Final answer:
Glycolysis is a sequence of reactions that convert glucose into pyruvate, yielding a net gain of 2 ATP and 2 NADH per glucose molecule. It begins with an energy investment phase and ends with an energy payoff phase, with the net ATP result arising from substrate-level phosphorylation.
Step-by-step explanation:
Glycolysis Process Overview
Glycolysis is a metabolic pathway in which glucose is converted into pyruvate, with the net production of 2 ATP and 2 NADH. The process begins with the investment of 2 ATP molecules to activate glucose and ends with the production of 4 ATP molecules, resulting in a net gain of 2 ATP. This series of reactions occurs in the cytoplasm and does not require oxygen, making glycolysis an anaerobic process.
The first phase of glycolysis involves the consumption of ATP to phosphorylate glucose, which is subsequently cleaved into two three-carbon molecules. The second phase is responsible for producing ATP and reducing NAD+ to NADH. Finally, the three-carbon compounds are converted into pyruvate molecules. Throughout this process, 2 ATP are consumed at the start, but 4 ATP are produced by substrate-level phosphorylation, hence, there's a net gain of 2 ATP for the cell.
The NADH produced during glycolysis enters the mitochondria to participate in the oxidative phosphorylation process, which can generate a substantial amount of additional ATP. However, if a cell lacks sufficient oxygen, pyruvate is subjected to anaerobic pathways, such as fermentation, that do not yield additional ATP.