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Enzymes

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Enzymes are complex macromolecules proteinaceous in composition,  colloidal and thermolabile in nature which are used  to increase the rate of chemical reaction in living organisms without itself being unchanged. In fact, enzymes are the biocatalysts (catalysts of living organisms).

The term enzyme isolated was from is extract and called as zymase that converted sugar into alcohol. This was shown by Buchner in 1897 for which he was awarded Nobel prize in 1903. Some nai 1926 show the protein nature of enzymes and was also awarded Nobel prize for proving that enzymes can be crystallized.

Types of Enzymes 

On the basis of functioning in or out of living cells enzymes are of two types:

  • Exoenzymes
  • Endoenzymes

Exoenzymes: Exoenzymes are the the extracellular enzymes released by the living cells and catalyse the biochemical reaction outside the living cells for example enzymes of digestive juices, lysozymes of tears.

Endoenzymes: Endoenzymes are the intracellular enzymes produced by the living cells and function inside the living cells. For example: enzymes of glycolysis and Kreb's cycle.

Similarly, on the basis of composition  enzymes can be categorised into two groups

  • Simple Enzymes
  • Conjugated Enzymes

Simple Enzymes : Simple enzymes are composed of proteins only without any additional group. For example trypsin, Urease, Pepsin etc.

Conjugated Enzymes: Conjugated enzymes are composed of proteins along with some non proteinaceous additional group for example carboxylase, transferases etc.

Except few enzymes like RNA enzymes all enzymes are made of protein which is found which is the functional unit or active part of enzyme called holoenzyme. It is generally composed of two types: 

  • Apoenzyme: It is the the proteinases part of enzyme.
  • Cofactors: It is the the non protein non proteinaceous part in the  which may or may not be separated from apoenzyme. Cofactors are either inorganic (For eg: metal ions and iron sulphur groups) or organic. Organic cofactors which are released from the active site of enzyme during the reaction  are co- enzymes and the cofactors which are tightly covalently bound to a enzymes are called prosthetic groups.

Active Site of Enzyme 


The part of enzyme which gets actively involved in binding with the substrate before undergoing catalysis is known as active site of enzyme. Similarly the another small part involved in catalytic process is called catalytic site . Both binding site and catalytic site it makes the active site of enzyme and enzyme have may have one to two several active sites each consisting of few amino acids.

During the the reaction an enzyme combines with the substrate at its active site and forms of substrate enzyme- complex. These complexes later break down into you want her more end products depending on the type of chemical reaction but the enzyme remains unchanged. Enzyme activity has been found to be influenced by bhai number of factors such as temperature, PH , water concentration of substrate and enzyme. Enzyme activity is easily lost by the denaturation or degradation of protein part of enzyme which occurs by a number of factors such as heat high energy radiation size of of heavy metals and organic solvents.

Function of Enzymes

  • Enzymes catalyse all kinds of chemical reaction in living cells that are involved during various biological activities such as growth, respiration, digestion and excretion.
  • Deficiency of particular enzyme may result to many heriditary diseases like albinism, phenylketonuria.
  • Many enzymes  such as amylase, protease break down larger molecules into smaller ones so that they can be easily absorbed by body of organisms.
  • Some enzymes act as a ion pumps of the cell for the movement of ions across the plasma membrane in active transport mechanism.
  • Some enzymes are used in cellular defence mechanism and clearing process.