Lecture 11-05 - Lecture 11-05-Ch 14 Fat=...

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Lecture 11-05-Ch. 14 Fat= triacylglyerols=TAGs 5-25% body weight is fat o 90% is TAGs ; rest is cholesterol and other types of lipids fat storage cells are adipocytes-"giant" fat globules primarily energy storage, but also serve as o "cushioning" for internal organs o insulation for cold Metabolic Reserves in ~70 kg person Available energy (kcal) from: Tissue glucose/glycogen TAG Protein Blood 60 45 0 Liver 400 450 400 Brain 8 0 0 Skeletal Muscle 1200 450 24,000 Adipose 80 135,000 40 the carbon atoms in TAGs are more reduced, so they release higher energy yield when oxidized TAGS release twice as much energy per weight compared to glycogen (due to water content) brain does not generally use fat except in periods of extreme starvation--a lipid class called ketone bodies Metabolism also produces water-- remember the goal is to go to carbon dioxide and water-- this is known as "metabolic water" fat produces ~107 grams of water per 100 g; protein ~40 grams; carbohydrate ~55g desert animals rely on metabolic
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water-- camels hump is fat deposit as a source of metabolic water migrating birds rely on metabolic water during non-stop flights humans obtain only about 8-10% of their water needs via metabolic water Mobilization of Stored Fat transport of fat to storage is not regulated , it is all delivered to the adipocytes: hydrolyzed to FAs, transported across membrane and resynthesized as TAGs for storage o what you eat and do not burn up-- is what you store as fat ........................ all that Halloween candy ........ however, release is regulated by hormone stimulus o epinephrine during stress o glucagon during fasting turns on signal cascade--turns on triacylglycerol lipases by phosphorylation (see fatty acid metabolism) --more in chapter 16! Lipases--releases FA from TAGs or phospholipids specific sites of hydrolysis components of spider and snake venom
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Transport of FA-CoA to mitochondria must move into mitochondria for oxidation to occur o carrier--carnitine covalently linked to acyl- FA for transport o acyltransferase--attaches carnitine in place of CoA-- located on outer surface of inner membrane translocase moves carnityl-fatty acid across membrane converted back to fatty acyl-CoA on other side of membrane by acyltransferase separate pools of CoA in cytosol and mitochondria
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fatty acyl-CoA synthetases catalyze activation reaction: 2 step mechanism to form fatty acyl-CoAs o activation of carboxyl group by ATP o thiol group of CoA displaces AMP to form fatty acyl-CoA--thioester o very similar mechanism to activation of amino acids for protein synthesis o reaction pulled to right by hydrolysis of PPi (where have we seen this before?) the PPi counts as two ATP equivalents, it takes 2 ATP to regenerate the AMP back to ATP three types of synthetases: found on outer mitochonria membrane o long chain--10-20 carbons o medium chain--4-12 carbons o short chain--2-3 carbons (acetate and propionate)
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Overall reaction for oxidation of palmitoyl CoA to generate energy palmitoyl CoA (16 carbons) + 23O 2 + 106 ADP + 106
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