JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Pharmacy II BIOCHEMISTRY Previous Question Paper (August/September - 2022 - R17)

The Citric Acid Cycle (Krebs cycle) is the final common oxidative pathway for carbohydrates, fats, and amino acids. It occurs in the mitochondrial matrix.

1. Acetyl-CoA (2C) condenses with Oxaloacetate (4C) to form Citrate (6C) via citrate synthase.
2. Citrate is isomerized to Isocitrate by aconitase.
3. Isocitrate undergoes oxidative decarboxylation to α-Ketoglutarate (5C) by isocitrate dehydrogenase, releasing CO2 and NADH.
4. α-Ketoglutarate is converted to Succinyl-CoA (4C) by the α-ketoglutarate dehydrogenase complex, releasing CO2 and NADH.
5. Succinyl-CoA is converted to Succinate by succinyl-CoA synthetase, generating GTP (or ATP).
6. Succinate is oxidized to Fumarate by succinate dehydrogenase, producing FADH2.
7. Fumarate is hydrated to Malate by fumarase.
8. Malate is oxidized to Oxaloacetate by malate dehydrogenase, producing NADH.

Energetics per one Acetyl-CoA molecule: 3 NADH (7.5 ATP), 1 FADH2 (1.5 ATP), and 1 GTP/ATP. The total yield per turn is 10 ATP.

Gluconeogenesis is the synthesis of glucose from non-carbohydrate precursors like lactate, glycerol, and glucogenic amino acids, primarily occurring in the liver and kidneys.

1. Pyruvate to Oxaloacetate via pyruvate carboxylase (requires ATP).
2. Oxaloacetate to Phosphoenolpyruvate (PEP) via PEP carboxykinase (requires GTP).
3. The pathway proceeds through the reversal of glycolysis steps until Fructose-1,6-bisphosphate.
4. Fructose-1,6-bisphosphate is converted to Fructose-6-phosphate by fructose-1,6-bisphosphatase.
5. Fructose-6-phosphate isomerizes to Glucose-6-phosphate.
6. Glucose-6-phosphate is converted to free Glucose by glucose-6-phosphatase.

Significance: It maintains blood glucose levels during fasting, starvation, or intense exercise, ensuring a continuous supply of glucose for the brain and erythrocytes, which are obligate glucose users.