To make host bacterial cells 'competent' to take up foreign plasmid DNA from the surrounding medium, the cells are treated with a divalent cation such as:
Answer and explanation
Correct answer: C. Calcium (), followed by a brief heat shock at
- Step 1: Because DNA is a hydrophilic, negatively charged polyanion, it cannot spontaneously traverse the hydrophobic phospholipid bilayer of bacterial cell membranes.
- Step 2: Treating bacterial cells with ice-cold divalent calcium ions () shields the negative charges of DNA and membrane lipopolysaccharides, facilitating DNA adhesion.
- Step 3: A brief thermal pulse (heat shock at for 90 seconds) followed by return to ice creates transient membrane pores that allow plasmid uptake.
Answer
Calcium (), followed by a brief heat shock at .
Why not the others: Monovalent sodium does not efficiently bridge divalent membrane phosphates; Freezing in liquid nitrogen lyses cells; Gamma radiation causes double-strand DNA breakage; Sonication shears plasmid DNA.
Practise more Biotechnology: Principles and Applications.
Free questions with an explanation for every one, and full timed NEET UG mock tests.
More Biotechnology: Principles and Applications questions
- Restriction endonucleases, often referred to as 'molecular scissors', cleave DNA molecules at specific recognition sites that typically exhi…
- In the standard naming convention for the restriction endonuclease EcoRI, what do the letters 'E', 'co', 'R', and the Roman numeral 'I' re…
- In the popular cloning vector , insertion of a foreign gene of interest at the BamHI restriction site causes insertional in…
- During agarose gel electrophoresis of DNA fragments, in which direction do the fragments migrate and how are they separated according to siz…
- Following agarose gel electrophoresis, DNA bands cannot be seen directly under visible light. What stain and illumination source are require…
- The process of cutting out a resolved DNA band from an agarose gel and extracting the purified DNA from the gel slice is termed: