What effect does the treatment of the host cell with divalent cations have on the process of DNA entry into the bacterium?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Enhanced efficiency of DNA entry into the bacterium
DNA is hydrophilic and cannot pass through cell membranes by itself. To make bacteria take up a plasmid, the cells are first made ‘competent’ by treating them with a specific concentration of a divalent cation such as calcium. This increases the efficiency with which DNA enters the bacterium through pores in its cell wall.
Option (1) Alteration in DNA permeability — Incorrect. The treatment acts on the bacterial cell, which becomes ready to take up DNA. Nothing about the DNA itself is changed.
Option (2) Enhanced efficiency of DNA entry into the bacterium — Correct. The divalent cation treatment raises the efficiency of DNA entry into the bacterium.
Option (3) Reduced efficiency of DNA entry into the bacterium — Incorrect. This is the opposite of the real effect. The treatment is used precisely because it makes DNA entry easier.
NCERT Extract:
Competent Host (For Transformation with Recombinant DNA) – “Since DNA is a hydrophilic molecule, it cannot pass through cell membranes. Why? 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.”