NEET Practice Questions (MCQs) with Answers & Solutions

(d) The DNA fragments separated on an agarose gel can be visualised after staining with ethidium

bromide. It is intercalating agent and a fluorescent agent. The stained DNA fragments are seen

bright orange coloured band under UV-light.

Thinking process Intercalation is the insertion of molecules between the planar bases of DNA. This

process is used as a method for analysing DNA. Intercalation occurs, when ligands of an appropriate

size and chemical nature fit themselves in between base pairs of DNA. These ligands are mostly

polycyclic, aromatic and planar and therefore often make good nucleic acid stains. Intensively

studied DNA intercalator include ethidium bromide, proflavine, etc.

(d) DNA ligases (genetic gum) are used in recombinant DNA technology to join two individual fragments of double-stranded DNA by forming phosphodiester bonds between them to produce a recombinant DNA (plasmid).

The restriction enzyme EcoRV recognizes the palindromic DNA sequence 5'-GATATC-3' and cleaves it to produce blunt ends (no overhanging bases). Other enzymes like SalI, XhoI, and HindIII produce sticky ends (overhanging bases) after cleaving DNA.

(d) I-Iind II is a restriction endonuclease. Restriction endonucleases are enzymes used for cutting of

DNA at specific locations.

Hind II was the first restriction endonuclease isolated by Smith Wilcox and Kelley in 1968. It was

found that it always cut DNA molecules at a particular point by recognising a specific sequence of six

base pairs.

(d) Taq polymerase is a thermostable DNA polymerase obtained from Thermus aquaticus.

Theimusaquaticus is a bacterium that lives in hot springs and hydrothermal vents.

The DNA molecule to which the gene of interest is integrated for cloning is called vector. It is a DNA molecule used as a vehicle to artificially carry foreign genetic material into another cell, where it can be replicated and/for expressed. A vector containing foreign DNA is termed as recombinant DNA.

Plasmid is a small fragment of DNA (about 10 Kbp size) that is physically separate form and can replicate freely of chromosomal DNA within a cell. It can clone small DNA fragments.

Cosmid-45 Kbp

BAC-300-350 Kbp

YAC-1 Mbp/1,000 Kbp-2,500 Kbp)

DNA fragments generated by restriction endonucleases can be separated based on their size using a technique called gel electrophoresis. It involves applying an electric field to separate DNA fragments through a porous gel matrix, with smaller fragments moving faster than larger ones.

(c) Algae is a plant and so its cell wall is made up of cellulose. Cellulase enzyme is needed for degradation of its cell wall.

The hypervariable regions of DNA have Variable Number of Tandem repeats (VNTRs) of short

nucleotide sequences which are specific for each individual (except for monozygotic twins). Variations

also occur due to mutations, small deletions or insertions. Therefore, DNA cut by a particular

endonuclease will have different lengths in different persons. This phenomenon is called Restriction

Fragment Length Polymorphism. It is the basis of genetic (or DNA) fingerprinting and is useful in

identifying individuals from their semen, blood or tissues or any other DNA sample and resolution of

parent hood disputes. Polymerase Chain Reaction (PCR) is also useful in genetic fingerprinting as it can

amplify the DNA sample even if available in a very small amount.