Glycolysisbas

Glycolysis is a central metabolic pathway that occurs in nearly all living organisms, serving as the primary method for converting glucose into energy. The term originates from the Greek words *glykys* (sweet) and *lysis* (splitting), reflecting its role in breaking down glucose. This process takes place in the cytoplasm of cells and is divided into two main phases: the energy investment phase and the energy payoff phase.

The pathway begins with glucose, which is phosphorylated by ATP to form glucose-6-phosphate, preventing its exit from the cell. Through a series of enzymatic reactions, glucose-6-phosphate is isomerized into fructose-6-phosphate and further phosphorylated to fructose-1,6-bisphosphate. This molecule is then cleaved into two three-carbon sugars, glyceraldehyde-3-phosphate (G3P) and dihydroxyacetone phosphate, which interconvert to maintain an equal distribution.

In the energy payoff phase, G3P undergoes oxidation and phosphorylation, producing NADH and 1,3-bisphosphoglycerate. This compound is then dephosphorylated to generate ATP, yielding a net gain of two ATP molecules per glucose molecule. The remaining intermediates are rearranged and dehydrated, forming pyruvate, which can enter the citric acid cycle or be converted into lactate under anaerobic conditions.

Glycolysis is regulated by enzymes such as hexokinase, phosphofructokinase-1 (PFK-1), and pyruvate kinase, which respond to cellular energy levels, substrate availability, and feedback inhibition. This pathway is crucial for energy production, biosynthetic processes, and maintaining cellular homeostasis, particularly in rapidly dividing cells and tissues with high energy demands.