Question

Metabolic fate of pyruvic acid depend on
(a) Cellular energy
(b) Availability of oxygen
(c) Type of respiration
(d) All of the above

Answer 1

Hint: It is a versatile molecule that feeds into various pathways. After glycolysis, it can be converted to acetyl- CoA, which has numerous metabolic destinations, including the TCA cycle. Pyruvate can also be converted into lactate, which enters the Cori cycle in absence of mitochondria or oxygen.

Complete answer:
Pyruvate, the end product of glycolysis, must be further metabolized to maintain proper redox balance. The metabolic fate of pyruvic acid depends on cellular energy, availability of oxygen, and type of respiration.
- Under aerobic conditions, acetyl- CoA is produced which is the starting material for the TCA cycle and the pyruvate dehydrogenase complex plays an important role in this catalysis step.
- Under anaerobic conditions, pyruvate is reduced to lactic acid in a reaction catalyzed∙ by the lactate dehydrogenase enzyme. During this reduction step, NAD+ is formed from NADH. Such reactions are observed in the muscle cells that are devoid of oxygen and microbes like lactic acid bacteria.
- Microorganisms including yeast opt for fermentation of sugars to ethanol via glycolysis in a two- step process.
Pyruvate is converted to acetaldehyde in the presence of Thiamine pyrophosphate and Mg2+ and a reaction catalyzed by enzyme pyruvate decarboxylase.
Acetaldehyde is further reduced to ethanol by NADH and this reaction catalyzed by enzyme alcohol dehydrogenase.
So, the correct answer is all of the above.

Note: Glycolysis can be defined as the sequence of reactions for the breakdown of Glucose (a 6- carbon molecule) to two molecules of pyruvic acid (a 3- carbon molecule) under aerobic conditions, or lactate under anaerobic conditions along with the production of a small amount of energy. It is a sequence of ten enzyme- catalyzed reactions for cellular respiration.