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Mechanism of Enzymes Action

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  • Difficulty Level : Basic
  • Last Updated : 09 Oct, 2022
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Different types of cells, tissue, and other complex organs together form the human body. Our body releases some chemicals for the effective functioning of the body and to improve biological processes such as respiration, digestion, excretion, and a few other metabolic activities to maintain a healthy life. Hence, enzymes are essential for biological processes in all living organisms. 

Enzymes can be defined as biological polymers produced by living organism that catalyze the biochemical reactions. 

They are basically proteins that are produced by living organisms inside the body that help in facilitating certain metabolic and biochemical reactions. These are the biological catalysts that speed up the metabolic reaction inside the body. Enzymes are crucial for metabolic processes and other chemical reactions in the cell. They are necessary for sustaining the life of organisms. Enzymes are catalysts, so they do not involve directly in biological reactions but they help with their efficient occurrence. The metabolic processes depend on the enzymes which react with the molecule and are called the substrate. Enzymes convert the substrates into other distinct molecules known as products. Mostly they are found in all tissues and fluids of the body. The essential and critical life processes are exhibited based on the function of enzymes. The enzymes in the plasma membrane control the catalysis in the cells due to the response of cellular signals and enzymes in circulatory systems regulate the clotting of blood

Structure of Enzymes

Enzymes are mostly proteins. They have a primary structure i.e. linear chain of amino acids, which eventually form a three-dimensional shape. An enzyme like any protein has secondary and tertiary structures. In tertiary structure, the protein chains fold upon themselves, and the chain crisscrosses upon itself which creates many pockets or crevices. One such pocket is known as the ‘active site’ or the substrate-binding site. The substrate fits into a pocket or crevice which is the active site of an enzyme. Thus, the active site of an enzyme catalyzes the biochemical reactions at a high rate. The enzymes are able to break the bigger molecule into simpler molecules or vice versa. Enzymes get damaged at high temperatures (above 40oc) and high pressure, resulting in loss of enzyme activity. Thermal stability is thus an important factor of such enzymes. 

Enzymes are eventually larger with varying sizes, as compared to their substrate, ranging from 62 amino acid residues to 2500 residues found in fatty acid synthase. These amino acids are liked in a specific way to form different types of enzymes. Only a small part of the entire enzyme structure is used for catalysis and is situated next to binding sites. The enzyme’s active site consists of both the catalytic site and binding site together. The enzymes also have a site called the inhibitor site. This site is functional when the enzyme is in the inactivated state. The enzymes also have a model of lock and key structure. The active site of an enzyme is flexible and can be modified, and thus can be reshaped based on the interactions with corresponding substrates. 

What do enzymes do?

Enzymes are not living organisms and are a particular type of protein that helps in speeding up the biochemical reaction in our body. Each cell in the human body contains thousands of enzymes. Enzymes provide help with facilitating chemical reactions within each cell. As they are not destroyed during the process, a cell can reuse each enzyme repeatedly. The presence of these enzymes helps in many reactions inside the body that keep a person alive and well. They are important for digestion, oxidation, hydrolysis, respiration, muscle and nerve function, liver function, and much more. Enzymes in our blood assist with healthcare and check for injuries and diseases. Enzymes in our body catalyze all kinds of chemical reactions that include growth, blood clotting, diseases, breathing, etc. 

Mechanism of Enzyme 

These enzymes are low-blood protein bodies that are used to catalyze several chemical and biochemical reactions occurring in animal and plant bodies. Without enzymes, the living process will be too slow to sustain life. For example, in the absence of enzymes in our digestive tract, it would take us about 50 years to digest a single meal. Thus enzymes are necessary for life processes. 

  1. Enzymes have varying sizes of cavities.
  2. These cavities are present on the surface of colloidal particles of enzymes.
  3. These cavities are of a particular characteristic shape and they process active groups such as -NH2, -COOH, -SH, -OH, etc. 
  4. The cavities present on the surface of the enzyme are also the active site for biochemical reactions.
  5. The reactant molecule or substrate has a complementary shape to the active site or the cavity of the enzyme. They fit together like a key fit into a lock.
  6. An activated complex is formed on active groups (-NH2, -COOH, -SH, -OH, etc) these groups decompose to obtain final products. Thus, the enzyme-catalyzed reactions may be considered to proceed in two steps:
    • Binding reactant to the enzyme to form an activated complex (ES*).
    • Decomposition of the activated complex to form the product (P).

Enzyme Mechanism to Reduce Activation Energy

Activation energy is needed to break down chemical bonds allowing the reaction to occur. The activation energy describes how quickly a reaction takes place to be spontaneous. Enzymes reduce the activation energy of the reaction by lowering the bond energy of the bond that cannot be broken. By making the bond that cannot be broken higher in energy, it becomes easier to break the bond. When an enzyme binds to a substrate, it lowers the substrate molecules’ energy to react to form products. Enzymes reduce the size of the reactants and the size of the product, thus lowering the activation energy. 

They are also used for reducing the activation energy of a reaction in the real world in medicine, food manufacturing, and other industrial processes. They are also used in a wide range of technical processes. Enzymes are very versatile and efficient in nature which results in their application in different fields, they lower the activation energy, but also increase the possibility of the reaction. If the reaction were to happen spontaneously, an enzyme’s role is to lower the activation energy needed to start a reaction to proceed fastly without a temperature change. 

Functions of Enzymes

  • The enzyme kinase is commonly used in signal transducing in human bodies. This enzyme catalyzes the phosphorylation of proteins. the enzyme breaks down the large complex molecules into a simpler substances so that the body can absorb them easily. 
  • Enzymes are used in the synthesis of energy in our body, ATP synthase is the enzyme commonly used in this process. They carry out the transfer of ions across the plasma membrane. 
  • Enzymes perform a number of functions and reactions like oxidation, reduction, and hydrolysis. They are essential for digestion liver function and other bodily functions. 
  • Enzymes catalyze all the reactions involved in growth, blood coagulation, healing, breathing, reproduction, etc. They reorganize internal cellular structures for better cellular activities.

Lock and Key fit Hypothesis

For any reaction to occur there should be interaction or collision among the two molecules in the right direction and sufficient energy. The energy between the molecules should be more than the barrier in the reaction. This energy is called activation energy. Enzymes are said to be the active site which is a part of the molecule with a definite shape and the functional group for the binding of reactant molecules. When a molecule binds to the enzyme it is termed a substrate molecule. The enzyme and substrate together form the intermediate reaction with low activation energy without any catalysts. Enzymes help to reduce the activation energy of the molecules in the reaction. The enzyme-substrate reaction can be better explained with the lock and key structure mechanism. The enzyme is represented by the lock whereas the substrate represents the key. Each substrate belongs to a particular enzyme. 

Lock & Key Hypothesis

Lock and Key fit Model

The enzyme-substrate reaction can be expressed with this common equation. i.e. Substrate + Enzyme = (Substrate – Enzyme) > (Product – Enzyme or the intermediate) = Product + Enzyme. The main function of enzyme action is to catalyze chemical reactions. The binding of the substrate with the active site of the enzyme results in enzyme reactions, the active site is a specific area that combines with the substrate. 

Induced fit Hypothesis

The substrate gets attached to the enzyme which has a specific structure that can only be fitted in a particular enzyme. In Induced fit, the active site is not exactly complementary to the substrate but changes shape in the presence of a specific substrate to become complementary and initiate the reaction. When a substrate molecule interacts with an enzyme, if its composition is specifically correct, the shape of the enzyme’s Active site will change so that the substrate fits into it and an Enzyme – Substrate complex can be formed. After the reaction, an Enzyme-Product Complex is formed. The enzyme slows down the activation energy of the reaction by providing a surface to the substrate. The intermediate state where the substrate binds with the enzyme is called the transition state. The enzyme and substrate form bonds and then breaks them, which results in a product and later they split into product and enzyme. The enzymes then bind to other substrates the cycle continues till the reaction is completed. When the substrate (S) binds to its active site with the enzyme (E), a complex (intermediate ES) is developed which produces the product (P) and the enzyme. 

The steps included in enzyme actions are:

  • Step 1: The enzyme and substrate combine and result in an intermediate substrate.
  • Step 2: The detachment of complex molecules gives the product and enzyme. 

The entire catalyst reaction of enzymes can be expressed as:

E  +  S  —>  (ES)  —>   E  +  P

Induced Fir Hypothesis

Induced-fit Model

FAQs on Mechanism of Enzymes

Question 1: Explain the enzyme Ribozymes.


Ribozymes are basically molecules of ribonucleic acid, which catalyze the biochemical reaction in one of their own bonds or among other RNAs. They belong to the class RNA catalyst.

Question 2: How do enzymes work?


For any reaction to occur energy is required. Enzymes act as catalysts and help reduce the activation energy of the complex molecules and carry forward the reaction. The following steps simplify the working of the enzyme. 

  • Step 1: Each molecule has an active site where one of the substrate molecules can bind to and form an enzyme-substrate complex is formed. 
  • Step 2: This enzyme-substrate molecule form an end product from the substrate and the enzyme is liberated to react with another substrate molecule. 

Question 3: Describe the important properties of enzymes.


  1. Enzymes act as biological catalysts and speed up the rate of reaction.
  2. They convert one form of energy into a more useful form of energy required for the reaction. 
  3. Cofactors are the molecules that help the enzymes to carry forward the reaction. 
  4. Enzymes are highly specific, a particular enzyme binds to a particular substrate and catalyzes a single reaction. 
  5. They are mostly chains of amino acids or proteins, but some RNA molecules (ribozymes) can also act as catalysts.  

Question 4: State the uses of enzymes. 


  • Alcoholic Beverages are prepared by different enzyme actions. The use of various enzymes on different plant products creates a variety of fermented product
  •  Daily consumable food products are created with the help of enzymes. The finest example of fermentation is Bread. It occupies its texture due to the use of enzymes during the fermentation process. 
  • Enzyme action can be promoted by the use of drugs that tend to work around the active sites of enzymes.

Question 5: How enzyme works?


Enzyme accelerates the time of the reaction and changes the substrate into the product. The working of enzymes is explained by 2 hypothesis:

  • Lock and Key Hypothesis
  • Induced Fit Hypothesis

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