1. A null repressor mutation (I-) in the lac regulatory system results in a. ind
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Question
1. A null repressor mutation (I-) in the lac regulatory system results in
a. inducible transcription.
b. constitutive transcription.
c. no transcription.
d. transcription but no translation.
e. no translation.
2. The attenuator region (AR) of the trp operon is located
a. within the promoter region.
b. after the structural genes.
c. between the operator site and the first structural gene.
d. within the operator site.
e. between the promoter region and the operator site.
3. In the eukaryotic GAL system, the physiologically regulated step is
a. None of these are correct.
b. import of the inducer molecule.
c. activity of the activation-domain of the transcriptional regulator.
d. DNA-binding by the transcriptional regulator.
e. feed-back inhibition by the end-product of the pathway.
Explanation / Answer
1) In absence of repressor inducer binds to operator and initiates the transcription. Hence option a is correct.
Constitutive transcription occurs when all the enzymes of lactose operon are continually expressed and carry out their function.
When repressor binds to the operator the transcription does not occur.
Transcription occurs but translation is prevented by alternative splicing and is observed in eukaryotes.
Translation blocked by regulatory elements binding to mRNA and is observed in eukaryotes.
2) The attenuator in trp operon is located between operator site and structural genes. Option c is correct.
3) In the eukaryotic GAL system, the physiologically regulated step is activity of the activation-domain of the transcriptional regulator. Option c is correct.
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