Glykolys

Glykolys, often called glycolysis in English, is a central metabolic pathway that converts a six-carbon glucose molecule into two molecules of pyruvate. During the process, cells harvest energy by producing ATP and reducing equivalents in the form of NADH. Glykolys occurs in the cytosol of nearly all organisms and functions under both aerobic and anaerobic conditions, providing energy quickly and supplying chemical intermediates for other pathways.

It consists of ten sequential enzymatic reactions organized into two phases: an energy investment phase that consumes two ATP, and an energy payoff phase that ultimately yields four ATP and two NADH per glucose, giving a net gain of two ATP. Key steps are driven by enzymes such as hexokinase, phosphofructokinase-1, aldolase, glyceraldehyde-3-phosphate dehydrogenase, and pyruvate kinase, which channel glucose to pyruvate through glyceraldehyde-3-phosphate and related intermediates.

Under aerobic conditions, pyruvate is transported into mitochondria and converted to acetyl-CoA by the pyruvate dehydrogenase complex, feeding the citric acid cycle and oxidative phosphorylation. In the absence of oxygen, pyruvate is reduced to lactate in many animals or decarboxylated to ethanol and CO2 in yeast and some bacteria, allowing glycolysis to continue by regenerating NAD+.

Regulation of glycolysis is tightly controlled to match cellular energy needs. Phosphofructokinase-1 (PFK-1) is a major rate-limiting control point, responding to energy status via ATP, AMP, citrate, and fructose-2,6-bisphosphate. Other steps, including those catalyzed by hexokinase and pyruvate kinase, provide additional regulation, coordinating glycolysis with other pathways.

Glykolys is foundational to metabolism, supplying rapid ATP, providing carbon skeletons for biosynthesis, and linking to the mitochondria or fermentation pathways depending on conditions. It is among the oldest and most conserved metabolic pathways and remains a focus of research in bioenergetics, cancer metabolism, and metabolic diseases.