NEET Biology PYQs and chapter-wise weightage

pBR322 is a commonly used cloning vector. When the gene for β-galactoside is inserted in the ampicillin resistance gene by using Pst I, the recombinant E.coli will lose ampicillin resistance due to insertional inactivation of the antibiotic resistance gene. The host (recombinant) cell will produce β-galactoside which is not a novel protein nor does it have the dual ability. The transformed cells cannot resist ampicillin as they have lost ampicillin resistance. A recombinant E. coli is produced and the host cell will not undergo lysis due to the insertion of the β-galactoside gene.

(a) Genetic engineering or recombinant DNA technology can be accomplished only if we have the key tools, i.e., restriction enzymes, polymerase enzymes, ligases, vectors and the host organism. (b) The sticky ends in DNA that result from the action of restriction endonucleases cannot be joined by the restriction enzymes, but by DNA ligases. (c) Restriction enzymes begin their action by first scanning the length of the DNA sequence and then recognising a specific sequence. This specific base sequence is known as the recognition sequence. (d) Each restriction endonuclease recognises a specific palindromic nucleotide sequence in the DNA.

EcoRI is the restriction enzyme which recognises 6 base pair palindromic sequences and cuts both the strands of DNA at second base in the sequence from 5’ end. It produces sticky ends. GAATTCCTTAAG