·         Enzymes are catalysts which speed up the chemical reaction by providing an alternative reaction pathway of lower activation energy.

·         Like all catalysts, enzymes take part in the reaction but they do not undergo permanent changes and remain unchanged at the end of reaction.

·         Enzymes can only alter the rate of reaction but do not alter the position of equilibrium.

·         Enzymes are highly selective catalyzing specific reaction only. This specificity is due to the shape of enzyme molecule.

·         Enzymes are proteins that increase the rate of chemical reaction by lowering the activation energy of a reaction.

Properties of enzyme:

Ø  Enzymes work at optimal p H and temperature making them most environmentally friendly solution for industrial manufacturing.

Ø  Enzymes are biodegradable and keep on working until they are dissolved usually by other enzymes.

Ø  All enzymes are proteins but not all proteins are enzymes: Proteins are building blocks of all living organisms. Humans, plants, animals and micro-organisms are all made up of proteins. Proteins constitute 80% of dry weight of muscle, 70% of dry weight of skin and 90% of dry weight of blood.

Structure of enzymes:

Enzymes consists of a protein part called apoenzymes and non protein part called cofactor.  Apoenzyme and cofactor combine to form Holoenzyme. Proteins in enzymes are usually globular. Their folded confirmation creates an area called as active site. The nature and arrangement of amino acids in the active site make it specific for only one type of substrate. The intermolecular and intramolecular bonds that hold proteins in their secondary and tertiary structure are disrupted by change in temperature and Ph. This affects shapes and catalytic activity of the enzyme. So enzymes are temperature and Ph sensitive.

Enzymes are highly selective, they catalyze specific reaction only. Enzymes have a part of molecule, where it just has the shape where only certain kind of substrate can bind to it, this site of activity is known as active site. The molecule that reacts and binds to the enzyme is called as substrate.

Cofactors are generally categorized into following types:

1.       Prosthetic group

2.       Activators

3.       Coenzymes

1.       Prosthetic group: Prosthetic groups are organic group that are permanently bound to the enzymes.

·         Eg:   Heme group of cytochromes

·         Biotin group of acetyl co A carboxylase


2.       Activators: They are positively charged metal ions or cations which temporily bind to the active site of the enzyme and giving an intense positive charge to the enzyme’s protein.

Eg: Fe-cytochrome oxidase

      Ca- catalase

      Zn- alcohol dehydrogenase

       Mg- glucose 6 phosphate

3.       Coenzymes: Coenzymes are organic molecule which are not primarily bound to the enzyme molecule but combine with the enzyme- substrate ( E-S) complex temporily.

Eg: FAD ( Flavin Adenine Dinucleotide), FMN ( Flavin Monophosphate Nucleotide), NAD (Nicotinamide Adenine Dinucleotide)

Classification of Enzyme:

Enzymes are classified on the basis of reaction they catalyze into six types:

1)      Oxidoreductases: They catalyze oxidation – reduction reaction. Oxidoreductase are responsible for the production of heat and energy.

Eg: Alcohol dehydrogenase converts primary alcohol to aldehyde.

C2H5OH+ NAD         CH3CHO+NADH+H+

In this reaction ethanol is converted to acetaldehyde and the cofactor NAD is converted              to NADH. In other words ethanol is oxidized and NAD is reduced.

2)      Transferases: It is also known as group transfer reaction. Transferases catalyze those reactions where transfer of functional groups occur between two substrate.

Eg: Alanine aminotransferase shuffles the alpha amino group between alanine and aspartate.


3)      Hydrolases: They are also called as hydrolytic enzyme, they catalyze hydrolysis reaction of carbohydrates, proteins and esters.

Eg: Phosphatase breaks the oxygen-phosphate bond of phosphate esters


4)      Lyases: They catalyze reaction involving the removal of groups from substrate by processes other than hydrolysis by the formation of double bond .

Eg :Decarboxylases remove CO2 from alpha or beta  keto acids


5)      Isomerases: They catalyze the reaction where interconversion of cis and trans isomers is involved.

Eg: Triose phosphate isomerase carry out these rearrangements


6)      Ligases: They are called as synthases, these are the enzyme that catalyze the reaction where coupling of two compounds is involved with the breaking of pyrophosphate bonds.

Eg: Aminoacyl transfer RNA synthetase and join amino acid to their respective transfer RNA’s in preparation for protein synthesis ; the action of glycyl-t RNA synthetase is illustrated in this figure


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