Question

How many ATPs are obtained from the catabolism of 3 molecules of glucose under anaerobic conditions via substrate level phosphorylation?

Please say how you got the number!

Answer 1

This is the balance sheet for cellular respiration taking place in the presence of oxygen.

Anaerobic respiration occur in the absence of oxygen. The only two processes in anaerobic respiration are glycolysis and fermentation. There is no ATP production in fermentation. So in the given balance sheet you need to focus only on glycolysis.

You can see that 4 molecules of ATP are synthesized and 2 molecules of ATP are consumed in glycolysis. You just have to focus on direct synthesis of ATP because this is substrate level phosphorylation. So the net production of ATP in one round of glycolysis by substrate level phosphorylation will be 2 molecules.

Oxidative phosphorylation occurs when ATP production takes place by NADH and FADH_2.

So, two molecules of ATP are produced in anaerobic respiration by substrate level phosphorylation. So, 3 molecules of glucose will produce 2 × 3 = 6 molecules of ATP.

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