Carbohydrate Metabolism

Carbohydrate Metabolism

General Introduction to Metabolism:

1) Anabolism: Building up phase, process of synthesizing complex compounds requires input or energy.

2) Catabolism: Process of decomposition of breakdown or complex substances like lipids, carbohydrates, proteins for release of energy. ATP storage form of energy.

Carbohydrate Metabolism:

Glycogenesis – transformation of sugar to glycogen
Glycogenolysis – Enzymatic breakdown of glycogen to glucose
Glyconeogenesis – Synthesis of glucose from non-carbohydrate material

Major Pathways of Glucose Utilization in cells of Higher Plants:
1) Glucose may be stored as polysaccharides or sucrose
2) Oxidized to 3 carbon compound (pyruate) via-glycolysis.
3) Oxidized to pentose via pentose phosphate pathway.

Three major inter related pathways of carbohydrate metabolism.

I) Glycolysis or EMP Pathway: Anaerobic conversion of glucose to pyruvic acid. Sequence of reaction that can operate without oxygen. Conversion of glucose to pyruvic acid and then to either ethyl alcohol or lactic acid

Explain Sequence of Reaction of Glycolysis:
Reversible reactions except conversion of fructose 1-6 diphosphate to fructose 6- phosphate yield 8 mole of ATP, 1 mole of glucose gives 2 moles of pyruvic acid.
II) Kreb’s cycle or TCA cycle or Citric Acid Cycle or Aerobic Oxidation of Pyruvic Acid:

Oxygen requiring continuation of glycolytic pathway under anaerobic condition pyruvic acid is converted into lactic acid but under aerobic conditions. Pyruvic acid is oxidized to CO2 and H2O through TCA cycle. Acetyl coenzyme A is the link between EMP pathway and Kreb’s Cycle common channel for product of glycolysis, ultimate oxidation of fatty acids and carbon skeleton of many amino acids.

Explain Sequence of Reactions in TCA Cycle:
Total energy output from glucose – One mole of glucose gives 38 moles of ATP (8 ATP from anaerobic glycolysis + 30 moles from TCA cycle).

III) Pentose phosphate pathway or phosphor gluconate pathway or Hexose monophosphate shunt or Warburg-Dicken’s pathway.

Major Function of  Warburg-Dicken’s Pathway:

1) It acts as a source of pentoses for nucleotides synthesis i.e. ultimately for nucleic acid synthesis.
2) It is considered the alternate route for metabolism of glucose.

Explain Sequence of Reactions of Pentose Phosphate Pathway:

3 phospho-glyceraldehyde and fructose 6- phosphate the end product of this pathway enters EMP pathway. Phospho-gluconate is a key intermediate produced during the reactions.

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