The colonies of recombinant bacteria appear white in contrast to blue colonies of non recombinant bacteria because of :

[NEET 2013]

a)
Insertional inactivation of α-galactosidase in recombinant bacteria

b)
Non-recombinant bacteria containing β-galactosidease

c)
Inactivation of glycosidase enzyme in recombinant bacteria

d)
None of these

Correct answer is option 'B'. Can you explain this answer?

Question

The colonies of recombinant bacteria appear white in contrast to blue colonies of non recombinant bacteria because of :

[NEET 2013]

a)
Insertional inactivation of α-galactosidase in recombinant bacteria
b)
Non-recombinant bacteria containing β-galactosidease
c)
Inactivation of glycosidase enzyme in recombinant bacteria
d)
None of these

Correct answer is option 'B'. Can you explain this answer?

Accepted Answer

Alternative selectable markers have been developed which differentiate recombinant from non-recombinants on the basis of their ability to produce colour in the presence of chromogenic substrate. In this , a recombinant DNA is inserted within the coding sequence of an enzyme β-galactosidase. This results into inactivation of the enzyme, which is referred to as insertional inactivation. The presence of chromogenic substrate give blue coloured colonies of the plasmid in the bacteria does not have an insert. Presence of insert results into insertional inactivation of the galactosidase and the colonies do not produce any colour, these are identified as recombinant colonies.

Answer

It's beta galactosidase in ncert

Answer

The intact lacZ gene produce β-galactosidase, which cleaves X-gal and produces a blue color.
b)Recombinant bacteria containing a disrupted lacZ gene do not produce any β-galactosidase, so X-gal remains intact and produces a white color.

Answer

Answer should be (a)  i. e. gene for production of beta galactosidase is present in non-recombinant bacteria which produce chromogenic substance giving it blue colour.

Answer

The original plasmid with the gene for β-galactosidase will produce blue colonies due to the breakdown of X-gal, a chromogenic substrate that produces a blue color when β-galactosidase is present. Recombinant bacteria, on the other hand, have a disrupted β-galactosidase gene due to the insertion of foreign DNA, so they cannot break down X-gal and produce a blue color. Therefore, the colonies of recombinant bacteria appear white in contrast to the blue colonies of non-recombinant bacteria.

Answer

Answer should be 1option beta galactosidase responsible for colour check once

Answer

Presence of insert results into insertional inactivation of the alpha-galactosidase and the colonies do not produce any colour, these are identified as recombinant colonies.

• Alpha galactosidase is a glycoside hydrolase enzyme that hydrolyses the terminal alpha galactosyl from glycolipids and glycoproteins. It is encoded by GLA gene. Whereas beta galactosidase is an exoglycosidase which hydrolyses the beta glycosidic bond formed between a galactose and its organic moiety.

Answer

It should be recombinant bacteria not containing beta galactosidase

Answer

B

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