Biotechnology — Principles and Processes — Practice

Question 1

What is a restriction enzyme and why is it important in genetic engineering?

Accepted Answer

A restriction enzyme is a molecular scissor that cuts DNA at a specific palindromic recognition sequence. It is essential because it allows DNA to be cut precisely at known sites, enabling insertion of foreign genes into vectors.

Question 2

Name the three steps of PCR and their temperatures.

Accepted Answer

Denaturation at 95 C, annealing at 55-65 C, and extension at 72 C.

Question 3

Why is Taq polymerase used in PCR rather than ordinary DNA polymerase?

Accepted Answer

Taq polymerase, from the thermophile Thermus aquaticus, is heat-stable and survives the 95 C denaturation step, whereas ordinary DNA polymerase would be denatured and inactivated.

Question 4

What is the role of the selectable marker in a cloning vector?

Accepted Answer

It allows identification of cells that have taken up the vector; only transformed cells survive in the presence of the corresponding antibiotic, while untransformed cells die.

Question 5

What is blue-white screening and how does it work?

Accepted Answer

It selects recombinants. The cloning site lies within the lacZ gene. If no insert is present, lacZ is intact and colonies are blue on X-gal; if an insert disrupts lacZ, colonies are white. White colonies carry the recombinant plasmid.

Practice — Biotechnology — Principles and Processes

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