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 restriction endonucleases, DNA ligase, appropriate plasmid or viral vectors to isolate and ferry the foreign DNA into host organisms, expression of the foreign gene, purification of the gene product, i.e., the functional protein 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). Vectors used at present, are engineered in such a way that they help easy linking of foreign DNA and selection of recombinants from non-recombinants.
Identify the divalent cation which force the bacteria to take up the plasmid to make competent cells.
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Calcium
DNA is a large, hydrophilic molecule, so it cannot pass through the cell membrane easily. The bacterial cells are first made competent, that is, ready to take up DNA. This is done with a specific concentration of a divalent cation. The recombinant DNA is then forced in by a heat shock.
(1) Zinc — Incorrect. NCERT names calcium for this step.
(2) Copper — Incorrect. NCERT names calcium for this step.
(3) Calcium — Correct. It increases the efficiency with which DNA enters the bacterium through pores in its cell wall.
(4) Magnesium — Incorrect. NCERT names calcium for this step.
Note: This passage is taken from NCERT as it is. Most CUET (UG) questions come straight from NCERT, so study the book line by line, including figures and their titles.
NCERT Extract:
Competent Host (For Transformation with Recombinant DNA) – “… Since DNA is a hydrophilic molecule, it cannot pass through cell membranes.”
Competent Host (For Transformation with Recombinant DNA) – “… In order to force bacteria to take up the plasmid, the bacterial cells must first be made ‘competent’ to take up DNA. This is done by treating them with a specific concentration of a divalent cation, such as calcium, which increases the efficiency with which DNA enters the bacterium through pores in its cell wall.”