Final answer:
Muscle cells keep glycolysis running by recycling NAD+ through the transfer of electrons to it, forming NADH. In anaerobic conditions, this occurs through lactic acid fermentation, allowing for the continual production of ATP.
Step-by-step explanation:
To keep glycolysis going, muscle cells must recycle their supply of NAD+ (nicotinamide adenine diphosphate), by transferring electrons to it, forming NADH. Glycolysis is an anaerobic process that occurs in the cytoplasm and serves as the initial step in cellular respiration. It converts glucose into pyruvate, generating a small amount of ATP (Adenosine Triphosphate) and NADH in the process. If oxygen is present, NADH can be used in oxidative phosphorylation to generate more ATP. Without oxygen, as in muscle cells during intense exercise, the cell resorts to fermentation to regenerate NAD+ from NADH, allowing glycolysis to continue.
In the case of human muscle cells under anaerobic conditions, this is achieved through lactic acid fermentation. Here, NADH transfers its electrons to pyruvate, transforming it into lactic acid. This step is vital for regenerating NAD+ so that glycolysis can maintain the production of ATP, even when oxygen is scarce.