A yeast cell and a muscle cell both ferment glucose…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A yeast cell and a muscle cell both ferment glucose.
- In each cell, which compound is reduced by NADH, and which compound is oxidised?
- Why does glycolysis stop if fermentation is blocked and there is no oxygen?
- A mutant yeast has no pyruvic acid decarboxylase. What happens to its alcoholic fermentation?
Need a reminder? The key ideaShow
Without oxygen, pyruvic acid takes the hydrogen of NADH, and NAD is made again. Alcoholic fermentation: pyruvic acid decarboxylase gives acetaldehyde and carbon dioxide, then alcohol dehydrogenase gives ethanol. Lactic acid fermentation: lactate dehydrogenase gives lactic acid and no carbon dioxide. The net gain is ATP for each glucose.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. (a) In yeast, acetaldehyde is reduced to ethanol. In muscle, pyruvic acid is reduced to lactic acid. In both, NADH is oxidised to NAD.
Step 2. (b) Glycolysis needs NAD to oxidise PGAL. Without fermentation, all the NAD turns into NADH, and glycolysis stops.
Step 3. (c) The first step, pyruvic acid to acetaldehyde, cannot happen. No acetaldehyde is made, so the NADH is not oxidised and alcoholic fermentation stops.
Answer: (a) acetaldehyde in yeast, pyruvic acid in muscle, with NADH oxidised; (b) no NAD is left; (c) it stops.
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