Classifications of Enzymes – Characteristics and Structure of Enzymes

What are Enzymes? Enzymes are very important group of bio molecules synthesized by living cells. They act as a catalyst. Enzymes accelerate the rate of reaction. Classified in to 6 groups.

What does enzyme do?

  • Enzyme increases the rate of reaction
  • It does not participate in reaction it just accelerate reaction

Where enzymes are made?

Enzymes are called bio catalyst because it is synthesized by living cell. Enzymes are protein in nature and produced on free ribsomes and ribosomes are attache on endoplasmic reticulum in cytoplasam. After production on ribosomes they undergo post-translation modification which proceed an other organelle  called golgi bodies.

Characteristics of Enzymes

Enzyme acts as a catalyst

Enzyme act on a substance convert it in to product. Many biological processes occurred in living organism and act as a catalyst in biological processes.

Enzyme has catalytic activity to accelerate the reaction in biological process by reducing activation energy. It could be used again and again in one type of reaction.

For one reaction only one type of enzyme could be used it is lock key model. For example like for one lock only one key is required same as one enzyme is used for one reaction. Enzyme is specific in its nature.

A reaction acquired minimum amount of energy to convert in to product before a chemical reaction which is called energy of activation. Activation energy can be decrease by increase the temperature.

What is activation energy?

Energy which is required to convert reactant in to product is called activation energy.

Enzymes are Protein

Enzymes are composed or made by protein. All the enzymes are protein in nature and having large mol wt. And Proteins made by Amino acids.

Specifically Functions

Enzyme can not function for many substrates. “One Enzyme One Substrate” is widely used term. One substrate is catalyzed by one enzyme only.

Reverse Function

Its function only to accelerate rate of reaction and it goes on until reaction reached equilibrium stage. it does not determine the direction of reaction.

Small Amount Requirement

Enzymes are able to catalyze chemical reactions from very small amount.

What is co-enzyme?

Some enzyme is simple protein and some are conjugated and non-protein part of such enzymes is called prosthetic group and also co-enzyme.


Coenzyme is organic non-protein molecule which is bind to protein part. This non-protein part is heat stable as well as having low molecular wt. co-enzyme can bind with apoenzyme with covalently or non-covalently

What is Apoenzyme and Holoenzyme?

Protein part of enzyme is called apoenzyme and protein and non-protein part collectively called holo enzyme.

How Enzymes are named?

Enzymes are generally named after adding the suffix “ase” to the name of

Enzyme involved in oxidation reduction reaction is called oxidoreductase and involved as a classification of Enzyme.

What is Zymogen?

Zymogen is those enzymes which are found in active form. Some time it could be active by auto catalyst

Sometime active form of catalyst acts on zymogen and converted its inactive form in to active.

Classification of Enzyme


The enzyme which is involved in oxidation and reduction reaction of its substratr is called oxidoreductase e.g xanthine oxidase, lactate dehydrogenase gG-6-P dehydrogenase etc.


Transferase is responsible to transfer one functional group from one molecule to another molecule like hexokinase, phosphor-glocomutase etc.


Class of Enzyme which involve in hydrolysis, e.g pepsin glucose 6 phosphatase and glycoside hydrolases.


This class of Enzyme is involved removal of small molecule from large substrate, Fumarase, histadine decarboxylase etc.


This Enzyme responsible for isomerization of substrate, e.g . UDP- glucose, epimerase, retinal isomerase,etc


One more class of Enzyme is called Ligase. This is involved joining of two substrate whit each other, e,g , glutamine synthase, RNA synthase

Structure of Enzymes

Lock and key model

This model first porposed by fischer. He represented that active site of enzyme is found in proper confirmation. Active site of enzyme provide fix and rigid shape in which substrate can fixed. It provides the same shape like substrate.

Substrate fits into active site of enzyme like key and lock model. As key can fix in a proper lock similarly a substrate can fix in proper enzyme which has same shape of substrate. Enzymes are specific in its nature. It means that one substrate for one enzyme. No one other substrate could fix in one type of enzyme as one lock has one key similarly one enzyme has one substrate.

Leave a Comment