Zoology MCQs for NEET — Practice Questions with Answers

Biolistics or gene gun is a direct or vectorless way used to introduce alien DNA into host cells. In this method of gene transfer, high velocity micro-particles of gold or tungsten, coated with DNA are bombarded on the plant cells.

Palindromic DNA is a base sequence of DNA, which reads the same forward or backward. It has similar sequence in both the strands. Different types of palindromic sequences are recognised by restriction endonucleases.

(c) Restriction endonuclease recognizes a particular palindromic sequence and degrades the same. It was so, called because it restricted the growth of bacteriophage in the bacterium (e.g., E.Coli). The convention for naming these enzymes is the first letter of the name comes from the bacterial genus; the second two letters come from te species, and the fourth letter from strain, eg., Eco RI comes from Escherchia coli RY13. Roman numbers following the names indicate the order in which the enzymes were isolated.

Gel electrophoresis is a technique to separate fragments of DNA. Since DNA fragments are negatively charged molecules they can be separated by forcing them to move towards the anode under an electric field through a medium/matrix. Now-a-days the most commonly used matrix is agarose which is a natural polymer extracted from seaweeds (e.g., Gelidium, Gracilaria, Gigartina, etc.).

(c) The palindromic base sequence is a sequence in double-stranded nucleic acids that reads the same on both strands when reading one strand from left to right and the other from right to left (i.e, both strands are read 5'$\to$3'). Out of the given options

           5'$-$GAATTC$-$3'

           3'$-$CTTAAG$-$5'

is a palindromic sequence that can be cut at about the middle by particular restriction enzyme.

Probe is a defined nucleic acid molecule that can be used in molecular hybridization procedures to

identify specific nucleic actd sequences that are complementary to it, by virtue of a label carried by

the probe. The label may be radioactive or non-radioactive. Nuclei add probes have a wide range of

applications such as in the detection of microorganisms in clinical specimens, in food and water

samples, in the detection of genctic diseases, etc.

(a) Restriction endonuclease recognizes a specific DNA base sequence (recognition sequence or recognition site, restriction sequence or restriction site) and cleaves both the strands of DNA at or near that site. The enzyme cuts the DNA, generating restriction fragments with overhanging ends or blunt ends.

(c) The uptake of foreign DNA or transgenes by plant cells is called transformation. A variety of techniques have been used to introduce transgenes into plant cells, these can be grouped into the following two categories - (i) Agrobacterium-mediated and (ii) direct gene transfers.

Agrobacterium tumemefaciens mediated transformation eliminates the need for regeneration from tissue explants.

(a) Introduction of DNA into plant cells without the involvement of a biological agent and leading to stable transformation is known as direct gene transfer. There are various methods for direct gene transfer, one of which is chemical method. Certain chemicals, eg, PEG (Polyethylene Glycol), polyvinyl alcohol and calcium phosphate enhances the uptake of DNA onto the outer surface of plasmalemma and the precipitate is taken up by the endocytosis.

(b) When genomic DNA extracted from any tissue of a plant or animal species is digested with a restriction enzyme, it is cleaved into segments. The segments of different sizes can be separated through gel electrophoresis. Gel electrophoresis involves the movement of fragments from a well created on one edge of the gel. Endonucleases are enzymes that produce internal cuts called cleavage in DNA molecules. A class of endonucleases cleaves DNA only within or near those sites, which have specific base sequences, such endonucleases are known as restriction endonucleases. The selected vector is cut open with a restriction enzyme that has a unique target site located in the sequence where the DNA insert should be integrated to facilitate the selection of recombinant DNA.