What is the first step of glycolysis?

The first step of glycolysis involves the phosphorylation of glucose, which is the primary reaction that initiates the glycolytic pathway. In this step, a phosphate group is transferred from ATP (adenosine triphosphate) to glucose, converting it into glucose-6-phosphate. This reaction is catalyzed by the enzyme hexokinase (or glucokinase in the liver), and it serves several essential purposes: it traps glucose within the cell, as the phosphorylated form cannot easily cross the cell membrane; it also prepares the glucose molecule for further breakdown into pyruvate for energy production.

This phosphorylation is crucial because it is an investment phase of glycolysis, requiring the consumption of ATP to facilitate further metabolic processes. The subsequent reactions in glycolysis will utilize the glucose-6-phosphate to produce energy in the form of ATP and NADH, making this initial step vital to the entire metabolic pathway. Phosphorylation is thus regarded as the first critical step in glycolysis, laying the groundwork for the conversion of glucose into energy-rich molecules.