[Q41-42] For the following statements Mark A for True and B for False in respect

Question

[Q41-42] For the following statements Mark A for True and B for False in respect to gene expression in the lac operon. Ignore basal levels of expression. 41. Consider the following haplotype for the bacterial lac operon: I-0+Z+ There is also a plasmid with the following haplotype: +OZ- If there is no inducer present then functional B-gal will be produced. (T/F) 42. Consider the following haplotype for the bacterial lac operon: I-0+Z+ There is also a plasmid with the following haplotype: 1+0+Z- If glucose is present, there is no inducer, then functional B-gal will be produced (T/F) 43. The gels shown below could explain the results on an RNA and Protein gel if there was a mutation in SRP such that it would not bind the signal peptide on a nascent polypeptide. Mark A for True and B for False (T/F)

Explanation / Answer

I - Repressor binds to operator region and inhibits the expression of Z when no lactose is present. But, when lactose is present, repressor binds to lactose which allows the operator to initiate transcription of Z (galactosidase gene)

Z - Beta galactosidase enzyme is produced when lactose is present

O - Operator is the region where repressor binds when lactose is not present to prevent transcription of Z gene.

41) I- O+ Z+ / I+ Oc Z+ : True

I- is constitutive : repressor binds to operator even when lactose is present. But I+ is dominant to I-

OC is constitutive so, repressor cannot bind to stop transcription.Therefore, transcription of Z gene is always ON even when inducer is not present.

42) I- O+ Z+ / I+ O+ Z- : False

I- is constitutive which means that repressor binds to operator even when inducer is present. But I+ is dominant to I-. So, normal repressor is produced by means of I+ and it binds to operator only when inducer is not present.

Z+ is dominant to Z-

But when glucose is present and there is no inducer, beta gal is not produced.

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