Carbohydrate metabolism

carbohydrate metabolism, glycogen metabolism, glycolysis, glycogenolysis,etc.

1. CARBOHYDRATE METABOLISM M.Sc. I Roll No. 12

2. Hexose Monophosphate Pathway (HMP) Also called as HMP shunt or Pentose Phosphate Pathway (PPP) or Phosphogluconate pathway . Alternative route for metabolism of glucose. Significance - Biosynthesis of NADPH and Pentose sugar . NO ATP is consumed or produced. Location - In cytoplasm of liver and adipose tissue , etc. It helps in- 1. Formation of NADPH for synthesis of F.A. and steroids . 2. Prevent cell from oxidative damage. 3. Synthesis of Ribose for nucleotide and nucleic acid formation .

3. Steps of Pentose Phosphate Pathway Oxidative Phase This phase is Irreversible . Glucose-6-phospshate Ribulose-5-phosphate + 2 NADPH Non-oxidative Phase This phase is Reversible . it catalyze the conversion of pentose produced in phase one into 2 molecules of Glyceraldehyde-3-phosphate and Fructose-6-phoshate.

4. Gamma Amino Butyrate Shunt Converts glutamate to succinate via γ - Amino Butyric acid ( GABA) GABA has an amino group on the γ -carbon rather than on the α -carbon. Glutamate is Decarboxylated to give GABA Catalyzed by pyridoxal phosphate dependant Glutamate Decarboxylase . GABA undergoes transamination followed by oxidation to form succinate which enters TCA cycle

5. Function of GABA An inhibitory neurotransmitter – in brain. Regulates activity of neuron.

6. Glyco gen Metabolism Glycogen is the storage form of glucose in animals Excess glucose is converted into glycogen for storage. It is stored in cytosol of liver and muscle cells in the form of granules. Glycogen Granules- complex aggregates of glycogen + enzymes for synthesis and degradation + machinery for regulating these enzymes.

7. Functions of Glycogen 1 . Maintenance of blood glucose level 2 . Muscle glycogen- - Quick source of energy for metabolism - E xhausted in less than one hour 3 . Liver glycogen- - R eservoir of glucose for other tissues - W hen dietory glucose is not available - I mp for neurons(which only use glucose as a fuel ) - C an be deployed in 12-24 hours . Why To Store Glycogen as a Fuel Reserve? 1 . Rapidly mobilized 2 . Can generate energy in absence of oxygen 3 . Brain depends on continuous supply of glucose- mostly comes from glycogen.

8. Overview of Metabolism Glycogen Synthesis Glycogen Breakdown

9. Glycogenesis Synthesis of glycogen from glucose Synthesis of UDP-glucose-

10. 2. Requirements of Primer To Initiate Glycogenesis- * Small fragment of preexisting glycogen- Primer * Primer absent - glycogen initiator synthase- glycogenin accept glucose from UDP-glucose. 3. Glycogen Synthesis By Glycogen Synthase-

11. 4. Formation Of Branches In Glycogen Net reaction- (Glucose) n + Glucose + 2 ATP (Glucose) n+1 + 2 ADP + Pi

12. Glycogenolysis Degradation of stored glycogen Action Of Glycogen Phosphorylase degrade α - 1,4- Glycosidic bond Phosphorylosis - Limit Dextrin

13. 2. Action Of De-branching Enzyme- Transferase activity - α – 1,4 glycosidic bond Glucosidase activity- α - 1,6 glycosidic bond

14. 3. Formation of glucose-6-phosphate to glucose- Reaction catalyzed by phosphoglucomutase

15. The catalytic site of glucose 6-phosphatase faces the lumen of the ER. A glucose 6-phosphate (G6P) transporter (T1 ) carries the substrate from the cytosol to the lumen, and the products glucose and Pi pass to the cytosol on specific transporters (T2 and T3 ). Glucose leaves the cell via the GLUT2 transporter in the plasma membrane.

16. References Harper’s Biochemistry- 27 th Edition Principle Of Biochemistry -Lehninger Biochemistry – U. Satyanarayana .