Question

5. Yeast engage in alcoholic fermentation in order to a. provide brewers with a steady source of income b. produce NADH from NAD+ to allow glycolysis to operate anaerobically c. produce acetyl Co A for entry into the TCA cycle when oxygen is absent d. produce ATP from pyruvate e. none of the above

Answer 1

Answer: Option d. Produce ATP from Pyruvate

Fermentation in yeast occurs in the following steps:

1. Formation of acetaldehyde: Pyruvic acid which is produced from glycolysis, is converted to acetaldehyde with the loss of carbondioxide.

2. Reduction of acetaldehyde to ethylalcohol: Thus formed acetaldehyde undergoes reduction to form ethylalcohol during which NADH is converted(oxidised) to NAD+

3. Generation of ATP: NAD+ produced in the previous step, helps glycolysis to proceed even in the absence of oxygen to supply ATP.

Now, looking at the options, we have:

a. provide brewers with a steady source of income. This CANNOT be TRUE, although we are benefitted from the yeast fermentation, this is only our exploitation but not true from the perspective of yeast as it part of its metabolic process and does not engage in alcoholic fermentation for our sake

b. produce NADH from NAD+ to allow glycolysis to operate anaerobically. As mentioned above in the second step, NADH is utilised to form NAD+ but not the reverse. So that makes this option also to be false

c. produce acetyl Co A for entry into the TCA cycle when oxygen is absent. This is also false, because, generation of acetyl coA occurs when pyruvic acid is oxidised i.e., in the presence of oxygen. Fermentation is an anerobic process and pyruvate is reduced, and NADH is oxidised to produce NAD+

d. produce ATP from pyruvate is TRUE, as mentioned in the 3rd step above

e. Since option d is correct, option e. None of the above cannot be true.