NEET Practice Questions (MCQs) with Answers & Solutions

Probes are 15-30 bases long radioactive labelled oligonucleotides (RNA or DNA) used to detect complementary nucleotide sequences, used for disease diagnosis, etc.

Polymerase Chain Reaction (PCR) is used to amplify a DNA segment or to synthesize in vitro the multiple copies of gene (or DNA) of interest, using two sets of primers and the enzyme DNA polymerase. This enzyme is isolated from a bacterium Thermus aquaticus and it remains active during the high temperature but high temperature induced denaturation of double stranded DNA.

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.