NCERT Class 12 Biotechnology Biotechnology: Chapter 2 — Host–Vector System
This chapter, 'Host–Vector System,' from NCERT Class 12 Biotechnology, delves into the fundamental components of Recombinant DNA (rDNA) technology. It explains that rDNA technology is a two-component system requiring a compatible host and a vector. The chapter details the roles of both hosts and vectors in gene cloning. It highlights that a host must readily accept rDNA, avoid degrading it, and provide necessary enzymes for replication. E. coli is presented as the most common prokaryotic host, while Bacillus subtilis is noted for protein secretion. Yeast is identified as a widely used eukaryotic host. The chapter also introduces the concept of vectors as DNA molecules capable of self-replication within a host cell, essential for isolating, propagating, and manipulating genes for various applications in biotechnology.
Quick info
| Board | CBSE / NCERT |
|---|---|
| Class | Class 12 |
| Subject | Biotechnology |
| Book | Biotechnology |
| Chapter | Chapter 2 — Host–Vector System |
| Language | English |
| PDF type | NCERT Textbook |
| Session | CBSE 2026 |
| Reading time | 3 minutes |
| Word count | 419 |
Learning outcomes
- Understand the two key components of Recombinant DNA technology: host and vector.
- Identify the characteristics and requirements of a suitable host organism for gene cloning.
- Recognize E. coli and yeast as common prokaryotic and eukaryotic hosts, respectively.
- Define the role and essential features of a vector in rDNA technology.
- Differentiate between various types of vectors like expression and shuttle vectors.
Vocabulary
| Word | Meaning |
|---|---|
| Recombinant DNA technology | A technique that involves joining DNA molecules from different sources to isolate, propagate, characterize, and manipulate genes. |
| Host | An organism that allows the entry and replication of recombinant DNA, providing necessary enzymes and proteins. |
| Vector | A DNA molecule, often a plasmid, that can replicate inside a host cell and carries the desired gene (insert). |
| Insert | The desired DNA molecule or target gene that is isolated from the source and inserted into a vector. |
| Gene cloning | The process of creating multiple identical copies of a specific gene or DNA segment using rDNA technology. |
| Plasmid | A small, circular, extrachromosomal DNA molecule found in bacteria that can be used as a vector. |
| Prokaryotic host | A host organism that lacks a membrane-bound nucleus and other organelles, such as bacteria (e.g., E. coli). |
| Eukaryotic host | A host organism with a membrane-bound nucleus and organelles, such as yeast. |
| Expression Vector | A type of vector designed to facilitate the expression of a cloned gene into a protein product. |
| Shuttle Vector | A vector capable of replicating in two or more different host species. |
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Practice questions
- What are the two main components of Recombinant DNA technology? Answer: The two main components are the host and the vector.
- Why is E. coli a commonly used host in gene cloning? Answer: E. coli is commonly used because it grows and reproduces rapidly, and genetically defined strains are available.
- What essential functions must a host cell provide for vector DNA replication? Answer: A host cell must supply all the required enzymes and proteins for the smooth replication of the vector DNA along with the insert.
- What is the primary role of a vector in gene cloning? Answer: The primary role of a vector is to act as a carrier DNA molecule into which the target gene (insert) is inserted, allowing for its replication and propagation within a host.
Practice MCQs
Q1. Which of the following is NOT a requirement for a host in gene cloning?
Explanation: A host should NOT consider recombinant DNA as foreign and degrade it; instead, it should facilitate its replication.
Q2. Which prokaryotic organism is most extensively used as a host for gene cloning?
Explanation: E. coli is highlighted as the most extensively used prokaryotic host in gene cloning due to its rapid growth and availability of defined strains.
Q3. What is the term for the desired DNA molecule isolated from the source in rDNA technology?
Explanation: The desired DNA molecule, generally termed as insert (target gene), is isolated from the source in the first step of rDNA technology.
Q4. Which eukaryotic organism is most widely used as a host in rDNA technology?
Explanation: Yeast is identified in the text as the most widely used eukaryotic host for gene cloning applications.
Q5. A vector must possess which essential characteristic to function in gene cloning?
Explanation: In principle, any molecule of DNA that can replicate itself inside a host cell can work as a vector for gene cloning.
Frequently asked questions
What is Recombinant DNA (rDNA) technology?
rDNA technology is a method used to join DNA molecules from different sources, aiming to isolate, propagate, characterize, and manipulate genes for various applications.
What are the two essential components for rDNA technology?
The two essential components are a compatible host organism and a vector (a carrier DNA molecule).
What makes E. coli a suitable host for gene cloning?
E. coli is suitable due to its rapid growth rate, ability to reproduce quickly, and the availability of genetically defined strains.
What is the function of a vector in gene cloning?
A vector acts as a carrier for the target gene (insert), allowing it to be introduced into a host cell and replicated.
Besides E. coli, what other prokaryotic host is mentioned for specific applications?
Bacillus subtilis is mentioned as an alternative host, particularly when the aim is the secretion of a protein encoded by a cloned gene.
What is the most common eukaryotic host used in rDNA technology?
Yeast is the most widely used eukaryotic host in rDNA technology.
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NCERT Class 12 Biotechnology — Biotechnology — Chapter 2 — Host–Vector System. Verified by NCERT Help Editorial Team. Reviewed on 29 Jul 2026. Last updated 10 Aug 2026.