Topic 6 Part B BIO188 F09 1pp

Topic 6 Part B BIO188 F09 1pp - How Cells Harvest Energy...

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1 How Cells Harvest Energy Topic 6 Part B
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2 Oxidation of Pyruvate In the presence of oxygen pyruvate transported from cytoplasm to mitochondria Within mitochondria , pyruvate is oxidized in a single decarboxylation reaction, yielding acetyl-CoA, NADH, and CO 2 . CYTOSOL MITOCHONDRION NAD + NADH + H + 2 1 3 Pyruvate Transport protein CO 2 Coenzyme A Acetyl CoA
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3 Oxidation of Pyruvate Pyruvate dehydrogenase = 60 subunit multi-enzyme complex Net reaction: Pyruvate + NAD + + CoA --> Acetyl-CoA + NADH + CO 2 Breakdown of proteins, fats and other lipids generate acetyl-CoA Acetyl-CoA goes to either energy production (ATP) OR energy storage (lipid synthesis) Dependent on cellular ATP levels
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4 Stage Two - Krebs Cycle Acetyl-CoA is oxidized in a series of 8 reactions = the Krebs cycle (also called citric acid cycle or tricarboxylic acid cycle) Occurs in matrix of mitochondria 1) priming - 2 reactions create 6- energy extraction 2) energy extraction - 2 oxidation reactions + 1 substrate-level phosphorylation of ATP 3) More oxidation reactions (energy extraction) and regeneration of starting material
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6 Krebs Cycle Acetyl CoA CoA—SH Citrate H 2 O Isocitrate NAD + NADH + H + C O 2 ! -Keto- glutarate CoA—SH C O 2 NAD + NADH + H + Succinyl CoA CoA—SH P i GTP GDP ADP ATP Succinate FAD FADH 2 Fumarate Citric acid cycle H 2 O Malate Oxaloacetate NADH +H + NAD + 1 2 3 4 5 6 7 8 Generates 2 ATP molecules per 1 glucose Harvest electrons for electron transport chain Releases CO 2
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7 Energy Production By Krebs Cycle Energy production per acetyl-CoA: 1x ATP 3x NADH 1x FADH 2 (another electron acceptor) But remember, 2 cycles per glucose molecule Lots of electron carriers, but not much ATP Currently net 4 ATP (2 glycolysis + 2 Krebs = 4)
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8 Stage Three: The Electron Transport Chain 2 molecules carry electrons to the inner mitochondrial membrane , where they transfer electrons to a series of membrane-associated proteins electron transport chain is in cristae of mitochondrion Most of the chain’s components are proteins, which exist in multiprotein complexes The carriers alternate reduced and oxidized states as they accept and donate electrons The final electron acceptor is O 2 forming H 2 O: O 2 + 4 H + + 4 e - --> 2 H 2 O OR 1/2 O 2 + 2 H + + 2 e - --> H 2 O
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Topic 6 Part B BIO188 F09 1pp - How Cells Harvest Energy...

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