Pyruvate, the end-product of glycolysis, has several metabolic fates depending o

Question

Pyruvate, the end-product of glycolysis, has several metabolic fates depending on the type of tissue and its physiological state. For example, skeletal muscle driven to the anaerobic threshold through intense activity shows high rates of lactate formation. The relevant chemical reaction is shown below:

Pyruvate + NADH + H+ ? Lactate + NAD+

When O2 is limiting, glycogen becomes the primary source of ATP for skeletal muscle. Which step in glycolysis (reference its number) becomes dependent on pyruvate to lactate conversion under O2 limiting conditions, and briefly explain why?

Explanation / Answer

In aerobic conditions, NADH is oxidized to NAD+ via ETC.

Pyruvate is converted to lactate in the absence of oxygen. This step regenerates NAD+ which is required for the continuous occurrence of glycolysis.

Pyruvate + NADH + H+ --------> Lactate + NAD+

In glycolysis, the conversion of G-3-P to 1,3-BPG requires NAD+.

G-3-P + NAD+ + Pi ------> 1,3-BPG

So, this step of glycolysis is dependent on fermentation.

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