Match List I with List II: List I i. Genetically modified organism ii. Thermostable DNA polymerase iii. Ti plasmid iv. pBR322 List II a. Agrobacterium tumefaciens b. Bt cotton c. Thermus aquaticus d. Escherichia coli Choose the correct answer from the options given below:

i – b, ii – c, iii – a, iv – d

i – b, ii – a, iii – d, iv – c

i – a, ii – d, iii – c, iv – b

i – a, ii – b, iii – d, iv – c

The introduction of T-DNA into plants involves

infection of the plant by Agrobacterium tumefaciens.

allowing the plant roots to stand in water.

altering the pH of the soil, then heat shocking the plants.

exposing the plants to cold for a brief period.

Cloning Vectors

நகலாக்க கடத்திகள்

NCERT Class 12 · Biotechnology Principles and Processes · 6 NEET questions

Do not confuse a cloning vector with a simple DNA fragment. A vector is a vehicle; without the Origin of Replication (ori), it is just dead weight. NEET traps you by swapping 'ori' functions with 'selectable markers'. Know the difference.

The idea

Cloning vectors are DNA molecules, typically plasmids or bacteriophages, capable of autonomous replication within host cells. They must possess an 'ori' site to initiate replication, a selectable marker to identify transformants, and unique recognition sites for restriction enzymes. These features allow the insertion of foreign DNA for cloning purposes. The pBR322 plasmid is the standard model for understanding these essential components.

Why it matters

They act as vehicles to deliver and maintain foreign DNA inside a host organism for replication and protein production.

NEET lens

NEET frequently tests the specific features of pBR322, especially the antibiotic resistance genes acting as selectable markers. Memorize the restriction sites like EcoRI, BamHI, and SalI on pBR322. Do not waste time on non-NCERT vectors. Understand that 'ori' controls the copy number, a high-frequency question area.

Clinical significance

In medicine, cloning vectors are the backbone of recombinant DNA technology used to produce human insulin and growth hormones. If vector design fails, the expression of therapeutic proteins is impossible, leading to the failure of life-saving treatments. Precise vector engineering is the difference between a functional drug and a biological waste product.

Introduction

Cloning vectors are DNA molecules — usually plasmids or bacteriophages — that carry a foreign gene into a host cell and replicate there.

Core concept

Features (NCERT): (a) origin of replication (ori) — controls copy number; (b) selectable marker — e.g. genes encoding resistance to ampicillin, chloramphenicol, tetracycline or kanamycin for E. coli; (c) cloning sites — vectors should have very few, preferably single, recognition sites for commonly used restriction enzymes; (d) vectors for plants and animals. pBR322 is an E. coli cloning vector with ampR and tetR genes and ori. Plasmids are autonomously replicating circular extra-chromosomal double-stranded DNA. Agrobacterium tumefaciens, a pathogen of several dicot plants, delivers a piece of DNA called T-DNA into plant cells, transforming normal cells into tumour cells; its tumour-inducing Ti plasmid has been modified into a cloning vector that is no longer pathogenic. Retroviruses in animals have been disarmed and are used to deliver desirable genes into animal cells.

Go deeper

Natural pathogens have evolved ways to deliver genes into host cells; genetic engineers 'disarm' them and use them as vectors.

From Class 10

A vector is like a delivery van that carries a new gene into a cell and makes sure it gets copied.