NCERT Class 11 Biotechnology Biotechnology: Chapter 4 — Enzymes: Classification and Mode of Action
This chapter introduces enzymes as biocatalysts essential for biochemical reactions, both in vivo and in vitro. Enzymes are highly specific to their substrates and possess immense catalytic power, accelerating reactions without undergoing permanent change. While most enzymes are proteins, some catalytic RNA molecules, known as ribozymes, are an exception. The chapter details the structure of proteinaceous enzymes, noting that their activity can be influenced by conformational changes and denaturation. It also explains the necessity of cofactors for many enzymes, which can be organic molecules (coenzymes) derived from vitamins or metal ions. The holoenzyme is defined as the enzyme combined with its cofactor, while the protein component is termed apoenzyme. The text highlights the transient role of coenzymes in catalysis and lists several coenzymes, their precursor vitamins, and their functions, alongside metal ions that act as cofactors for various enzymes. This foundational understanding of enzymes is crucial for comprehending various biological processes within the scope of Biotechnology.
Quick info
| Board | CBSE / NCERT |
|---|---|
| Class | Class 11 |
| Subject | Biotechnology |
| Book | Biotechnology |
| Chapter | Chapter 4 — Enzymes: Classification and Mode of Action |
| Language | English |
| PDF type | NCERT Textbook |
| Session | CBSE 2026 |
| Reading time | 1 minute |
| Word count | 196 |
Learning outcomes
- Define enzymes and their role as biocatalysts.
- Understand the specificity and catalytic power of enzymes.
- Identify the protein nature of most enzymes and the exception of ribozymes.
- Explain the necessity and types of cofactors (coenzymes and metal ions).
- Differentiate between holoenzyme and apoenzyme.
- Recognize the transient role of coenzymes in catalytic reactions.
Vocabulary
| Word | Meaning |
|---|---|
| Biocatalysts | Substances that increase the rate of a biochemical reaction without itself undergoing any permanent chemical change. |
| Catalytic power | The ability of an enzyme to greatly enhance the rate of a chemical reaction. |
| Ribozymes | Catalytic RNA molecules. |
| Dalton | A unit of mass used to express atomic and molecular weights. |
| Conformational structure | The three-dimensional shape of a protein molecule. |
| Denaturation | The process where the three-dimensional structure of a protein is altered, leading to loss of function. |
| Cofactors | Non-protein chemical compounds required for an enzyme's biological activity. |
| Coenzyme | A complex organic molecule that acts as a cofactor, often derived from vitamins. |
| Holoenzyme | An enzyme containing its cofactor; the complete, catalytically active enzyme. |
| Apoenzyme | The protein component of a holoenzyme, lacking its cofactor. |
| Prosthetic group | A cofactor that is tightly bound to an enzyme, often through a covalent bond. |
| Vitamins | Organic nutrients required in small amounts in the diet, many of which serve as precursors for coenzymes. |
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Practice questions
- What are enzymes? Answer: Enzymes are biocatalysts that catalyze biochemical reactions.
- What is the general molecular weight range of enzymes? Answer: The molecular weight of enzymes ranges from about 2000 to more than one million Dalton.
- What is an exception to enzymes being proteins? Answer: Some catalytic RNA molecules called ribozymes are an exception.
- What is a holoenzyme? Answer: A holoenzyme is an enzyme plus its cofactor.
- Name two types of cofactors. Answer: Two types of cofactors are coenzymes (complex organic molecules) and metal ions.
- What is an apoenzyme? Answer: An apoenzyme is the protein component of a cofactor-requiring enzyme.
Frequently asked questions
What is the primary function of enzymes?
Enzymes act as biocatalysts, accelerating the rate of biochemical reactions within living organisms and in vitro.
Are all enzymes proteins?
No, while most enzymes are proteins, some catalytic RNA molecules called ribozymes are an exception.
What is the difference between a coenzyme and a metal ion cofactor?
A coenzyme is a complex organic molecule, often derived from vitamins, while a metal ion is an inorganic ion like Fe2+, Mn2+, or Zn2+.
What is a holoenzyme?
A holoenzyme is the complete, catalytically active enzyme, consisting of an apoenzyme (protein part) and its cofactor.
How do coenzymes participate in enzyme activity?
Coenzymes participate transiently in catalysis, acting as carriers of specific functional groups.
What is a prosthetic group in the context of enzymes?
A prosthetic group is a cofactor that is tightly bound to the enzyme protein, often through a covalent bond.
Can enzyme activity be affected by external factors?
Yes, the enzymatic activity of proteinaceous enzymes can be affected by their conformational structure and denaturation.
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NCERT Class 11 Biotechnology — Biotechnology — Chapter 4 — Enzymes: Classification and Mode of Action. Verified by NCERT Help Editorial Team. Reviewed on 29 Jul 2026. Last updated 10 Aug 2026.