Question

During cellular respiration, the first step is glycolysis where the glucose is split into 2 pyruvates, 2 NADH, and 2 ATP. The pyruvate either goes through the citric acid cycle or goes through lactic acid fermentation. If you remove the citric acid cycle and fermentation, is there a specific way to reduce pyruvate? I am relatively new to chemistry and I was wondering if pyruvate can either store additional electrons or if it can get reduced to another substance and collect additional electrons. If pyruvate doesn't get reduced in any scenario, can ATP get reduced?

Answer 1

Pyruvate can be reduced to acetyl CoA, which enters the citric acid cycle, or to lactate during fermentation. ATP is not directly reduced; it is generated by the electron transport chain's use of high-energy electrons from NADH or FADH2. Without the citric acid cycle or fermentation, cells cannot efficiently recycle NADH, needed for ongoing glycolysis.

Step-by-step explanation:

During cellular respiration, pyruvate, which is produced from glucose during glycolysis, can undergo different fates depending on the presence of oxygen. In an aerobic environment, pyruvate is converted into acetyl CoA and enters the citric acid cycle, also known as the Krebs cycle or tricarboxylic acid cycle, where it is fully oxidized to produce ATP, NADH, FADH2, and CO2. However, if the citric acid cycle is removed, pyruvate may be chemically reduced through alternative metabolic pathways, such as through the action of the enzyme lactate dehydrogenase during fermentation, where it is converted into lactate. ATP itself is not directly reduced; instead, it is the high-energy currency of the cell and is produced when NADH and FADH2 donate electrons to the electron transport chain.

Specifically, during the conversion of pyruvate to acetyl CoA, a molecule of CO2 is released, and high-energy electrons are transferred to NAD+, reducing it to NADH. This NADH then carries electrons to the electron transport chain for ATP production. Without the citric acid cycle or fermentation, cells lack the mechanisms to efficiently recycle NADH back to NAD+, which is required for glycolysis to continue. Alternative chemical reactions to reduce pyruvate might exist in a laboratory setting, but in biological systems, the pathways described are crucial.