
48. 3:33let’s zoom back out and look at how the triglyceride subunits fit together.
49. 3:38Remember, a fatty acid is only a small part of a triglyceride.
50. 3:42To become a triglyceride, 3 separate fatty acids have to
51. 3:46bond with a glycerol molecule through the process of dehydration synthesis.
52. 3:52Let’s move on to the next category of lipids, which is phospholipids.
53. 3:56Phospholipids are similar to triglycerides
54. 4:00in that they contain glycerol and two fatty acids.
55. 4:03What’s different is that a phosphate group rather than a third fatty
56. 4:08is attached to the third carbon of glycerol.
57. 4:12Phospholipids are extremely important, mainly because of their unique properties in regard to water.
58. 4:18The phosphate head of the molecule is hydrophilic (or water-loving).
59. 4:23This means that it mixes well with water. The fatty acid tails, however,
60. 4:27are hydrophobic (or water-hating) and do not mix well with water.
61. 4:33Because of these unique properties, phospholipids tend to arrange themselves so that
62. 4:38only the hydrophilic heads interact with a watery environment,
63. 4:41and the hydrophobic tails crowd inward away from the water.
64. 4:46This structure is the major component of plasma membranes of the cell.
65. 4:52Steroids are the next category of lipids.
66. 4:56Steroids are composed of four fused rings of carbon to which different functional
67. 5:01groups are attached. One well-known steroid
68. 5:04molecule is cholesterol.
69. 5:06Cholesterol serves as a precursor for the synthesis of
70. 5:10other steroids such as testosterone, estrogen, vitamin D, and cortisone.
71. 5:16Cholesterol is present in plasma membranes where it stabilizes the membrane.
72. 5:21The hormones testosterone and estrogen have small differences in their functional groups
73. 5:28but large differences on their effects on an organism.
74. 5:32Waxes are the final group of lipids. Waxes are non-polar and repel water.
75. 5:38They are found in protective coatings on leaves and on outer surfaces of animals.
76. 5:43Wax is produced in the ears of some animals to protect the eardrum.
77. 5:48In addition, bees construct honey combs from wax.
78. 5:52Now that we’ve covered all four categories of lipids, Let’s do a quick recap.
79. 5:57The four categories of lipids are triglycerides, phospholipids,
80. 6:01steroids and waxes. All lipids are insoluble in water.
81. 6:07While the primary function of lipids is long-term energy storage,
82. 6:11lipids are also used for a multitude of other purposes, such as protection
83. 6:15and insulation, and as key component of hormones and cell membranes.