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Indeed, the reactions that make up glycolysis and its parallel pathway, the pentose phosphate pathway, can occur in the oxygen-free conditions of the Archean oceans, also in the absence of enzymes, catalyzed by metal ions, meaning this is a plausible prebiotic pathway for abiogenesis.
Aerobic glycolysis Glycolysis – The first stage is known as glycolysis, which produces 2 ATP molecules, 2 reduced molecules of nicotinamide adenine dinucleotide and 2 pyruvate molecules that move on to the next stage – the Krebs cycle. Glycolysis takes place in the cytoplasm of normal body cells, or the sarcoplasm of muscle cells.
An example of a coupled reaction is the phosphorylation of fructose-6-phosphate to form the intermediate fructose-1,6-bisphosphate by the enzyme phosphofructokinase accompanied by the hydrolysis of ATP in the pathway of glycolysis. The resulting chemical reaction within the metabolic pathway is highly thermodynamically favorable and, as a ...
The location where glycolysis, aerobic or anaerobic, occurs is in the cytosol of the cell. In glycolysis, a six-carbon glucose molecule is split into two three-carbon molecules called pyruvate. These carbon molecules are oxidized into NADH and ATP. For the glucose molecule to oxidize into pyruvate, an input of ATP molecules is required.
In the glycolytic pathway, 1,3-bisphosphoglycerate is dephosphorylated to form 3-phosphoglyceric acid in a coupled reaction producing two ATP via substrate-level phosphorylation. [5] The single phosphate group left on the 3-PGA molecule then moves from an end carbon to a central carbon, producing 2-phosphoglycerate.
The first reaction is the oxidation of glyceraldehyde 3-phosphate (G3P) at the position-1 (in the diagram it is shown as the 4th carbon from glycolysis), in which an aldehyde is converted into a carboxylic acid (ΔG°'=-50 kJ/mol (−12kcal/mol)) and NAD+ is simultaneously reduced endergonically to NADH.
Anaerobic glycolysis is thought to have been the primary means of energy production in earlier organisms before oxygen was at high concentration in the atmosphere and thus would represent a more ancient form of energy production in cells. In mammals, lactate can be transformed by the liver back into glucose using the Cori cycle.
The NAD+/NADH coenzyme couple act as an electron reservoir for metabolic redox reactions, carrying electrons from one reaction to another. [5] Most of these metabolism reactions occur in the mitochondria. To regenerate NAD+ for further use, NADH pools in the cytosol must be reoxidized.