Glycolysis

• Glycolysis key information:

  • Glycolysis is the process of oxidizing glucose, a six-carbon molecule, to eventually convert it into pyruvate, two three-carbon molecules
  • Glucose is a monosaccharide, a type of sugar, obtained from the diet and brought into cells for oxidation
• Glucose is a water-soluble solute and requires specialized transporters called GLUT transporters to move through the cell membrane

  • GLUT transporters are bidirectional, allowing glucose to move in and out of cells
  • Different types of GLUT transporters include GLUT1 for red blood cells, GLUT2 for the liver and kidneys, GLUT3 for neurons, and GLUT4 for muscle and adipose tissue
• Glucose is converted to glucose 6-phosphate by enzymes hexokinase or glucokinase, depending on the tissue

  • This conversion involves adding a phosphate group from ATP to the sixth carbon of glucose
• Glucose 6-phosphate is isomerized to fructose 6-phosphate by the enzyme phosphohexose isomerase
• Fructose 6-phosphate is converted to fructose 1,6-bisphosphate by the enzyme phosphofructokinase-1 (PFK-1), which involves the addition of another phosphate group from ATP
• Fructose 1,6-bisphosphate is cleaved into dihydroxyacetone phosphate (DHAP) and glyceraldehyde 3-phosphate (GA3P) by the enzyme aldolase

  • DHAP is converted to GA3P by the enzyme triose phosphate isomerase
• GA3P is further converted to 1,3-bisphosphoglycerate by a series of reactions involving the transfer of phosphate groups and the generation of ATP
• Overall, glycolysis involves a series of enzymatic reactions that convert glucose into pyruvate, generating ATP and NADH in the process
• 1,3-bisphosphoglycerate is a molecule with two phosphates, one on the first carbon and one on the third carbon
• The enzyme involved in the conversion of 1,3-bisphosphoglycerate is glyceraldehyde 3-phosphate dehydrogenase
• Glyceraldehyde 3-phosphate dehydrogenase adds NAD+ to glycerol 3-phosphate, removing hydrides from the GA 3 P and converting it into NADH
• In the process, two NADH molecules are produced
• An inorganic phosphate is added by GA 3 P dehydrogenase, generating NADH
• 1. phosphoglycerate is a molecule with a phosphate on the third carbon
• Phosphoglycerate kinase converts 3-phosphoglycerate into ATP, producing two ATP molecules
• 1. phosphoglycerate is a molecule with a phosphate on the second carbon
• Phosphoglycerate mutase converts 3-phosphoglycerate into 2-phosphoglycerate
• Phosphoenolpyruvate is a molecule with a phosphate on the second carbon
• Enolase converts 2-phosphoglycerate into phosphoenolpyruvate
• Pyruvate kinase converts phosphoenolpyruvate into pyruvate, producing two ATP molecules
• Under anaerobic conditions, pyruvate can be converted into lactic acid by lactate dehydrogenase
• Lactate dehydrogenase is a reversible enzyme that converts pyruvate into lactic acid
• High levels of lactate dehydrogenase in the blood can indicate conditions like myocardial infarction or metabolic acidosis
• Glycolysis occurs in the cytoplasm of the cell
• The starting substrate of glycolysis is glucose
• The end product of glycolysis is two pyruvate molecules
• Glycolysis generates a net of two ATP molecules and two NADH molecules
• Glycolysis is usually an anaerobic process, producing lactic acid in the absence of oxygen