Glicòlisi

Glicòlisi is a fundamental metabolic pathway that occurs in the cytoplasm of nearly all living cells. This process breaks down a single molecule of glucose, a six-carbon sugar, into two molecules of pyruvate, a three-carbon compound. Glycolysis is the initial stage of cellular respiration, whether under aerobic or anaerobic conditions. It is an ancient pathway, suggesting it evolved early in the history of life.

The entire process of glycolysis involves a series of ten enzyme-catalyzed reactions. It can be broadly divided into two phases: the energy investment phase and the energy payoff phase. In the energy investment phase, two molecules of ATP are consumed to activate the glucose molecule and prepare it for cleavage. Subsequently, in the energy payoff phase, four molecules of ATP are produced, resulting in a net gain of two ATP molecules per glucose molecule. Additionally, glycolysis produces two molecules of the electron carrier NADH.

The pyruvate produced at the end of glycolysis can then enter different pathways depending on the availability of oxygen. In aerobic conditions, pyruvate is further processed in the mitochondria through the citric acid cycle and oxidative phosphorylation to generate a large amount of ATP. In anaerobic conditions, pyruvate is converted into lactate or ethanol through fermentation, regenerating NAD+ which is essential for glycolysis to continue. This anaerobic ATP production, while less efficient than aerobic respiration, is vital for survival in oxygen-deprived environments.