Question

Louis Pasteur observed that when oxygen is introduced to cells consuming glucose at a high rate in an anaerobic environment, fermentation ceases and the rate of glucose consumption decreases. This phenomenon is called the Pasteur effect. The basis of this effect is the shift from fermentation to oxidative phosphorylation to regenerate NAD*. Additionally, the cells also synthesize ATP through oxidative phosphorylation. In respiration-deficient yeast mutants that lack cytochrome oxidase, the Pasteur effect is not seen. Select the reasons why the absence of cytochrome oxidase eliminates the Pasteur effect. Without cytochrome oxidase, the respiratory chain will be inhibited and the mutant yeast cells will be unable to transfer electrons from NADH to oxygen. In the absence of an active respiratory chain, yeast cells will continue to regenerate NAD* for glycolysis via fermentation. In the absence of cytochrome oxidase, the mutant yeast cells will be unable to produce ATP through oxidative phosphorylation. Low ATP levels will maintain the high rate of glucose consumption in the mutant yeast cells. In the absence of cytochrome oxidase, the last step in the respiratory chain will be inhibited, thus reducing the amount of ATP produced by oxidative phosphorylation. The mutant cells with compensate for the decrease in ATP production by generating ATP via fermentation Without cytochrome oxidase, the mutant yeast cells will be unable to repenerate NAD", thus inhibiting glycolysis. When glycolysis is inhibited, cells will continue to break down glucose at a much faster rate via fermentation In the absence of cytochrome oxidase, the respiratory chain will be inhibited and NADH will accumulate. Since NADH is a substrate for glycolysis, high NADH levels will maintain the high rate of glucose consumption.

Answer 1

Answer: Option C is correct
Description:
Glycolysis produces 2 ATP and 2 NADH.
NAD+ is a substrate for Glycolysis.
In the presence of oxygen, NADH is utilized in ETC to produce ATP and is regenerated back to NAD+. So, Glycolysis can continuously occur.
However, ETC cannot function in the absence of oxygen. So, NAD+ is regenerated by fermentation.

Cytochrome oxidase is a component of the electron transport chain (ETC). If Cytochrome oxidase is mutated, cells cannot perform ETC even in the presence of oxygen.