Fat Breakdown and Synthesis

00:01 They've indicated in previous lectures, the lipids are incredibly diverse set of molecules but as we will see they have very common roots and a very simple molecule.

00:10 In this lecture, I'll start that process by talking about fat and fatty acid metabolism.

00:15 Now, fat metabolism is something that all of us wanna do, if we can -- if we're worried too much about how much we're carrying around.

00:21 First, I wanna talk about fat breakdown.

00:23 Fats and oils are as we've seen triglycerides and fat is stored in our body in specialized cells called adipocytes.

00:31 The fat is important to travel in our blood stream but it's also a difficult way to travel because it's not water soluble where is our blood actually is mostly aqueous solution.

00:41 To travel in the bloodstream fat must go through complexes called lipoprotein complexes and you probably know them as LDLs and chylomicrons.

00:50 Fats are broken down into fatty acids and glycerol, it's constituents -- constituents components.

00:56 By action of enzymes called lipases.

00:59 You can see on the screen a typical fat molecule.

01:03 It has a glycerol backbone is shown here and you can see Ester bonds between all the fatty acids and the glycerol.

01:09 Now, each of those individuals fatty acids are targets of action of different lipases.

01:14 The first one is shown at the top is a targeted enzyme known as hormone sensitive lipase and it will cleave only the first fatty acid.

01:23 The second fatty acid was cleaved by an enzyme called diacyglycerol lipase.

01:28 The third enzyme is cleaved off by an enzyme called monocyglycerol lipase.

01:33 The product of that is glycerol molecule and three fatty acids.

01:37 If we're moving to make a fat then, it's not the simple reversal of the process although it's similar.

01:43 The starting point for this synthesis of a fat is not glycerol but glycerol-3-phosphate as you can see on the screen.

01:50 In the first step of the reaction glycerol-3-phosphate is converted into a molecule called lysophosphatidic acid, and that simply is a glycerol-3-phosphate that had a fatty acid attached to position 1 by an enzyme called acyltransferase 1.

02:06 A similar reaction adds the second fatty acid as you can see here by an enzyme called acyltransferase 2.

02:14 At this point, we have a molecule called phosphatidic acid and as we will see phosphatidic acid is a branch point in the synthesis of other lipids.

02:23 Now, the fatty acid in phosphatidic acid are usually saturated at position 1.

02:29 Meaning all single bonds and usually unsaturated at position two meaning having one or more double bonds.

02:37 Phosphatidic acid can be convert into fat in only two more steps.

02:42 First, the phosphate part of phosphatidic acid is removed by a phosphatase as you can see here.

02:48 That leaves behind a molecule called diacylglcyerol.

02:51 Diacylglcyerol is converted into a triacylgcyerol which is either a fat or an oil by the enzyme acyltransferase 3.

03:00 Now, whether something as a fat or an oil depends upon whether or not it is a solid room temperature a fat or a liquid at room temperature called an oil.

03:10 Chemically the differences between these two are not very significant.

03:13 They arise from the composition of the fatty acids within the fat.

03:17 A fat is a molecule that contains mostly saturated bonds and therefore is what gives of the property being a solid at room temperature.

03:27 And oil on the other hand has a considerable amount of unsaturated bond within it and results in being a liquid at room temperature.