METABOLISM

METABOLISM

Introduction

The network of enzyme-catalyzed pathways constitutes cellular metabolism. Metabolism, the sum total of all the chemical transformation that occurs in a cell or organism, occurs in a series of enzyme-catalyzed reaction that constitute metabolic pathways. In the sequence of steps (the pathways), a precursor is converted into a product through a series of metabolic intermediates (the metabolites). Metabolic pathways are sometimes linear and sometimes branched, yielding several useful and end products from a single precursor or converting several starting from a single precursor or converting several starting materials in a single product.

Anabolism and Catabolism

Metabolism involves two fundamental processes, anabolism (assimilation or building up process) and catabolism (disintegration or tearing down processes). Anabolism is the conversion of ingested substances into constituents of protoplasm, whereas catabolism is the breakdown of substances into simpler substances, the end product usually being excreted. In anabolism, small, simple precursors are built up into larger and more complex molecules, including proteins, lipids and polysaccharides. Anabolic reactions require the input of energy, generally in the forms of free energy of hydrolysis of ATP and the reducing power of NADH and NADPH. Catabolism is the degradative phase of metabolism, in which organic nutrient molecules are converted into simpler and smaller products. Catabolic pathways release free energy, some of which is conserved in the formation of ATP and reduced electron carriers (NAD and NADPH). Most organisms have the enzymatic equipment to carry out both the degradation and the synthesis of certain compounds (e.g., fatty acids). The simultaneous synthesis and degradation of fatty acids would be wasteful and prevented by separately regulating anabolic and catabolic reaction sequences: when occurs, the other is suppressed.

Difference between Anabolism and Catabolism
Anabolism	Catabolism
1. Any constructive metabolic process by which organisms convert substances into other components of the organism’s chemical architecture. 2. It requires energy. 3. Anabolic process include multistage photosynthesis, protein synthesis, nucleic acid and polysaccharide synthesis 4. Reaction in this case is of divergence type.	Any degradative process of metabolism by which large molecules are broken down into smaller ones It releases energy. The sum of enzymatic breakdown, such as digestion and respiration in an organism. Reaction in this case is of convergence type

Thermodynamics

Modern organisms carry out a remarkable variety of energy transduction, conversions of one form of energy to another. The energy conversions, which are vital for life, are regulated by “the two laws of thermodynamics”. The first law of thermodynamics is the principle of the conservation of energy- in any physical or chemical change, the total; amount of energy in the universe remains constant, although the form of energy may change. The second law of thermodynamics states that the universe always tends towards more and more disorder- in all natural process, the entropy of the universe increases. Living organisms consist of molecules much more highly organized than the surrounding materials from which they are made of, and they maintain and produce order, seemingly obvious to the second law of thermodynamics. Living organisms do not violate the second law of thermodynamics; they operate strictly within it. In short, living organisms preserve their internal order by taking from the surroundings free energy in the form of nutrients or sunlight, and returning to their surroundings and equal amount of energy as heat and entropy (the extent of randomness or disorder in a system).