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Succinyl-CoA
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Fatty Acid Metabolism
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Phospholipase A 1 Phospholipase A 2 Phospholipase A 1
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FADH 2
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Glycerol = GAP + NADH - ATP If: GAP = 2 ATP + NADH + Acetyl-CoA Then: glycerol = Acetyl-CoA + 2 NADH + ATP If: Acetyl-CoA = 3 NADH + FADH 2 + GTP Then: glycerol = 5 NADH + GTP + ATP + FADH 2 If: NADH = 3 ATP, FADH 2 = 2 ATP and GTP = ATP Then: glycerol = 19 ATP
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1 NADH is converted to FADH 2 : 1 less ATP
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Fatty acid + CoA + ATP ---> Fatty acyl-CoA + AMP + PP i AMP + ATP ---> 2 ADP ADP + P i ---> ATP You essentially consume 2 ATP to activate FFAs
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Claisen cleavage reaction: reverse of citrate synthase
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Thiolase
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For a saturated fatty acid with n carbon atoms (even number) You make n/2 Acetyl-CoA, which enter TCA cycle to yield n-2/2 NADH n-2/2 FADH 2 -oxidation yields 3n/2 NADH n/2 FADH 2 n/2 ATP 3ATP per NADH 2ATP per FADH 2 Cn:0 yields (n-2/2 + 3n/2)3ATP + (n-2/2 + n/2)2ATP + n/2 ATP - 2ATP Lost in activation
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What about unsaturated fatty acids?
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For every double bond an odd number of carbons away from carbonyl: 3 round -oxidation Attempt 4th round Doesn’t work
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Ready for another round of oxidation: however no FADH 2 produced. This ultimately costs 2 ATP in the end.
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For every double bond an even number of carbons away from carbonyl: Neither dehydrogenase nor isomerase recognize ∆4 unsaturated fatty acids as a substrate. 5 rounds -oxidation
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Just reduce the double bond Resume oxidation with the cost of 1 NADPH which ultimately costs one NADH and 3 ATP in the end.
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What about fatty acids with odd number carbons Last round produces propionyl-CoA instead of Acetyl-CoA
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One extra ATP is consumed to convert propionyl-CoA to succinyl- CoA For odd chain fatty acids You make n-3 Acetyl-CoA and one propionyl-CoA Succinyl-CoA enters TCA cycle This is can be used as an anapleurotic rxn or the succinyl-CoA can be converted to malate. In the latter case.....
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Conversion of succinyl-CoA to malate makes 1 ATP, 1 FADH 2
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Malate pyruvate +1 NADPH 4 NADH + 1 FADH 2 + ATP Malic enzyme - decarboxylating
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One extra ATP is consumed to convert propionyl-CoA to succinyl- CoA So.....for odd chain fatty acids You make n-3 Acetyl-CoA and one propionyl-CoA One ATP and one FADH 2 are made to convert succinyl-CoA into malate One NADPH is made converting malate into pyruvate Pyruvate = 4 NADH, 1 ATP and 1 FADH 2 So….propionyl-CoA = 2 FADH 2 + 4 NADH + 1ATP + NADPH Cn(odd):0 yields (n-3/2 + 3n-3/2 + 4)3ATP + (n-3/2 + n-3/2 + 2)2ATP + (n-3/2 + 1) ATP - 2ATP + NADPH
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The glyoxosome is a special peroxisome in germinating seeds that uses Acetyl-CoA from triacylglycerol to make glucose
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-oxidation: in the ER
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-oxidation: peroxisome
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Ketone Bodies Liver Muscle
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Lipid Biosynthesis Reversing fatty acid catabolism. What steps are different?
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Starts with malonyl-CoA instead of acetyl-CoA
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Cost = (n-2)ATP + 2(n-2)NADPH
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Fatty Acid Synthase Ketoacyl-ACP Synthase Malonyl-CoA-ACP transferase Ketoacyl-ACP reductase Hydroxyacyl-ACP dehydratase Enoyl-ACP reductase Acetyl-CoA-ACP transacetylase ACP = acyl carrier protein
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Fatty acid biosynthesis occurs in cytosol Acetyl-CoA is made in the mitochondrion
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Fatty acid desaturases are oxidases
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Much of the fatty acids release by adipocytes is taken up by tissues and coverted to energy. This is triggered by low glucose by glucagon or epinephrine Much is reconverted into triacylglycerol by the liver and released
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Glucagon tells the liver to stop glycolysis and make glucose How then do you get glycerol?
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Glucocorticoids stimulate fatty acid release from adipose tissue
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What cofactor would you use?
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What cofactor?
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Desaturase In plants and yeast there is hydroxylation instead of desaturation
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Heme generated tyrosine radical abstracts this proton
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How is the radical generated in the first place?
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Flavin monooxygenase
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Dihydrocholesterol 1 25-dihydroxycholecalciferol Cholecalciferol Vitamin D 3
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