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.

6. 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

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

8. Glycogen 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.

9.  Functions of Glycogen
1. Maintenance of blood glucose level
2. Muscle glycogen-
- Quick source of energy for metabolism
- Exhausted in less than one hour
3. Liver glycogen-
- Reservoir of glucose for other tissues
- When dietory glucose is not available
- Imp for neurons(which only use glucose as a fuel)
- Can 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.

10. Overview of Metabolism
Glycogen Synthesis Glycogen Breakdown

11. Glycogenesis
Synthesis of glycogen from glucose
1. Synthesis of UDP-glucose-

12. 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-

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

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

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

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

17. • 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.

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