What is the primary function of pyruvate kinase in glycolysis?

The primary function of pyruvate kinase in glycolysis is to catalyze the conversion of phosphoenolpyruvate (PEP) to pyruvate, simultaneously facilitating the transfer of a phosphate group from PEP to ADP, which results in the formation of ATP. This process is a key example of substrate-level phosphorylation, where a high-energy phosphate group is directly transferred to ADP to synthesize ATP, independent of oxidative phosphorylation.

This reaction is significant because it represents one of the final steps in glycolysis, yielding energy in the form of ATP, which is essential for cellular functions. Pyruvate kinase is often regulated by various metabolites and signaling molecules, which allows the cell to control the flow of carbon through glycolysis based on its energy needs.

The other options represent processes that are not directly related to pyruvate kinase's role in glycolysis. For instance, while glucose is converted into ATP through glycolysis, it is a broader description that encompasses multiple enzymatic steps rather than a specific function of pyruvate kinase. The regeneration of NAD+ is critical for glycolysis but is primarily managed by dehydrogenase enzymes earlier in the pathway. The cleavage of fructose into smaller molecules pertains to different metabolic pathways and does