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Glycolysis is the metabolic pathway that converts glucose (C 6 H 12 O 6) into pyruvate and, in most organisms, occurs in the liquid part of cells (the cytosol). The free energy released in this process is used to form the high-energy molecules adenosine triphosphate (ATP) and reduced nicotinamide adenine dinucleotide (NADH). [1]
Glycolysis results in the breakdown of glucose, but several reactions in the glycolysis pathway are reversible and participate in the re-synthesis of glucose (gluconeogenesis). [9] Glycolysis was the first metabolic pathway discovered: As glucose enters a cell, it is immediately phosphorylated by ATP to glucose 6-phosphate in the irreversible ...
In the liver, muscles, and the kidney, this process occurs to provide glucose when necessary. [12] A single glucose molecule is cleaved from a branch of glycogen, and is transformed into glucose-1-phosphate during this process. [1] This molecule can then be converted to glucose-6-phosphate, an intermediate in the glycolysis pathway. [1]
"The metabolic pathway of glycolysis converts glucose to pyruvate via a series of intermediate metabolites. Each chemical modification (red box) is performed by a different enzyme. Steps 1 and 3 consume ATP (blue) and steps 7 and 10 produce ATP (yellow). Since steps 6-10 occur twice per glucose molecule, this leads to a net production of energy."
Though slower than glucose, its yield is much higher. One molecule of glucose produces through aerobic glycolysis a net of 30-32 ATP; [11] whereas a fatty acid can produce through beta oxidation a net of approximately 100 ATP depending on the type of fatty acid. For example, palmitic acid can produce a net of 106 ATP.
The ATP generated in this process is made by substrate-level phosphorylation, which does not require oxygen. Fermentation is less efficient at using the energy from glucose: only 2 ATP are produced per glucose, compared to the 38 ATP per glucose nominally produced by aerobic respiration. Glycolytic ATP, however, is produced more quickly.
Phosphorylation of glucose is a key reaction in sugar metabolism. The chemical equation for the conversion of D-glucose to D-glucose-6-phosphate in the first step of glycolysis is given by: D-glucose + ATP → D-glucose 6-phosphate + ADP ΔG° = −16.7 kJ/mol (° indicates measurement at standard condition)
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.