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What Are Enzymes: Functions, Type, Definition & Characteristics

User Mark time03 May,2019

What is enzyme?

Enzymes are biological molecules (mainly proteins) produced by a living organism which act as catalysts in the body. It increases the rate of any chemical or biochemical reaction going on in any part of the body. The best part is that it takes part in allmost all biological reactions, but themselves does not undergo any change in structure themselves.

Enzymes: Functions

Enzymes takes place in almost all biological functions like Digestion and , MetabolismWaste secretion and others.

Lets dig a little deep into what enzymes does in the body. For sider that we need to consider how our body is formed.

Evcery cell in the body consists of water, inorganic ions and carbon containing organic molecules. These organic molecules of the cells during digestion , metabolism, waste secretion, undergoes reaction with other molecules.

Enzymes speed up the reactions occuring in these biomolecules or chemicals of the cells.

Lets consider A and B are the biomolecules reacting to give C.

And D is the enzyme

A+B—– (t time)——-C ( time required for the reaction and the product C to form, let it be t)

On action of enzyme D

A+B—- (>t) ——-C ( the time required for the product C to be formed is lesser than time ton action of enzyme).

The product C is the blue coloured shape.

The product A and B are purple coloured shape.

The Enzyme D is the green coloured shape.

Enzymes acts as a lock for both the molecules A and B.

During reaction , it forms a complex or a loosely bond single structure as shown in the second part of the diagram. After that, the two chemicals or biomolecules undergo change to form C a single product while the enzyme shown in green colour doesnt go under any structural change.

Enzymes also acts on single molecules in the following manner


A single molecule consisting of two parts ( elements like carbon , hydrogen or smaller molecular group like C00,OH (hydroxyl).

During enzymatic action, they fit into the grooves of the enzyme molecular structure (1,2,3). The enzyme aids the dissociation of the parts of molecules or compounds into separate components (4). In the process the enzyme remains intact but the compound or molecule changes into individual components.

Enzymes continue to perform the vital functions in a body as long as a “substrate” ( the chemicals or biomolecules on which enzyme acts)  is present. Enzymes can be composed of one or innumerable chains of intertwined amino acids.  The unique sequence of amino acids gives each of the enzymes its characteristic shape.

Note: All enzymes are proteins but all proteins , which do not have catalytic functions, are not enzymes

Phe-Leu-Ser-Cys is the chain of amino acids.

The sequence of this chain determines the charectersticks of the enzymes.

If the sequence changes like


Then the charectersticks of the enzyme changes alltogether.

Lock and key Model

On the surface, each enzyme has a special cleft called the “active site.” This provides the place where reagents meet and interact. It works like a lock and key system. The enzyme takes a specific shape that allows only a particular type of reagent to fit with it like a jigsaw puzzle. In each case, the enzyme retains its original state once the products leave the active site of the enzymes.

This model has been updated and is called the ‘induced fit model.

Allosteric Enzymes

However, the phenomenon is slightly different in case of allosteric enzymes. Allosteric enzymes contain a second type of site, called the allosteric site apart from the active site. Non-substrate molecules bind with the allosteric site, influencing the activity of the enzymes. They have multiple polypeptide chains with multiple allosteric and active sites that help them to respond to several different conditions in their environment.

—An inhibitor can lock itself into the enzyme allosteric site , changing the enzyme structure and hence disabling locking of the substrate and enzyme at the active site.

—The enzyme is made fit for locking the substrate by activators when they fit in the allosteric site

There are many types of inhibitors

Competitive inhibitors – a molecule fits in the active site and block the space. Here the the substrate has to compete with the inhibitor to attach to the enzyme. One which reaches faster or is more fit to get locked in the enzyme structure wins the race.

Non-competitive inhibitors – a molecule fits in to a cleft in the enzyme structure, different from the active site. It causes slight alteration in structure of the active site and reduces the catalytic efficiency of the enzyme on the locked substrate..

Uncompetitive inhibitors – This inhibitor binds to the enzyme and substrate locked in the enzyme structure The products  formed by the catalytic action of enzyme on substrate leaves the active site less easily, and hence the reaction is slowed down.

Irreversible inhibitors – an irreversible inhibitor binds to an enzyme and permanently changes the structure and its ability to lock in substrates and thereby inactivates the enzymes catalytic power.


Allosteric enzymes play a crucial role in cell signalling and regulation of metabolism.. Several activities take place inside a cell at any specific point of time to maintain a proper balance within the cell. The allosteric enzymes help to maintain the balance.

Characteristics of allosteric enzymes

They have binding sites for regulatory molecules that are separate from the active site.

  • They are small single subunit proteins
  • They have the ability to interconvert between a more active form and less active form.

What Is The Function Of An Enzyme?

Life would have ceased to exist without enzymes. Enzymes are found in a variety of cells and each performs a vast amount of complex tasks.

Here is a list of functions performed by certain enzymes in our body

  • Lipases – an enzyme group that help in digesting fats in the gut.
  • Amylase – Amylase is present in saliva.It helps in breaking down starch to simple sugars
  • Maltase – also found in saliva; breaks the sugar maltose into glucose. Maltose is found in foods such as potatoes, pasta, and beer.
  • Trypsin – found in the small intestine, breaks proteins in the food into amino acids ( the units of proteins) and thereby helps in digestion.
  • Lactase – It is found in small intestine, breaks lactose, the sugar into milk, into glucose and galactose.
  • Pancreatic enzymes: A group of enzymes that breaks down fats, carbohydrates and proteins
  • The fundamental function of an enzyme is to lower the activation energy of a reaction ( the energy required for the reaction to take place). In simpler terms, enzymes lower the amount of energy that is required for any reaction to begin and hence speed up the chemical reaction a million times faster, than it would have been without it. They bind to the reactant molecules and hold them in a specific way so that chemical bonding and any bond formation process take place more rapidly.
  • Some of the enzymes are responsible for creating a favourable environment inside the active site (when it is slightly acidic or nonpolar) that aids the reaction.
  • Certain types of enzymes lower the activation energy by taking part in some chemical reaction. In this case, the residues of active siteslower their energy to form temporary covalent bonds with substrate molecules. (However, we should remember that in each case the key factor is that the temporariness. They go back to their original state once the reaction is complete.)
  • A hallmark property of enzymes is that it is never altered in any way by the reactions it catalyses. Every enzyme returns to its original state once it releases the product at the end of the reaction. It is then ready for the next cycle of catalysis.

Why Do All Enzymatic Reactions Need Activation Energy? 

All kinds of biological processes need the energy to function properly.  For example, let’s imagine you need to climb up to the top of a hill to reach the other side. The higher the hill is, the more energy you will need to climb to the top of it.

Similarly, molecules require a certain amount of energy to start a chemical reaction. This energy is known as the activation energy.

A molecule is at a lower energy level. It will need more energy to get to the top of the reaction “hill”. This energy is provided by the activation energy. It helps the enzyme to attain the top most position of the reaction hill and ensures a successful chemical reaction.

 Some or all the chemical bonds of the reactants need to be broken to form new bonds for a reaction to take place. To get the bonds into a state that allows them to break, the molecules are deformed and bent into an unstable state known as the transition state. The activation energy aids the molecules to reach the transition state. This transition state is a higher energy state. The transition state of an enzyme is extremely unstable. The reactant molecules don’t stay there for long but quickly proceed to the next step of the chemical reaction once it reaches this stage.

Your school curriculum might assign you this question on enzymes

Some truths about the wonder proteins, called enzymes

  • It is a protein.
  • It is a catalyst.
  • It binds to specific substrates.
  • It is small compared to its substrates.

Properties Of Enzymes

Some of the most important properties of an enzyme are its proteinous/colloidal nature, substrate specificity, catalytic properties, turnover number and its sensitivity towards pH, temperature and inhibitors.

  • Nearly all enzymes are proteins in nature.
  • In the protoplasm, certain enzymes exist as hydrophilic colloids and can be isolated by dialysis.
  • Enzymes are specific to its substrate and each enzyme catalyses only one or similar type of reactions.
  • Every enzyme initiates the rate of catalysis by lowering the activation energy.
  • Each enzyme has a specific turnover number i.e. the number of substrate molecules changed per unit of time for one enzyme. It varies from 102 to  103sec-1.
  • Enzymes are extremely sensitive to changes in pH temperature and inhibitors. They operate within a narrow range of optimum conditions.

Biology is a broad discipline and comprises of various complicated chapters. Each chapter is further divided into subtopics that deal with the intricate functions of living organisms. Do have a dearth of understanding of the complex enzymatic reactions? Contact our experts to improve your basic concepts of biology.

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