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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]
Aerobic respiration requires oxygen (O 2) in order to create ATP.Although carbohydrates, fats and proteins are consumed as reactants, aerobic respiration is the preferred method of pyruvate production in glycolysis, and requires pyruvate to the mitochondria in order to be oxidized by the citric acid cycle.
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.
The second substrate-level phosphorylation occurs by dephosphorylating phosphoenolpyruvate, catalyzed by pyruvate kinase, producing pyruvate and ATP. During the preparatory phase, each 6-carbon glucose molecule is broken into two 3-carbon molecules. Thus, in glycolysis dephosphorylation results in the production of 4 ATP.
Glycolysis is viewed as consisting of two phases with five steps each. In phase 1, "the preparatory phase", glucose is converted to 2 d-glyceraldehyde-3-phosphate (g3p). One ATP is invested in Step 1, and another ATP is invested in Step 3. Steps 1 and 3 of glycolysis are referred to as "Priming Steps".
The anaerobic glycolysis (lactic acid) system is dominant from about 10–30 seconds during a maximal effort. It produces 2 ATP molecules per glucose molecule, [3] or about 5% of glucose's energy potential (38 ATP molecules). [4] [5] The speed at which ATP is produced is about 100 times that of oxidative phosphorylation. [1]
The production of ATP is achieved through the oxidation of glucose molecules. In oxidation, the electrons are stripped from a glucose molecule to reduce NAD+ and FAD. NAD+ and FAD possess a high energy potential to drive the production of ATP in the electron transport chain. ATP production occurs in the mitochondria of the cell.
In some tissues and organisms, glycolysis is the sole method of energy production. [2] This pathway is common to both anaerobic and aerobic respiration. [1] Glycolysis consists of ten steps, split into two phases. [2] During the first phase, it requires the breakdown of two ATP molecules. [1]