Biotechnology: Principles and Processes — NEET UG practice

115 questions

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Sample questions with solutions

Q1 · 2026

Insertion of a foreign DNA at BamHI site in an E.coli cloning vector pBR322 results in the loss of antibiotic resistance towards:

  • A.

    Ampicillin and tetracycline

  • B.

    Ampicillin

  • C.

    Tetracycline

  • D.

    Gentamycin

Answer: C

  1. Understanding pBR322 — This plasmid vector carries two antibiotic resistance genes: one for ampicillin and one for tetracycline, along with unique restriction sites within these genes.

  2. Where BamHI cuts — The BamHI restriction site lies within the tetracycline resistance gene of pBR322.

  3. Effect of inserting foreign DNA — Given that the foreign DNA is ligated at the BamHI site, it disrupts the tetracycline resistance gene through insertional inactivation.

Foreign DNA at BamHI site→tetR gene disrupted\text{Foreign DNA at BamHI site} \rightarrow tet^{R} \text{ gene disrupted}

So, the recombinant plasmid loses its tetracycline resistance, while ampicillin resistance remains unaffected.

Hence, the answer is Option C: Tetracycline.

Q2 · 2026

Identify the correct sequence of steps in each cycle of Polymerase Chain Reaction :

  • A.

    Extension → Annealing → Denaturation

  • B.

    Annealing → Denaturation → Extension

  • C.

    Denaturation → Extension → Annealing

  • D.

    Denaturation → Annealing → Extension

Answer: D

  1. First step of PCR — Denaturation — The double-stranded DNA template is heated to a high temperature so that the two strands separate.

  2. Second step — Annealing — Since the strands are now single-stranded, the temperature is lowered so short primers can bind to their complementary sequences.

  3. Third step — Extension — Given that primers are now attached, DNA polymerase extends them by adding nucleotides to synthesize new complementary strands.

Denaturation→Annealing→Extension\text{Denaturation} \rightarrow \text{Annealing} \rightarrow \text{Extension}

Hence, the answer is Option D.

Q3 · 2026

Which of the following statements are not true regarding restriction endonucleases?

A. They are called molecular scissors.

B. These are the enzymes responsible for restricting the growth of bacteriophages in E. coli.

C. They cut the DNA only at the centre of the palindromic sites.

D. They remove nucleotides only from the ends of DNA fragments.

E. They recognise specific palindromic base-pair sequences.

Choose the answer from the options given below :

  • A.

    A and B only

  • B.

    A and E only

  • C.

    D and E only

  • D.

    C and D only

Answer: D

  1. Checking statement A — Restriction endonucleases cut DNA at specific sites, much like scissors cut paper, so they are indeed called molecular scissors. This statement is true.

  2. Checking statement B — These enzymes were first discovered because they restrict the growth of bacteriophages inside E. coli by cutting up the foreign viral DNA. This statement is true.

  3. Checking statement C — Restriction enzymes recognize palindromic sequences, but they usually cut the DNA slightly away from the exact centre of the palindrome, not precisely at the centre. This statement is false.

  4. Checking statement D — Removing nucleotides only from the ends of DNA fragments is the job of a different enzyme, a restriction exonuclease, not a restriction endonuclease. This statement is false.

  5. Checking statement E — Restriction endonucleases do recognise specific palindromic base-pair sequences. This statement is true.

Since statements C and D are the incorrect ones, hence the answer is Option D: C and D only.

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