What is Glycolysis?
Glycolysis is a fundamental
biochemical pathway that occurs in the cytoplasm of cells. It involves the breakdown of one molecule of glucose into two molecules of pyruvate, generating a small yield of
ATP and
NADH in the process. This pathway is crucial for cellular metabolism and energy production, particularly in the absence of oxygen.
Energy Production: It provides a quick source of ATP, which is essential for various cellular activities.
Anaerobic Conditions: It can occur without oxygen, making it vital for cells in anaerobic conditions.
Metabolic Intermediates: It generates intermediates used in other metabolic pathways such as the
citric acid cycle and
pentose phosphate pathway.
Hexokinase: Phosphorylates glucose to glucose-6-phosphate.
Phosphoglucose Isomerase: Converts glucose-6-phosphate to fructose-6-phosphate.
Phosphofructokinase-1: Phosphorylates fructose-6-phosphate to fructose-1,6-bisphosphate.
Aldolase: Cleaves fructose-1,6-bisphosphate into glyceraldehyde-3-phosphate and dihydroxyacetone phosphate.
Triose Phosphate Isomerase: Converts dihydroxyacetone phosphate to glyceraldehyde-3-phosphate.
Payoff Phase
Glyceraldehyde-3-Phosphate Dehydrogenase: Converts glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate, producing NADH.
Phosphoglycerate Kinase: Converts 1,3-bisphosphoglycerate to 3-phosphoglycerate, generating ATP.
Phosphoglycerate Mutase: Converts 3-phosphoglycerate to 2-phosphoglycerate.
Enolase: Converts 2-phosphoglycerate to phosphoenolpyruvate.
Pyruvate Kinase: Converts phosphoenolpyruvate to pyruvate, generating ATP.
Hexokinase: Inhibited by its product, glucose-6-phosphate.
Phosphofructokinase-1 (PFK-1): The main regulatory enzyme, allosterically inhibited by ATP and activated by AMP and fructose-2,6-bisphosphate.
Pyruvate Kinase: Inhibited by ATP and alanine, activated by fructose-1,6-bisphosphate.
Pyruvate: Can enter the
mitochondria for further oxidation in the citric acid cycle or be converted to lactate in anaerobic conditions.
ATP: A net gain of 2 ATP molecules per glucose molecule.
NADH: Two molecules of NADH per glucose, which can be used in the electron transport chain to produce more ATP.
Aerobic Respiration: In the presence of oxygen, pyruvate enters the mitochondria and is converted to acetyl-CoA, which enters the citric acid cycle.
Anaerobic Respiration: In the absence of oxygen, pyruvate is converted to lactate in animals (lactic acid fermentation) or ethanol and CO2 in yeast (alcoholic fermentation).
Citric Acid Cycle: Pyruvate enters this cycle for further ATP production.
Gluconeogenesis: Some intermediates of glycolysis can be used to synthesize glucose.
Pentose Phosphate Pathway: Provides NADPH and ribose-5-phosphate for anabolic reactions.
