Which of the following must be regenerated for glycolysis to proceed?

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BlackTom AI · Accepted Answer

The question asks which factor must be regenerated for glycolysis to continue functioning.
Option 1: pyruvate. While pyruvate is the end product of glycolysis under anaerobic conditions or the substrate for further pathways, its formation does not itself regulate the ongoing need for glycolysis to proceed. Pyruvate accumulation does not block the glycolytic steps that follow; rather, its fate is downstream of glycolysis.
Option 2: ATP. Glycolysis uses ATP in the early steps (investment phase) and later produces ATP (payoff phase). Although ATP levels influence the rate of glycolysis, the process can continue as long as substrates are available and there is sufficient catalytic activity; there is no absolute requirement that ATP be regenerated to allow the pathway to proceed, since the pathway both consumes and generates ATP during flux.
Option 3: NAD+. The oxidation step catalyzed by glyceraldehyde-3-phosphate dehydrogenase converts glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate and, in doing so, reduces NAD+ to NADH. For glycolysis to keep moving, NAD+ must be regenerated from NADH; otherwise, this dehydrogenase step would halt and upstream intermediates would accumulate. Regeneration of NAD+ occurs via fermentation under anaerobic conditions or via the mitochondrial electron transport chain under aerobic conditions, sustaining continuous glycolytic flux.
Option 4: UDP-glucose. UDP-glucose is a nucleotide-sugar involved in biosynthetic pathways such as glycogen synthesis, not in the core glycolytic sequence. It does not regulate or directly participate in maintaining glycolytic throughput.
In summary, among the options, only the regeneration of NAD+ is functionally essential to keep glycolysis progressing, because it replenishes the cofactor needed for the glyceraldehyde-3-phosphate dehydrogenase step and thus prevents a bottleneck in the pathway.

Which of the following must be regenerated for glycolysis to proceed?

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