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Lecture 20

Lecture 20: "Fatty Acids, Ketone Bodies & Biosynthesis"

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Western University
Biochemistry 2280A
Mel Usselman

Biochemistry Lecture No. 20: Fatty Acids, Ketone Bodies & Biosynthesis th Thursday October 25 , 2012 Triacylglycerol Breakdown: -Triacylglycerol breakdown commences in adipocytes (fat storage cells) under low glucose conditions where hormone-insensitive lipase removes glycerol from fatty acids. This action results in fatty acids and glycerol as products. Fatty acids go the liver and muscles (not the brain, it is looking for glucose) and are converted to acetyl CoA via β-oxidation. Glycerol molecules go to the liver and are fuel for gluconeogenesis. Activation Of Fatty Acids In The Cytosol: -Coenzyme A helps fatty acids cross the inner mitochondrial membrane (fatty acyl-CoA is transported into the mitochondrial matrix). This reaction requires the use of both the ϒ and β phosphates (uses as much energy as possible), but is a good energy investment in the long run. The high energy sulphur bond in acyl-CoA is also a notable quality of the molecule. β-Oxidation Of Fatty Acids In The Matrix: -Note that “acyl” is a prefix for what is left over after the fatty acid joins to CoA. In the β-oxidation of fatty acids, 2 carbons are being cleaved after each turn of the Citric Acid Cycle. This process makes FADH a2d NADH (reduction), which in turn donate electrons to the electron transport chain. The liver will also take the acetyl CoA and use it for its energy needs. The fatty acids are more condensed (more rich) forms of energy and thus, are more valuable in one molecule as opposed to one molecule of glucose. -The oxidation of unsaturated fatty acids yields fewer FADH and may consume NADPH in the process. 2 The awkwardness of the double bonds in unsaturated fatty acids is why saturated fatty acids yield much more in terms of electron carriers. However, the oxidation of “odd-chain” fatty acids yields one propionyl-CoA (3-carbon unit), which enters the Citric Acid cycle as succinyl-CoA. Different Sources Of FADH : 2 -Whether from the Citric Acid Cycle, cytosolic NADH, or from fatty acid oxidation, all FADH molec2les funnel their electrons into coenzyme Q to make QH (but 2sing different protein complexes). Each FADH m2lecule is worth 1.5 ATP. Ketone Bodies: -Ketone bodies are the method of
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