Chemotrophic Energy Metabolism: Aerobic Respiration I

1
Chemotrophic Energy Metabolism Aerobic
Respiration I

• Reading Becker, ch. 14, pp. 404-

2
Aerobic Respiration
3
2 Ways to Produce Acetyl CoA in the Mitochondrion

• Oxidative Decarboxylation of pyruvate to acetate
• Esterification of acetate to coenzyme A
• O O O
  
• H3C C C O- H3C C 0-
• Fatty acids are esterified to coenzyme A
• Fatty acids are oxidized to produce acetyl CoA

oxidative decarboxylation
pyruvate dehydrogenase
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Esterification of Acetate to Coenzyme A

• Sulfhydryl group (thiol group) forms a thioester
  bond with acetate
• Coenzyme A is now acetylated and is referred to
  as acetyl CoA

5
TCA Cycle

• TCA Cycle Citric Acid Cycle Krebs Cycle
• TCA (TriCarboxylic Acid)
• produces citrate (aka citric acid) as an
  intermediate in the cycle
• citrate is a tricarboxylic acid

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Condensed Version of the TCA Cycle

• 2C acyl group from acetyl CoA 4C oxaloacetate ?
  6C citrate
• Citrate ? 4C oxaloacetate
• 2 CO2
• 3 NADH
• 1 FADH
• 1 ATP
• FAD flavin adenine dinucleotide
• reduced form FADH

Reduced coenzymes
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Per Glucose Yield of the TCA Cycle

• 2 ATP
• 6 NADH
• 2 FADH

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Allosteric Regulation of the TCA Cycle

• Activators of acetyl CoA formation
• CoA, NAD, AMP
• Inhibitors of acetyl CoA formation
• Acetyl CoA, NADH, ATP
• Activators of TCA reactions
• ADP
• Inhibitors of TCA reactions
• NADH

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Fat As An Energy Source For Cells
Glycerol enters the glycolytic pathway as
dihydroxyacetone phosphate!
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b-Oxidation of Fatty Acids
Fatty acids become esterified to coenzyme A by
forming a thioester bond with the reactive
sulfhydryl group. Subsequent fatty acid
oxidation forms acetyl CoA. 2 carbons from the
fatty acid remain attached to CoA, and the
liberated fatty acid chain is now 2 carbons
shorter. Liberated fatty acid can become
esterified to another molecule of CoA for another
round of b-oxidation.