Catabolism - Glycolysis

ATP Production in Glycolysis

• A total of 4 ATP molecules are generated during the payoff phase of glycolysis.
• The net ATP production per glucose molecule in glycolysis is 2 ATP, considering 2 ATP are used in the preparatory phase.
• Glycolysis generates 2 NADH molecules per glucose molecule.

Irreversible Reactions in Glycolysis

• The irreversible reactions in glycolysis are catalyzed by hexokinase, phosphofructokinase (PFK), and pyruvate kinase.

ATP Requirements in Glycolysis

• The preparatory phase of glycolysis requires 2 ATP molecules for phosphorylation of glucose and fructose 6-phosphate.

Role of Mg2+ in Glycolysis

• The Mg2+ cofactor in Reaction 1 stabilizes the negative charges on ATP, facilitating its hydrolysis to ADP and inorganic phosphate.

Reaction Direction in Glycolysis

• Reaction 2 can proceed in the forward direction despite a positive ΔG° due to the low concentration of products, utilizing Le Chatelier's principle.

Rate-Limiting Step of Glycolysis

• The rate-limiting and committing step of glycolysis is catalyzed by phosphofructokinase (PFK), which converts fructose 6-phosphate to fructose 1,6-bisphosphate.

Effect of Triose Phosphate Isomerase Absence

• Without the function of triose phosphate isomerase, the conversion of dihydroxyacetone phosphate to glyceraldehyde 3-phosphate would be impaired, disrupting glycolysis.

Key Enzymes in Glycolysis

• The enzyme responsible for Reaction 6 is glyceraldehyde 3-phosphate dehydrogenase (GAPDH).
• Reaction 8 is catalyzed by phosphoglycerate mutase, with a ΔG° of approximately 0.
• Enolase is responsible for Reaction 9, converting 2-phosphoglycerate to phosphoenolpyruvate.
• The last step of glycolysis is catalyzed by pyruvate kinase.
• The enzyme responsible for forming fructose 1,6-bisphosphate is phosphofructokinase (PFK).
• The main rate-limiting reaction in glycolysis is also catalyzed by PFK.

Additional Enzymatic Actions and Requirements

• Aldolase catalyzes the formation of glyceraldehyde 3-phosphate and dihydroxyacetone phosphate.
• The conversion of glucose-6-phosphate (G-6-P) to fructose-6-phosphate (F-6-P) is catalyzed by phosphoglucose isomerase.
• Phosphoglycerate kinase catalyzes the conversion of 1,3-bisphosphoglycerate to 3-phosphoglycerate, producing ATP.
• Enolase produces phosphoenolpyruvate (PEP) from 2-phosphoglycerate.
• Pyruvate kinase produces pyruvate from phosphoenolpyruvate.
• Enzymes such as hexokinase, phosphofructokinase, and pyruvate kinase require magnesium as a cofactor.
• Phosphofructokinase (PFK) phosphorylates fructose 6-phosphate to fructose 1,6-bisphosphate.
• Triose phosphate isomerase catalyzes the interconversion of dihydroxyacetone phosphate and glyceraldehyde 3-phosphate.