enzymes notes

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1. Introduction to Enzymes:

Thousands of chemical reactions proceed very rapidly at any given instant within all living cells of an organism. Virtually all of these reactions are mediated by remarkable molecular devices called enzymes. That is, the enzymes are central to every biochemical reaction and are called the catalysts of biological systems (biocatalysts).

They in organized sequences and catalyse the hundreds of stepwise reactions by which nutrient molecules are degraded, chemical energy is conserved and transformed, and biological macromolecules are made from simple precursors. Through the action of regulatory enzymes, metabolic pathways are highly coordinated to yield a harmonious interplay among the many different activities necessary to sustain life.

Enzymes catalyse an enormous diversity of biochemical reactions due to their capacity to specifically bind a very wide range of molecules. By utilizing the full repertoire of intermolecular forces, enzymes bring substrates together in an optimal orientation, the prelude to making and breaking chemical bonds.

They catalyse reactions by stabilizing transition states, the highest energy-species in reaction pathways. By selectively stabilizing a transition state, an enzyme determines which one of several potential biochemical reactions actually takes place.

Until 1980s, all enzymes were believed to be proteins. Then, Tom Cech and Sidney Altman independently discovered that certain RNA molecules may function as enzymes may be effective biocatalysts. These RNA biocatalysts have come to be known as ribozymes.

 Meaning of Enzyme:

An enzyme is a protein that is synthesised in a living cell and catalyses or speeds up a thermodynamically possible reaction so that the rate of the reaction is compatible with the biochemical process essential for the maintenance of the cell. It is sometimes called as organic catalyst or biocatalyst.

Over 90% of enzymes are simple globu­lar proteins (Fig. 8.14). The remainder is conjugated proteins, which have a non­-protein fraction called the prosthetic group. Many enzymes have relative molecular mass of between 10,000 and 50,000da.

 Biological Importance of Enzymes:

(i) Thousands of chemical reactions are taking place in the body of a living organism. All of them are mediated by enzymes,

(ii) Enzymes are specialised catalysts that operate at biological temperatures,

(iii) Enzyme mediated reactions do not require harsh treatment,

(iv) They are pH specific so that reactions requiring different pH operate in different parts of the body,

(v) As they operate under favourable conditions, enzymes force the organisms to live under favourable environment,

(vi) Enzymes are highly regulated. Their formation is controlled by separate genes. Activation and repression of genes allow certain enzymes to be functional or non-functional in cells.