NEET Practice Questions (MCQs) with Answers & Solutions

(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.

In 1983 an American company Eli Lily produced the first genetically engineered insulin by first synthesizing two DNA sequences corresponding to A and B insulin chains. The two DNA sequences or genes were made to fuse with plasmids of Escherichia coli and later allowed to form Insulin chains. Rhizobium is a Gram negative, aerobic, motile, non-spore forming symbiotic nitrogen-fixing bacterium. It can fix nitrogen only when they are present inside the root nodules. Mycobacterium tuberculosis causes tuberculosis in man. It is an acute bacterial infection of the lungs, lymph and meninges.

Saccharomyces cerevisiae is known as Baker’s yeast and Saccharomyces ellipsoidens is wine yeast and these are used in baking and brewing industry respectively.

(a) DNA ligase is used to seal the nicks that remain in recombinant DNA molecule. Infact DNA ligase joins together the neighbouring nucleotides flanking a discontinuity in a DNA strand by forming a phosphodiester bond.  A recombinant DNA  molecules is a vector into which the desired DNA fragment has been inserted to enable its cloning in an appropriate host. Endonucleases are the enzymes that produce internal cuts called cleavage in DNA molecules. A class of endonucleases cleaves DNA only within or near those sites, which has specific base sequences, such endonucleases are known as restriction endonucleases. Exonucleases are enzymes that remove one or more nucleotide from the ends. DNA polymerase is the enzyme, which cause polymerization of nucleotides during DNA replication.

(a) Escherichia coli and Agrobacterium tumefaciens are the microbes found to be very useful in genetic engineering. E.coli is a motile, gram negative, rod shaped bacterium which is a normal inhabitant of human colon. It is most extensively used in bacterial genetics and molecular biology. Agrobacterium tumefaciens is a soil bacterium. It has Ti plasmid (Tumour inducing plasmid) and it can be used for the transfer of a desired gene in dicot plants.

Restriction endonuclease is a type of enzyme that can cleave molecules of DNA at a particular site

called Restriction site having polindromic sequence. These enzymes are produced by many bacteria

and protect the cell by cleaving and destroying the DNA of invading viruses. Now a days, restriction

enzymes are widely used in the techniques of genetic engineering.

(b) Plastids are semiautonomous cell organelles. They take part in storage and synthesis of organic compounds. Mitochondria are called the power houses of the cell as they are the centres of Kreb's cycle of respiration liberating the maximum amount of energy. Ribosomes are submicroscopic cell organelles manufacturing protein.

Plasmids are defined as autonomous elements, whose genomes exist in the cell as the extrachromosomal unit. These are the chromosomal elements found in bacteria. Plasmids are used as cloning vectors due to their increased yield potential.

(d) Technique of manipulating prokaryotic as well as eukaryotic DNA has witnessed a remarkable development. This has allowed breaking of a DNA molecule at two desired places to isolate a specific DNA segment and then its insertion in another DNA molecule at a desired position. The product thus obtained is called / DNA and the technique as genetic engineering.

(a) Restriction enzymes are endonucleases which cleave DNA at specific sites. They are originally extracted from the bacterium E.Coli. Type I restriction enzymes binds to a recognition site of a duplex DNA and cleave one strand only. Type II restriction enzymes are more valuable in gene manipulation and cleave the duplex at specific target sites at or near the binding site.

(d) T, plasmid is found extragenomically in Agarobacterium tumefaciens which possess T-DNA that is responsible for causing tumour in host plant.