Post RN - Biochemistry (Unit 8) Metabolism of Carbohydrates

Metabolism of Carbohydrates

1. Biochemistry Lecture Post RN (Unit 8) Metabolism of Carbohydrates by, Miss Areesha Ahmad Lecturer

2. GLYCOGENESIS It is the process of storing excess glucose for use by the body at a later time in the form of glycogen . It is stored in the liver and muscle cells.

3. GLYCOGENOLYSIS The word lysis means break down. It is the process in which glycogen molecules breaks down into glucose molecules . The glycogen previously stored by the liver is broken down to glucose and dispersed throughout the body.

4. GLYCOLYSIS

5. GLUCONEOGENESIS Gluconeogenesis  (abbreviated  GNG ) is a metabolic pathway that results in the generation of glucose from non-carbohydrate carbon substrates such as pyruvate, lactate, glycerol . Glucose is the only energy source used by the brain . Gluconeogenesis  meets the needs of the body for glucose when sufficient carbohydrate is not available from the diet or glycogen reserves .

6. R ole of oxidative glucose catabolism in the citric acid cycle Oxidative glucose catabolism can be divided into three main stages : Glycolysis: The breakdown of glucose into pyruvate. Citric Acid Cycle: The oxidation of acetyl-CoA derived from pyruvate. Oxidative Phosphorylation: The production of ATP through the electron transport chain and chemiosmosis . Glycolysis Location: Cytoplasm Process: Glucose (6-carbon molecule) is broken down into two molecules of pyruvate (3-carbon molecules). Outcome: Produces 2 ATP molecules, 2 NADH molecules, and 2 pyruvate molecules.

7. Transition to the Citric Acid Cycle Before entering the citric acid cycle, pyruvate undergoes a transition step : Pyruvate Decarboxylation: Each pyruvate molecule is transported into the mitochondria, where it is converted into acetyl-CoA by the pyruvate dehydrogenase complex. This reaction produces one molecule of NADH and releases one molecule of CO2 per pyruvate . Pyruvate+CoA+NAD +→Acetyl-CoA+CO2​+ NADH Citric Acid Cycle (Krebs Cycle) Location: Mitochondrial matrix Primary Role: To oxidize acetyl-CoA to CO2 and capture high-energy electrons in the form of NADH and FADH2.

8. Steps of the Citric Acid Cycle Citrate Formation: Acetyl-CoA (2-carbon) combines with oxaloacetate (4-carbon) to form citrate (6-carbon). Acetyl-CoA+Oxaloacetate→Citrate 2. Isomerization to Isocitrate : Citrate is rearranged to form isocitrate . Citrate→ Isocitrate 3. Oxidative Decarboxylation to α- Ketoglutarate : Isocitrate is oxidized to α- ketoglutarate (5-carbon), producing NADH and releasing CO2 . Isocitrate+NAD + → α- Ketoglutarate+NADH+CO 2

9. 4. Oxidative Decarboxylation to Succinyl -CoA: α- Ketoglutarate is further oxidized to succinyl -CoA (4-carbon), producing another NADH and releasing CO2. α- Ketoglutarate+NAD ++CoA→Succinyl-CoA+NADH+CO2 ​ 5. Conversion to Succinate: Succinyl -CoA is converted to succinate, producing ATP (or GTP) in the process. Succinyl-CoA→Succinate+ATP ( orGTP ) 6. Oxidation to Fumarate : Succinate is oxidized to fumarate , producing FADH2. Succinate+FAD→Fumarate+FADH2 ​ 7. Hydration to Malate: Fumarate is hydrated to malate.Fumarate+H2O→MalateFumarate+H 2​ O→Malate Fumarate+H 2​ O→ Malate 8. Oxidation to Oxaloacetate: Malate is oxidized to oxaloacetate, producing NADH.Malate+NAD +→ Oxaloacetate+NADHMalate+NAD + → Oxaloacetate+NADH

10. Products of the Citric Acid Cycle (per Acetyl-CoA ): 2 CO2 molecules: Released as waste products. 3 NADH molecules: High-energy electron carriers used in the electron transport chain. 1 FADH2 molecule: Another electron carrier for the electron transport chain. 1 ATP (or GTP) molecule: Direct energy currency of the cell. Regeneration of Oxaloacetate: Allows the cycle to continue.

11. Role in Energy Production The NADH and FADH2 produced in the citric acid cycle carry high-energy electrons to the electron transport chain (ETC) located in the inner mitochondrial membrane. Here, the electrons pass through a series of protein complexes, ultimately leading to the production of ATP through oxidative phosphorylation.