Catabolism : The degradative processes concerned with the breakdown of complex molecules to simpler ones, with a release of energy. Those reactions that transforms fuels into cellular energy are called catabolic reactions.
Anabolism: Those reactions that require energy are called anabolic reactions. E.g. Synthesis of DNA, glucose etc. The useful forms of energy that are produced in catabolism are employed in anabolism to generate complex structures from simple ones, or energy-rich states from energy-poor ones.
ATP is chemical link between catabolism and anabolism. It is infact the energy currency of living cell.
The very purpose of catabolism is to trap the energy of the biomolecules in the form of ATP and to generate the substances (precursors) required for the synthesis of complex molecules.
Catabolism occurs in three stages:
Stage 1: Conversion of complex molecules into their building blocks:
- Polysaccharides are broken down to monosaccharides, lipids to free fatty acids and glycerol, proteins to amino acids.
Stage 2: Formation of simple intermediate :
- The building blocks produced are degraded to simple intermediates such as pyruvate and acetyl CoA.
- These intermediates are not readily identifiable as carbohydrates, lipids or proteins. A small quantity of energy (as ATP) is captured in this step.
Stage 3: Final oxidation of acetyl CoA :
- Acetyl CoA is completely oxidized to CO2, liberating NADH and FADH2 that finally get oxidized to release large quantity of energy (as ATP).
- Krebs cycle (or citric acid cycle) is the common metabolic pathway involved in the final oxidation of all energy-rich
- This pathway accepts the carbon compounds (pyruvate, succinate etc.) derived from carbohydrates, lipids or proteins.
For the synthesis of a large variety of complex molecules, the starting materials are relatively few. These include pyruvate, acetyl CoA and the intermediates of citric acid cycle. Besides the availability of precursors, the anabolic reactions are dependent on the supply of energy (as ATP ) and reducing equivalents (as NADPH +H+).
Anabolic pathways require energy input, generally in form of phosphoryl group transfer potential of ATP and reducing power of NADP, NADPH and FADH2.
Anabolic and catabolic pathways are not reversible and operate independently. As such, the metabolic pathways occur in specific cellular locations (mitochondria, microsomes etc.) and are controlled by different regulatory signals.
Download Link: Catabolism and Anabolism.pdf