Glycoliza

Glycoliza, also known as glycolysis in many contexts, is the cytosolic metabolic pathway that converts one molecule of glucose into two molecules of pyruvate. The process does not require oxygen and provides a rapid source of energy and metabolic intermediates for other pathways. It consists of ten enzyme-catalyzed reactions, organized into two phases: an investment phase that uses two ATP, and a payoff phase that yields ATP and NADH.

Key steps include the initial phosphorylation of glucose by hexokinase or glucokinase to form glucose-6-phosphate, isomerization to fructose-6-phosphate, and a critical phosphorylation by phosphofructokinase-1 (PFK-1) to fructose-1,6-bisphosphate. This intermediate is split by aldolase into dihydroxyacetone phosphate and glyceraldehyde-3-phosphate (G3P), with the DHAP isomerizing to another molecule of G3P. The G3P is oxidized by glyceraldehyde-3-phosphate dehydrogenase, producing NADH, followed by substrate-level phosphorylation steps mediated by phosphoglycerate kinase and pyruvate kinase that generate ATP. The final product is pyruvate.

Net yield per glucose molecule is two ATP (four produced minus two invested), two NADH, and two pyruvate. Under anaerobic conditions in many cells, pyruvate is reduced to lactate to regenerate NAD+, allowing glycolysis to continue. In aerobic conditions, pyruvate can enter mitochondria and be converted to acetyl-CoA for the citric acid cycle and oxidative phosphorylation, increasing total energy yield.

Glycolysis is tightly regulated, with PFK-1 acting as a major control point; its activity responds to cellular energy status via ATP, AMP, citrate, and fructose-2,6-bisphosphate levels. The pathway is conserved across organisms and serves as a central source of ATP and metabolic precursors.