Basics Of Pharmacy: Enzymes Classification And Functions

Monday, November 8, 2021

Enzymes Classification And Functions

Enzymes are biological polymers that act as a catalyst in the human body to perform many life important functions.

For easy understanding enzymes are defined as,

Enzymes are proteins that are involved in increasing the process of metabolism or speed up chemical reactions in the human body.

Enzymes are organic compounds that have both constructive and destructive effects.

Enzymes are involved in building many substances and are also involved in the breakdown of different substances.

Structure Of Enzyme

Enzymes are made of proteins arranged in a specific way.

Active Site

The part of enzymes that bind with other structures is known as the active site.The active site has a unique and specific shape.


The substance where enzymes work or bind is known as substrate.


The result produced by acting enzymes on substrates is known as a product.


Cofactors are non-protein substances that are linked with enzymes and are important for the proper functioning of enzymes.

Without a cofactor, the enzyme is known as an apoenzyme.

Types Of Cofactor

There are three types of cofactors,

  • Prosthetic Group

  • Coenzyme

  • Metal Ions

Prosthetic Group

  • These are cofactors which are strongly attached to the enzyme.

  • Are attached all the time.


  • Coenzyme only binds with enzymes during catalysis.

Metal Ions

  • For some enzymes, the metal ion is essential at the active site for performing catalytic activity.

  • Zn²+ is a metal ion cofactor.

Working Of Enzymes

Enzymes are very specific in performing their functions.

The working of enzymes was explained by the lock and key model by Emil Fischer in 1894 and the lock and key model is based on the concept of lock and key. 

As a specific key is used to open the specific lock in the same manner according to the lock and key model a specific active site binds with the substrate to convert it into the product.

In 1958 Daniel Koshland proposed another theory known as the Induced fit model.

According to the induced-fit model

enzymes have flexibility in their shapes and the shape of the active site continues to change until it completely binds the substrate.

Enzymes act as catalysts meaning enzymes start the reaction and convert substrate into products and reattach and can be used again and again.

Enzymes Nomenclature

As we know that enzymes are specific in their functions and a specific enzyme reacts with substrate to initiate catalytic reaction so the word "ase" is added at the end of the substrate name. For example, the word urease is used for the enzyme involved in the breakdown of urea.

Classification Of Enzymes

Enzymes are classified into 6 types of classes which are given as follow,

  • Isomerases

  • Hydrolases

  • Oxidoreductase

  • Lyases

  • Transferases

  • Ligases


  • Isomerases is the class of enzymes that are involved in catalysing the reactions which are involved in the structural rearrangements of molecules.


  • Alanine Racemase


  • These are the enzymes that are involved in breaking the bonds using water molecules.


  • Esterases


  • This class of enzyme is involved in catalysing the electron transfer from an electron donor to an electron acceptor.


  • It is the class of enzymes that are involved in the breakdown of bounds using mechanisms other than hydrolysis and oxidation.


  • Citrate lyase


  • It is the class of enzymes that helps in the transfer of functional groups between acceptor and donor.


  • Transaminase


  • It is the class of enzymes that is involved in the ligation process catalysis.


  • DNA ligase

Functions Of Enzymes

Enzymes are very important for performing different functions in the body and some main functions of enzymes are given as below,

  • Enzymes are involved in the breakdown of large molecules into small molecules and the process is called catabolism.

  • Many enzymes take part in construction activities and the process is called anabolism.

  • Enzymes are involved in the process of providing energy to the body i.e from ATP.

  • Enzymes also work as ion pumps in cell membranes.

  • Enzymes are involved in oxidation, reduction reactions in the body.

  • Enzymes are involved in hydrolysis reactions in the body.

  • Enzymes play an important role in the process of digestion.

  • Enzymes play an important role in the process of respiration.

Factors Affecting Enzymes Activity

The enzyme activity is affected by different factors which are given as below,

  • Concentration Of Enzyme

  • Concentration Of Substrate

  • Effect Of Temperature

Concentration Of Enzyme

  • The enzyme activity is directly related to the concentration of enzymes. The speed of enzyme activity is increased as the concentration of enzymes is increased.

Concentration Of Substrate

  • The rate of enzyme reaction is increased with an increase in substrate concentration but this increase is limited to a certain range of substrate concentration.

  • When all the active sites of enzymes are covered by substrate the enzymes are known as in saturated condition.

Effect Of Temperature

  • Temperature also has a direct impact on enzyme activity.

  • When we increase the temperature the activity of the enzymes is also increased but it is observed that this increase continues up to a specific maximum temperature and then continues to decline.

  • The optimum temperature at which most of the enzymes give maximum activity is 40-45 °C and at high temperature, activity is lost due to disarrangement of protein molecules in enzyme structure.

  • Some enzymes remain active even at 100°C.

Inhibitors Of Enzyme Activity

Some molecules attach with enzymes and prevent the enzymes from performing their normal working.

There are the following types of enzyme inhibitors,

  • Competitive Inhibitors

  • Noncompetitive Inhibitors

  • UnCompetitive Inhibitors

Competitive Inhibitors

  • Competitive inhibitors are those molecules that have the same structure or shape as substrate.

  • These false shaped substrate molecules compete with original substrate molecules for active site attachment.

  • If these inhibitors attach with active sites then these prevent the formation of enzyme-substrate complex.

  • It is reversible and also known as temporary binding.

Non Competitive Inhibitors

  • Non-competitive enzyme inhibitors are the molecules that attach to enzymes at sites other than active sites.

  • The site at which non-competitive inhibitors attach is known as the allosteric site.

  • When these molecules attach to the allosteric sites it results in a change in the structure of the enzyme and the enzyme-substrate complex is not formed.

UnCompetitive Inhibitors

  • Uncompetitive enzyme inhibitors are not able to bind with substrate or active site rather these attach to the enzyme-substrate complex.

  • This type of binding is permanent and known as irreversible binding.

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