Enzymes: Action and Factors affecting

Catalysts are the substances which play a significant role in the chemical reaction. Catalysis is the phenomenon by which the rate of a chemical reaction is altered/ enhanced without changing themselves. During a chemical reaction, a catalyst remains unchanged, both in terms of quantity and chemical properties. An enzyme is one such catalyst which is commonly known as the biological catalyst.  Enzymes present in the living organisms enhance the rate of reactions which take place within the body. The nature of enzyme action and factors affecting the enzyme activity are discussed below.


Action and Nature of Enzymes

Enzymes are the biocatalysts with high molecular weight proteinous compound. It enhances the reactions which occur in the body during various life processes.It helps the substrate by providing the surface for the reaction to occur. The enzyme comprises of hollow spaces occupying groups such as -SH, -COOH,  etc., on the outer surface. The substrate which has the opposite charge of the enzyme fits into these spaces just like key fits into a lock. This substrate binding site is called the active site of an enzyme (E).

Enzymes action

Once substrate (S) binds to this active site, they form a complex (intermediate-ES) which then produces the product (P) and the enzyme (E) The substrate which gets attached to the enzyme has a specific structure and that can only fit in a particular enzyme. Hence by providing a surface for the substrate, an enzyme slows down the activation energy of the reaction. The intermediate state where the substrate binds to the enzyme is called the transition state. By breaking and making the bonds, the substrate binds to the enzyme (remains unchanged), converts into the product and later splits into product and enzyme. The free enzymes then bind to other substrates and the catalytic cycle continues until the reaction completes.

The enzyme action basically happens in two steps:

Step1: Combining of enzyme and the reactant/substrate.

E+S → [ES]


Step 2: Disintegration of the complex molecule to give the product.


Thus, the whole catalyst action of enzymes is summarized as:

E + S → [ES] → [EP] → E + P

Nature of Enzymes action

Factors Affecting Enzyme Activity

The conditions of the reaction have a great impact on the activity of the enzymes. Enzymes are particular about the optimum conditions provided for the reactions such as temperature, pH, alteration in substrate concentration, etc.

Temperature and pH

Enzymes require an optimum temperature and pH for their action. The temperature or pH at which a compound shows its maximum activity is called optimum temperature or optimum pH respectively. As mentioned earlier, enzymes are the protein compounds. A temperature or pH more than optimum may alter the molecular structure of the enzymes. Generally, an optimum pH for enzymes is considered to be ranging between 5 and 7.

Factors Affecting Enzyme Activity

Concentration and Type of Substrate

Enzymes have a saturation point i.e., once all the enzymes added are occupied by the substrate molecules, its activity will be ceased.  When the reaction begins, the velocity of enzyme action keeps on increasing on further addition of substrate. However, at a saturation point where substrate molecules are more in number than the free enzyme, the velocity remains the same.

The type of substrate is another factor that affects the enzyme action. The chemicals that bind to the active site of the enzyme can inhibit the activity of the enzyme and such substrate is called an inhibitor. Competitive inhibitors are chemicals that compete with the specific substrate of the enzyme for the active site. They structurally resemble the specific substrate of the enzyme and bind to the enzyme and inhibit the enzymatic activity. This concept is used for treating bacterial infectious diseases.

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Practise This Question

The curve given below shows enzymatic activity with relation to three conditions (pH, temperature and substrate concentration). What do the two axes (x and y) represent?