BIOTECHNOLOGY : PRINCIPLES AND PROCESSES
Read the following passage carefully and answer the given questions.
Biotechnology deals with large scale production and marketing of products and processes using live organisms, cells or enzymes. Modern biotechnology using genetically modified organisms was made possible only when man learnt to alter the chemistry of DNA and construct recombinant DNA. This key process is called recombinant DNA technology or genetic engineering. This process involves the use of enzymes, viral vectors to carry the foreign DNA into host organisms, expression of the foreign gene, purification of the gene product, and finally making a suitable formulation for marketing. Restriction endonucleases are used in genetic engineering to form ‘recombinant’ molecules of DNA, which are composed of DNA from different sources/genomes. Gene cloning allows us to isolate and introduce only one or a set of desirable genes without introducing undesirable genes into the target organism. The ability to multiply copies of antibiotic resistance gene in E. coli was called cloning of antibiotic resistance gene in E. coli. In PCR, multiple copies of the gene (or DNA) of interest is synthesised in vitro using two sets of primers (small chemically synthesised oligonucleotides that are complementary to the regions of DNA) and the enzyme DNA polymerase.
Where does Eco R I cut the DNA when the sequence GAATTC is present in the DNA?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Between bases G and A only
A restriction enzyme recognises a specific palindromic sequence, which reads the same on both strands when read in the 5′ → 3′ direction. The enzyme cuts each strand at a fixed place inside it. EcoRI recognises 5′-GAATTC-3′. It cuts each strand between G and A, so it leaves short single-stranded overhangs called sticky ends.
(1) Between bases G and C only — Incorrect. G and C are the first and last bases of the site. They are not next to each other.
(2) Between bases G and A only — Correct. EcoRI cuts between G and A, and the cut on the other strand is made between the same two bases.
(3) Between bases A and A only — Incorrect. The two As are next to each other in the middle of the site, but EcoRI does not cut there.
(4) Between bases A and C only — Incorrect. There is no A next to a C in the sequence GAATTC.
Note: The passage is taken from NCERT. NTA has put lines of the NCERT text together to make it. Most CUET (UG) questions come straight from NCERT, so study the book line by line, including figures and their titles.