Enzyme Its Structure And Mechanism

   ENZYMES:

Enzymes are biological catalyst mean they can speed up biochemical reaction. All enzymes are Protein except RIBOZYME which consist of RNA and found in ribosomes. Enzymes mainly work in both VIVO and VITRO. Without enzymes there is no concept of life. Enzymes are not required in large amount small amount of enzymes can convert huge amount of substrate into product

STRUCTURE:

The function of enzyme is to speed up the reaction and this catalytic activity of enzyme is located in its active site which is a charge bearing three dimensionall cavity. The substrate can attach to active site by hydrophobic interactions or hydrogen bonding. Active site contain 3-12 amino acids which are scattered in polypeptide and brought into a particular fasion in secondary and tertiary folding of proteins molecule.

Active site consist of two functional region
1-Binding site
2- Catalytic site
Amino acids of active site that make bond with substrate constitute the binding site and some amino acids which convert the substrate into product constitute the catalytic site.
Some enzymes also need a non protein part which is called COFACTOR which is not only responsible for the attachment of substrate with acive site but also take part in catalytic process. The final shape of active site establish after the attachment of cofactor. Enzymes that need cofactor become active only if cofactor is attach to it such an active enzyme is called HOLOENZYME. If cofactor is not attach to enzyme then enzyme is inactive mean it is not able to attach substrate with it such an inactive enzyme is called APOENZYME.
Some other enzymes which donot need cofactor also show active or inactive state for example: pepsin is an enzyme which is released by the gastric glands of stomach in inactive form Pepsinogen. In this inactive form it has additional polypeptide fragment which is attached to active site and not allow the active site to bind with substrate. When pepsinogen exposed to HCL in the stomach the additional polypeptide fragment remove from due to which pepsinogen convert into its active form which is pepsin

COFACTOR:

Cofactor are
1-Activator
2-Coenzyme
3-Prosthetic Group
Activators are inorganic cofactor. It include metallic ions such as FE2+,MG2+etc. They are detachable cofactor
Coenzymes are organic cofactor. They are detachable cofactor. They are derivatives of vitamins such as ATP,NAD+,FAD+etc

Prosthetic group are covalently bonded part of enzymes mean they are not detachable cofactor. They are organic cofactor. An iron containing porphyrin ring attach to enzyme cytochrome is the example of prosthetic group

MECHANISM:

when enzyme catalyze a reaction first thing that happen is substrate attach with enzyme to form ENZYME-SUBSTRATE COMPLEX. Then enzyme change substate into product while product don't remove from enzyme. It attach to enzyme(EP COMPLEX). Then the product  remove from enzyme making it capable to start a reaction again.

LOCK AND KEY MODEL:

EMIL FISCHER proposed this model in (1894). According to this model active site of enzyme has definite shape and rigid structure. Mean after or before the reaction the shape of active site doesnot change it remain same. Due to this specifity a particular substat attach to active site no other substrate can attach to active site. We also say that enzyme can perform only one type of reaction. This model is followed by very few number of enzymes. The enzyme which work according to this model are known as NON-REGULATORY ENZYMES. When one enzymes can perform only one type of reaction and no other then this is known as ABSOLUTE SPECIFITY.

INDUCE FIT MODEL:

Koshland can give the induced fit model. According to this model acive site shape is not rigid mean active site is flexible and it change it's shape as substrate interact with it. The change which is induced in the active site is responsible for the conversion of substrate into product and this flexiblity made possible for enzyme to catalyze more then one type of reaction. The enzyme which follow Induced fit model are known as REGULATORY OR ALLOSTERIC ENZYMES.
Example is carbonic anhydrase which add oxygen to  haemoglobin  and also catalyze the formation of carbonic acid and bicarbonates