Introduction to metabolism b.pharm

it will be helpful to various medical course students

1. Central Theme of Metabolism Metabolic fuels (carbohydrates, lipids and proteins) are broken down to as well as build up from smaller units such as glucose, fatty acids and amino acids by several metabolic pathways. The central theme of metabolism is to extract energy from food, store the excess for future needs and to maintain tissue proteins for performing various vital functions. The body uses glucose and fatty acids as the primary fuels to obtain energy. Only under dire circumstances, amino acids are used for this purpose. Glucose can be obtained from other carbohydrates, glucogenic amino acids and the ‘glycerol’ portion of fat. To synthesize tissue proteins, amino acids are required. Although glucose can be channelized to make some non-essential amino acids, fats cannot serve this purpose. When energy consumed is in surplus, the body converts all the three major nutrients into stored fat.

2. - Metabolism - The entire spectrum of chemical reactions, occuring in the living system, are collectively referred to as metabolism. - Metabolic pathway - A metabolic pathway (or metabolic map) constitutes a series of enzymatic reactions to produce specific products. - Metabolite - The term metabolite is applied to a substrate or an intermediate or a product in the metabolic reactions.

3. - Division of metabolism - Divided into two categories Catabolism The degradative processes concerned with the breakdown of complex molecules to simpler ones, with a concomitant release of energy. 2. Anabolism The biosynthetic reactions involving the formation of complex molecules from simple precursors. - Amphibolism - The term amphibolism is used for reactions which are both catabolic and anabolic in nature.

4. - Catabolism – - Purpose of catabolism - To trap the energy of the biomolecules in the form of ATP. To generate the substances (precursors) required for the synthesis of complex molecules. - Stages of catabolism – Three stages: Conversion of complex molecules into their building blocks. Formation of simple intermediates Final oxidation of acetyl CoA

5. - Anabolism - For the synthesis of complex molecules, the starting materials are relatively few. E.g. pyruvate, acetyl CoA and the intermediates of citric acid cycle. The anabolic reactions are dependent on the supply of energy (as ATP or GTP) and reducing equivalents (as NADPH + H + ). The anabolic and catabolic pathways are not reversible and operate independently. The metabolic pathways occur in specific cellular locations (mitochondria, microsomes etc.) and are controlled by different regulatory signals. - Intermediary metabolism - Intermediary metabolism refers to the entire range of catabolic and anabolic reactions, not involving nucleic acids.

6. - Types of metabolic reactions - The biochemical reactions are mainly of four types 1. Oxidation-reduction 2. Group transfer 3. Rearrangement and isomerisation 4. Make and break of carbon-carbon bonds