<h2>Carbohydrate Metabolism - Glycolysis</h2>

Students should know the most common pathways that occur in metabolism of carbohydrates. The pathways include the following

• Glycolysis  - breakdown of glucose 
• Pyruvate metabolism
• Glycogenesis  - synthesis of glycogen
• Glycogenolysis - breakdown of glycogen
• Pentose phosphate pathway
• Metabolism of fructose
• Metabolism of galactose
• Gluconeogenesis - synthesis of glucose from non-carbohydrate sources
• Cori cycle

Glycolysis

• Glycolysis is the breakdown of glucose to produce energy and occurs in all living cells
• Site of glycolysis in the cell - cytoplasm (important to remember this)
• Glycolysis can occur in the presence of oxygen (aerobic) or in the absence of oxygen (anaerobic) but the end products are different
• Products of aerobic glycolysis - Two pyruvate + 2 ATP + 2 NADH following glycolysis of 1 glucose molecule
• Product of anaerobic glycolysis - 2 ATP + 2 lactate from glycolysis of 1 glucose molecule

The lactate thus formed is utilized to regenerate NAD+ to keep glycolysis going (in the absence of NAD+ glycolysis cannot occur).

Applied Concepts:

• Deficiency of any of the enzymes (most commonly pyruvate kinase) in the glycolytic pathway can lead to hemolysis of RBC as red cells depend on glucose for their energy and will breakdown if their energy requirements are not met
• Skeletal muscle is adapted for anaerobic glycolysis and ATP is provided in the absence of oxygen
• Blood glucose values in a test tube can be lower than actual values of the patient since anaerobic glycolysis can still occur within the test tube with formation of lactate. This can be prevented by adding fluoride which inhibits glycolysis to the test tube 
• Effect of arsenate on glycolysis - prevents ATP formation by uncoupling the GAPDH and PGK reactions. Interestingly it does not inhibit any of the enzymes involved