Glycolysis is the sequence of reactions that converts glucose into pyruvate with the concomitant production of a relatively small amount of adenosine triphosphate (ATP). The word is derived from Greek
(sweet) and
?? (letting loose).
It is the initial process of most carbohydrate catabolism, and it serves three principal functions:
1. Generation of high-energy molecules (ATP and NADH) as cellular energy sources as part of aerobic respiration and anaerobic respiration; that is, in the former process, oxygen is present, and, in the latter, oxygen is not present.
2. Production of pyruvat for the citric acid cycle as part of aerobic respiration.
3. Production of a variety of six- and three-carbon intermediate compounds, which may be removed at various steps in the process for other cellular purposes.
As the foundation of both aerobic and anaerobic respiration, glycolysis is the archetype of universal metabolic processes known and occurring (with variations) in many types of cells in nearly all organisms. Glycolysis, through anaerobic respiration, is the main energy source in many prokaryotes, eukaryotic cells devoid of mitochondria (e.g., mature erythrocytes) and eukaryotic cells under low-oxygen conditions (e.g., heavily-exercising muscle or fermenting yeast).
Glycolysis takes place in the cytosol. In plant cells, some of the glycolytic reactions are also found in the Calvin-Benson cycle, which functions inside the chloroplasts. The wide conservation includes the most phylogenetically deep-rooted extant organisms, and thus it is considered to be one of the most ancient metabolic pathways.
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