Enzyme Catalysis

Enzyme catalysis is an important topic covered under the chapter of “Surface Chemistry” in NCERT Chemistry books for Class 12. Enzymes are complex nitrogenous substances (proteins) that have high relative molar mass with order of 10,000 or even more and are derived from living organisms. Specific reactions may be catalysed with the involvement of microorganisms in bulk like yeast or by the process of chemical synthesis and then performing the process of extraction from them like yeast extract. Most of the biochemical procedures, such as digestion and biosynthesis, are catalysed by enzymes.

Students require proper guidance to improve their scores in board examinations. The syllabus for NCERT class 12th is quite similar to that of different entrance examinations. Students need to cover all the topics to be fully prepared for entrance examinations like JEE, BITSAT and other state level examinations. Embibe offers solution sets for NCERT books that can be followed by the students to understand the correct approach to answer the questions. Students can further refer to previous year question papers and download the PDF of NCERT books to enhance their preparations for both boards and entrance examinations.

Enzyme Catalysis: Overview

Several chemical and biochemical reactions occurring in the animal and plant bodies are catalysed by an essential group of low blood proteins called enzymes. 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 essential for the life process.

Enzymes may be defined as an essential class of globular proteins that act as biocatalysts in the living systems and are produced by the living cells.

Chemically all enzymes are globular proteins. However, some enzymes are associated with some non-protein components called the prosthetic group. The prosthetic groups could be either metal ions such as \({\rm{Z}}{{\rm{n}}^{{\rm{ + 2}}}}{\rm{,M}}{{\rm{g}}^{{\rm{ + 2}}}}{\rm{,M}}{{\rm{n}}^{{\rm{ + 2}}}}{\rm{,C}}{{\rm{o}}^{{\rm{ + 2}}}}{\rm{,}}{{\rm{K}}^{\rm{ + }}}{\rm{,N}}{{\rm{a}}^{\rm{ + }}}\) or small organic molecules. When the prosthetic group is a metal Ion, it is called a cofactor. In case the prosthetic group is a small organic molecule, it is referred to as a co-enzyme. Many of the co-enzymes for the biological process are derived from vitamins like thiamine, riboflavin, and niacin.

In such enzymes, the protein part of the enzyme is called the apoenzyme. Neither apoenzyme nor co-enzyme can catalyse the reaction alone. The two must combine before acting as a catalyst. Since the action of an enzyme, in particular, every biological reaction requires a specific type of enzyme. To date, more than \(3000\) different kinds of enzymes have been identified in living systems, each catalysing a different biological reaction.

Enzyme Catalysis Examples

Examples of enzyme catalysis is listed as follows:

1. Inversion of cane sugar: The enzyme invertase converts cane sugar to glucose and fructose.

\({{\rm{C}}_{{\rm{12}}}}{{\rm{H}}_{{\rm{22}}}}{{\rm{O}}_{{\rm{11}}}}\left( {{\rm{aq}}} \right){\rm{ + }}{{\rm{H}}_{\rm{2}}}{\rm{O}}\left( {\rm{l}} \right) \to {{\rm{C}}_{\rm{6}}}{{\rm{H}}_{{\rm{12}}}}{{\rm{O}}_{\rm{6}}}\left( {{\rm{aq}}} \right){\rm{ + }}{{\rm{C}}_{\rm{6}}}{{\rm{H}}_{{\rm{12}}}}{{\rm{O}}_{\rm{6}}}\left( {{\rm{aq}}} \right)\)

2. Conversion of glucose into ethyl alcohol: The enzyme zymase converts glucose into ethyl alcohol and carbon dioxide.

\({{\rm{C}}_{\rm{6}}}{{\rm{H}}_{{\rm{12}}}}{{\rm{O}}_{\rm{6}}}\left( {{\rm{aq}}} \right) \to {\rm{2}}{{\rm{C}}_{\rm{2}}}{{\rm{H}}_{\rm{5}}}{\rm{OH}}\left( {{\rm{aq}}} \right){\rm{ + 2C}}{{\rm{O}}_{\rm{2}}}\left( {\rm{g}} \right)\)

3. Conversion of starch into maltose: The enzyme amylase converts starch into maltose.

\({\rm{2}}{\left( {{{\rm{C}}_{\rm{6}}}{{\rm{H}}_{{\rm{10}}}}{{\rm{O}}_{\rm{5}}}} \right)_{\rm{n}}}\left( {{\rm{aq}}} \right){\rm{ + n}}{{\rm{H}}_{\rm{2}}}{\rm{O}}\left( {\rm{l}} \right) \to {\rm{n}}{{\rm{C}}_{{\rm{12}}}}{{\rm{H}}_{{\rm{22}}}}{{\rm{O}}_{{\rm{11}}}}\left( {{\rm{aq}}} \right)\)

4. Conversion of maltose into glucose: The enzyme maltase converts maltose into glucose.

\({{\rm{C}}_{{\rm{12}}}}{{\rm{H}}_{{\rm{22}}}}{{\rm{O}}_{{\rm{11}}}}\left( {{\rm{aq}}} \right){\rm{ + }}{{\rm{H}}_{\rm{2}}}{\rm{O}}\left( {\rm{l}} \right) \to {\rm{2}}{{\rm{C}}_{\rm{6}}}{{\rm{H}}_{{\rm{12}}}}{{\rm{O}}_{\rm{6}}}\left( {{\rm{aq}}} \right)\)

5. Decomposition of urea into ammonia and carbon dioxide: The enzyme urease catalyses the decomposition of urea into ammonia and carbon dioxide.

\({\rm{N}}{{\rm{H}}_{\rm{2}}}{\rm{CON}}{{\rm{H}}_{\rm{2}}}\left( {{\rm{aq}}} \right){\rm{ + }}{{\rm{H}}_{\rm{2}}}{\rm{O}}\left( {\rm{l}} \right) \to {\rm{2N}}{{\rm{H}}_{\rm{3}}}\left( {\rm{g}} \right){\rm{ + C}}{{\rm{O}}_{\rm{2}}}\left( {\rm{g}} \right)\)

6. In the stomach, the enzyme pepsin converts proteins into peptides, while in the intestine, the pancreatic trypsin converts proteins into amino acids by hydrolysis.

7. Conversion of milk into curd: It is an enzymatic reaction brought about by the enzyme lactobacilli present in curd.

Enzymes Catalysis: Characteristics

Specificity: Enzymes are particular in their action on the substrate. Each enzyme catalyses only a specific type of reaction. For example, the enzyme urease hydrolyses urea to \({\rm{N}}{{\rm{H}}_3}\) and \({\rm{C}}{{\rm{O}}_2}\) but it does not hydrolyse \({\rm{N}}\)- methyl urea with a similar structure as urea. 

\({\rm{N}}{{\rm{H}}_{\rm{2}}}{\rm{CON}}{{\rm{H}}_{\rm{2}}}{\rm{ + }}{{\rm{H}}_{\rm{2}}}{\rm{O}} \to {\rm{2N}}{{\rm{H}}_{\rm{3}}}{\rm{ + C}}{{\rm{O}}_{\rm{2}}}\)

\({\rm{C}}{{\rm{H}}_{\rm{3}}}{\rm{NHCON}}{{\rm{H}}_{\rm{2}}}{\rm{ + }}{{\rm{H}}_{\rm{2}}}{\rm{O}} \to \) No reaction

The specific action of enzymes is due to the shape and shape/size of the cavity on the surface of the substrate.

Catalytic efficiency: Enzymes are highly efficient catalysts. They speed up reactions up to \(10\) million times as compared to the uncatalysed reactions.

Very small quantity is sufficient to catalyse a reaction: Minimal amounts of enzymes can be highly efficient. For example, the enzyme rennin can coagulate over a million times the weight of milk protein. It is because the enzyme molecules get regenerated during their catalytic activity. A typical enzyme molecule may be regenerated a million times in one minute.

Optimum temperature and pH: The catalytic activity of an enzyme is maximum at a particular temperature and \({\rm{pH}}.\) The optimum temperature at which the human enzyme activity is maximum is about \({\rm{37}}{\mkern 1mu} ^\circ {\rm{C}}\) (\(310\,{\rm{K,}}\) the body temperature). Below this temperature, the enzyme catalysed reactions are slow, and above this temperature, enzymes get denatured and lose their activity. The effect of \({\rm{pH}}\) on the activity of enzymes is complex. However, most enzymes’ optimum \({\rm{pH}}\) is around \(5\) to \(9\) (neutral \({\rm{pH}}\,7\) is optimal for maximum enzymes). 

Enzyme, inhibitors: Enzymes are controlled by various mechanisms and very sensitive to inhibitors (catalytic poisons)—different inorganic and organic substances such as \({\rm{HCN}},\,{{\rm{H}}_{\rm{2}}}{\rm{S}},\,{\rm{C}}{{\rm{S}}_{\rm{2}}},\) etc., act as inhibitors for enzymes. In the presence of these substances, enzymes lose their activity.

Mechanism of Enzyme Catalysis

1. Enzymes have several cavities.
2. These cavities present on the surface of colloidal particles of enzymes.
3. These cavities are of characteristic shape and process active groups such as \({\rm{ –  N}}{{\rm{H}}_{\rm{2}}}{\rm{,  –  COOH,  –  SH,  –  OH}}\) etc.
4. These are the active centres on the surface of enzyme particles.
5. The reactant molecules have complementary shapes and then fit into the cavities like a key fit into a lock.
6. An activated complex is formed on active groups (\({\rm{ – N}}{{\rm{H}}_{\rm{2}}}{\rm{, – COOH, – SH, – OH}}\), etc,) which then decomposes to yield products. Thus, the enzyme-catalysed reactions may be considered to proceed into two steps.

Step I: Binding reactant to the enzyme to form an activated complex \(\left( {{\rm{E}}{{\rm{S}}^ * }} \right).\)

\({\rm{E}} + {\rm{S}} \to {\rm{E}}{{\rm{S}}^{\rm{*}}}\)

Step II: Decomposition of the activated complex to form the product.

\({\rm{E}}{{\rm{S}}^ * } \to {\rm{E}} + {\rm{P}}\)

Practice Exam Questions

Catalysts Used in Industries

Catalysts are very often used in the chemical industries to accelerate reaction rates to get maximum yields of the products in minimum time. A few common examples are given below:

Homogeneous Enzyme Catalysis

In homogeneous catalysis, catalysts are in same phase as the reactants. Enzymes are biological catalysts that contribute towards increasing the rate of reaction and tends to be specific for certain reactants and products. The reactant in an enzyme-catalysed reaction is called a substrate.

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Summary

Enzymes are complex nitrogenous organic compounds that are majorly produced by living plants and animals. Many enzymes have been obtained in a pure crystalline state from living cells. We have learned about the importance of enzymes in our daily lives, the mechanism of enzyme catalysis, the characteristics of enzyme catalysis, and examples of catalysts used in industries. 

Frequently Asked Questions

Frequently asked questions related to enzyme catalysis is listed as follows:

Q.3. What are the different types of catalysts?
Ans: The catalysts are of four types: Biocatalysts, heterogeneous, homogeneous, and heterogenised homogeneous catalysts.

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