12. Oxidation of one mole of acetyl-CoA via the citric acid cycle results in : A

Question

12. Oxidation of one mole of acetyl-CoA via the citric acid cycle results in : A. production of one mole of citrate. B. consumption of one mole of oxaloacetate. C. production of 7 moles of ATP. D. production of 2 moles of CO2 E. production of one mole of succinate. 13. Entry of acetyl-CoA into the citric acid cycle is decreased when: A. the ratio of [ATP] [ADP] is high. B. [AMP] is high. C. the ratio of [NAD+] [NADH] is high. D. NADH is rapidly oxidized through the respiratory chain E. none of the above.

Explanation / Answer

Ans. #12. Correct option- D. Production of 2 mol of CO2.

Being cyclic in nature, there is NO NET production/gain of 1 mol of citrate, succinate of oxaloacetate when acetyl-CoA enters TCA cycle.

# However, there is NET production of 2 mol CO2 when 1 mol acetyl-CoA enters the TCA cycle.

# 1 mol acetyl-CoA produces 1 GTP through substrate level phosphorylation, 3 NADH and 1 FADH2 during TCA. 3 NADH and 1 FADH2 forms 9 ATP through ETC and subsequent oxidative phosphorylation.

#14. Correct option- A. The ratio of [ATP] / [ADP] is high.

# A high [ATP] / [ADP] ratio inactivates pyruvate dehydrogenase (PDH) complex by phosphorylating it. Inactivation of PDH complex reduces the availability of acetyl-CoA to TCA, and thus reduces the rate of TCA cycle.

# High [AMP] increases the rate of TCA yield.

# NAD+ is used as cofactors for three enzymes of TCA cycle. So, a higher [NAD+] / [NADH] ration increases TCA rate.

# Rapid oxidation of NADH increases the availability of NAD+ to the TCA enzymes, thus increases the rate of TCA cycle.

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