glykolysissä

Glycolysis, also known as the Embden-Meyerhof-Parnas pathway, is a fundamental metabolic process that occurs in the cytoplasm of nearly all living organisms. It is the initial stage of cellular respiration, where glucose, a six-carbon sugar, is broken down into two molecules of pyruvate, a three-carbon compound. This breakdown releases a small amount of energy in the form of ATP and also produces NADH, an electron carrier that will be used in later stages of cellular respiration to generate more ATP.

The glycolytic pathway consists of ten enzymatic reactions. The process can be divided into two main phases. The first phase, the energy investment phase, requires the input of two ATP molecules to convert glucose into two triose phosphate molecules. This phase involves the phosphorylation and rearrangement of glucose. The second phase, the energy payoff phase, involves the oxidation and phosphorylation of the triose phosphates, resulting in the production of four ATP molecules and two NADH molecules. Therefore, the net yield of glycolysis is two ATP molecules and two NADH molecules per molecule of glucose.

Glycolysis can occur in the presence or absence of oxygen. When oxygen is present, the pyruvate produced enters the mitochondria for further oxidation through the citric acid cycle and oxidative phosphorylation, leading to a much larger ATP yield. In the absence of oxygen, pyruvate undergoes fermentation, converting NADH back to NAD+ so that glycolysis can continue to produce ATP anaerobically. This anaerobic pathway is crucial for energy production in cells that lack mitochondria or during periods of high energy demand.