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Biotechnology: Principles and Processes – Class 12 Biology notes, important questions and MCQs

NCERT Class 12 Biology, chapter 9. Notes, key terms, important questions with answers and MCQs.

Chapter overview

Biotechnology uses living organisms and their enzymes to make useful products. Genetic engineering cuts and joins DNA using restriction enzymes and ligase, and introduces it into host cells via vectors.

Tools

Restriction endonucleases (e.g. EcoRI) cut at palindromic sites, often leaving sticky ends.
DNA ligase joins fragments; vectors like plasmids (pBR322) carry ori, selectable markers (ampR, tetR) and cloning sites.
Gel electrophoresis separates DNA by size; DNA is seen with ethidium bromide under UV.

Process

Isolate DNA → cut → amplify by PCR (denaturation, annealing, extension with Taq polymerase) → ligate into vector → transform host.
Selection by antibiotic resistance or insertional inactivation (blue–white screening with lacZ).
Bioreactors grow recombinant cells on a large scale; downstream processing purifies the product.

Key terms

Recombinant DNA: DNA formed by joining DNA from different sources
Palindrome: sequence reading the same on both strands in the 5′→3′ direction
PCR: polymerase chain reaction, amplifies DNA in vitro

Important questions with answers

Why is a heat-stable DNA polymerase used in PCR?2 marks

PCR repeatedly heats the mixture to about 94 °C to separate DNA strands. Taq polymerase from Thermus aquaticus is not destroyed at this temperature, so it can be used for many cycles.

How can DNA be made to enter a bacterial cell? Name two methods.3 marks

Making the cell competent by treating it with calcium ions and then heat shock (ice, 42 °C, ice), so DNA enters through pores; also micro-injection, gene gun (biolistics) for plants, or using disarmed pathogen vectors.

Describe the steps of recombinant DNA technology, from isolating the gene to obtaining the product.5 marks

(1) Isolate DNA: break cells with enzymes (lysozyme for bacteria, cellulase for plants, chitinase for fungi), remove RNA and proteins with ribonuclease and protease, and precipitate DNA with chilled ethanol. (2) Cut DNA and the vector with the same restriction enzyme to get matching sticky ends. (3) Amplify the gene by PCR if needed. (4) Join the gene into the vector with DNA ligase to form recombinant DNA. (5) Introduce it into a competent host cell (transformation) and select recombinants using antibiotic resistance or blue–white screening. (6) Grow the host in large bioreactors so the foreign gene is expressed. (7) Downstream processing: separate and purify the product, add preservatives and test it in clinical trials before marketing.

Quick revision

Taq polymerase is heat stable.
EcoRI cuts GAATTC.
Ori controls copy number.

Exam tips

In blue–white screening, recombinant colonies are white because lacZ is inactivated.
Know the features of a cloning vector: origin of replication (ori), selectable marker, unique restriction sites (cloning sites), and small size.

Practice MCQs

Enzyme that joins DNA fragments is
1. restriction enzyme
2. polymerase
3. helicase
4. ligase
Show answer
Answer: (d) ligase. DNA ligase.
PCR is used to
1. cut DNA
2. amplify DNA
3. stain DNA
4. translate DNA
Show answer
Answer: (b) amplify DNA. Amplification.
EcoRI recognises the sequence
1. GAATTC
2. GGATCC
3. AAGCTT
4. GTTAAC
Show answer
Answer: (a) GAATTC. GAATTC.
Taq polymerase is from
1. E. coli
2. Bacillus
3. Agrobacterium
4. Thermus aquaticus
Show answer
Answer: (d) Thermus aquaticus. Heat-stable.
The bacterium used to transfer genes into plant cells is
1. E. coli
2. Rhizobium
3. Bacillus
4. Agrobacterium tumefaciens
Show answer
Answer: (d) Agrobacterium tumefaciens. Ti plasmid.
In blue–white selection, recombinant colonies appear
1. blue
2. colourless and dead
3. red
4. white
Show answer
Answer: (d) white. lacZ inactivated.
DNA moves in gel electrophoresis towards the
1. cathode
2. both
3. anode
4. neither
Show answer
Answer: (c) anode. DNA is negatively charged.
In pBR322, a gene inserted into the BamHI site of tetR makes the recombinant cells
1. resistant to both antibiotics
2. sensitive to tetracycline but resistant to ampicillin
3. sensitive to ampicillin
4. unable to grow at all
Show answer
Answer: (b) sensitive to tetracycline but resistant to ampicillin. Insertional inactivation of tetR.

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Written by Kundali IQ from standard, well-established facts to help with revision. This is not an official NCERT publication; always read your textbook too.