FREE NEET Biology Practice MCQ Test: Biotechnology Principles And Processes Exercise 2 Questions Answers With Detailed Explanations [PDF]

Answer: (b)

The linking of antibiotic resistance gene with the plasmid vector became possible with DNA ligase. DNA ligase is an enzyme that is able to join together two portions of DNA and therefore plays an important role in DNA repair. DNA ligase is also used in recombinant DNA technology as it ensures that the foreign DNA is bound to the plasmid into which it is incorporated.

Answer: (a)

The presence of restriction sites within the markers tet r and amp r of plasmid permits an easy selection for cells transformed with recombinant plasmid. Insertion of the DNA fragment into the plasmid makes antibiotic resistance genes nonfunctional, for example, insertion of the DNA fragment into the plasmid (pBR322) using Pst I or Pvu I makes amp r nonfunctional. Bacterial cells containing such a recombinant pBR322 will be unable to grow in the presence of ampicillin, but will grow on tetracycline. This process, however, becomes burdensome because it requires simultaneous plating on two plates having different antibiotics. Thus, alternative selectable marker is developed to differentiate recombinants and non- recombinants on the basis of their ability to produce colour in the presence of a chromogenic substance. Here, a recombinant DNA is inserted in the coding sequence of an enzyme β-galactosidase. pUC 18 plasmid contains this gene which allows it to produce β-galactosidase which degrades certain sugars and produces a blue pigment when exposed to specific substrate analog. If the plasmid in the bacterium does not have an insert, i.e., is non- recombinant, the presence of chromogenic substrate gives blue coloured colonies. Presence of insert in the plasmid in recombinant bacterium does not produce any colour, such bacterial colonies are marked as recombinant colonies.

Answer: (d)

Ligase is a class of enzymes that catalyse the formation of covalent bonds using the energy released by the cleavage of ATP. Ligases are important in the synthesis and repair of many biological molecules, including DNA ligase and used in genetic engineering to insert foreign DNA into cloning vectors.

Answer: (d)

Answer: (a)

Answer: (d)

Answer: (d)

PCR is used only for amplification of DNA. It is not directly involved in Southern hybridisation technique.

Answer: (d)

In pBR322,

ori-represents site or origin of replication

rop-codes for proteins that take part in the replication of plasmid.

Hin d III, Eco RI- recognition sites of restriction endonucleases.

$amp^R$ and $tet^R$ - antibiotic resistance genes.

Answer: (a)

An antibiotic resistance gene in a vector acts as a selectable marker and usually helps in the selection of transformed bacterial cells.

Selectable markers in a vector help in identifying and eliminating non-transformants and selectively permitting the growth of the transformants.

Answer: (d)

Answer: (c)

Answer: (a)

Answer: (b)

A palindromic sequence is a nucleic acid sequence (DNA or RNA) that is the same whether read 5' (five-prime) to 3'(three prime) on one strand or 5' to 3' on the complementary strand with which it forms a double helix.

5' - GAATTC - 3'

3' - CTTAAG - 5'

It is a palindromic sequence of DNA cut by restriction enzyme EcoRI.

Answer: (a)

Restriction endonuclease are called “molecular scissors or biological scissors”. They recognize and cut double stranded DNA at specific points and are called palindromic sequences. Palindromic sequence are the ones which read same on both the strand in 5' → 3' direction. Same is true about 3' → 5' direction.

5' —— G ↓ AATTC —— 3'

3' —— CTTAA ↑ G —— 5'

Answer: (a)

PCR is a way to dramatically increase the numbers of a particular sequence of DNA (or an entire gene). This technique is most useful when cloning DNA since prior knowledge of the DNA sequence must first be obtained.

Answer: (c)

DNA ligase is an enzyme which can join the ends of two DNA chains by catalysing the synthesis of phosphodiester bond between 3' —OH at the one end of chain, and a 5' —phosphate group at the end of the other. Normally, joining of two molecules by the action of ligase is coupled with the breakdown of a phosphate bond as the formation of new phosphodiester bond requires energy.

Answer: (c)

Ethanol is much less polar than water. Adding it to the solution disrupts the screening charges exerted by water. The electrical attraction between phosphate and any positive ions (Na+) present in solution becomes strong enough to form a stable ionic bond and DNA precipitates. Ethanol precipitation is a widely used technique to purify, or concentrate nucleic acid.

Answer: (a)

Answer: (a)

Answer: (a)

Taq polymerase is a thermostable DNA polymerase named after the thermophilic bacterium Thermus aquaticus from which it was originally isolated.