Leyland 7 stage III catabolism citric acid cycle

Question 1

reactions of cellular respiration

Answer 1

• citric acid cycle removes electrons from acetyl CoA => NADH & FADH2
• reoxidation of NADH &FADH2 in oxidative phosphorylation => ATP

Question 2

Pyruvate dehydrogenase

Answer 2

is the link between glycolysis & citric acid cycle

• mitochondrial matrix
• large, multi-subunit enzyme

Pyruvate -> acetyl -CoA

Question 3

Citric acid cycle

Answer 3

Irreversible reaction

• mitochondrial matrix
• oxidises 2-carbon molecules to produce ATP, NADH, FADH2 and CO2

Question 4

Citric acid cycle

equation

Answer 4

CH3CO~CoA + 3NAD+ + FAD + GDP + Pi + 2H2O à

2CO2 + CoA + 3NADH + 3H+ + FAD2H + GTP

Question 5

Isocitrate dehydrogenase

Answer 5

1
• Oxidative decarboxylation to produce NADH and CO2
• Allosterically regulated

Isocitrate -> ketoglutarate

Question 6

a-ketoglutarate dehydrogenase

Answer 6

2
• Oxidative decarboxylation to produce NADH and CO2
• Product inhibition by NADH and succinyl CoA

a-ketoglutarate -> succinyl CoA

Question 7

Regulation of the citric acid cycle

Answer 7

amphibolic

• ATP / ADP ratio
• NAD+ / NADH ratio
• Allosteric regulation
• Product inhibition
• Substrate availability
• Intermediates can be withdrawn for biosynthetic pathways
• Anaplerotic reactions – top up the pathway to allow continuation

Question 8

citric acid cycle - summary

Answer 8

• Central pathway in the catabolism of carbohydrates, lipids, proteins

• Mitochondrial
• Oxidative producing NADH & FAD2H
• Some energy as GTP (=ATP) produced directly
• Breaks C-C bond in acetate (acetyl~CoA) oxidising to CO2
• Produces precursors for biosynthesis
• Does not function in absence of O2
• Genetic defects of citric acid cycle enzymes are very rare