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151.

Which of the Ars operon regulation site is actually preventing RNA polymerase from binding and producing the Ara genes BAD?(a) O1(b) O2(c) P(d) ZThis question was addressed to me in a national level competition.My question is from Operons : Lac and Ara topic in chapter Gene Expression : Transcription Prokaryotes of Cytogenetics

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Correct CHOICE is (b) O2

For explanation I would say: Although O2 is much farther from the ara promoter P YET it can regulate P as it loops out and reaches the site. On the other hand O1 HOWEVER being closer doesn’t control the promoter of BAD genes.
Discussion
152.

You artificially increase the level of σ^32 in an E. coli culture. What will you expect to see?(a) rpo H transcription permanently inhibited(b) cdc transcription constitutively turned on(c) rpo H temporarily activated(d) cdc 6 permanently turned offThe question was posed to me in unit test.I'm obligated to ask this question of Transcription in Prokaryotes : Sigma Factor topic in portion Gene Expression : Transcription Prokaryotes of Cytogenetics

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Correct option is (c) rpo H TEMPORARILY activated

Easy explanation: σ^32 is necessary for transcribing genes like rpo H that helps in surviving heat shock while it doesn’t ACT on cdc6 that has a role in REPLICATION. As σ^32 is unstable it temporarily turns on rho H TILL the concentration RATIO of σ^32 and σ^70 returns to normal.
Discussion
153.

Rho dependent termination mechanism doesn’t reguire____________(a) ATP(b) Stem loop structure(c) G-C rich stem(d) Sigma factorI got this question in class test.Origin of the question is Transcription in Prokaryotes : Termination topic in chapter Gene Expression : Transcription Prokaryotes of Cytogenetics

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The CORRECT choice is (d) Sigma factor

The best explanation: Sigma factor plays no role in termination, rather it DISSOCIATES long before the RNA pol terminates. RHO however requires ATP for its rolling function and the stem loop structure formation. This stem loop structure is strengthened by G-C rich REGIONS in the stem.
Discussion
154.

Rho shows base preference although it doesn’t have any concensus cis binding sequence. Which region will be expected to bind Rho better?(a) G and C rich region(b) A and T rich region(c) Region rich in C and poor in G(d) Region rich in A and poor in TThe question was posed to me during an interview for a job.Question is taken from Transcription in Prokaryotes : Termination topic in division Gene Expression : Transcription Prokaryotes of Cytogenetics

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The correct choice is (c) Region RICH in C and POOR in G

For explanation I would say: RHO binds BEST to regions having high C CONTENT as much as 41% and low G content as much as 14%. As in RNA there is no compulsory base pairing the amount of G is not necessary equal to the amount of c.
Discussion
155.

Processivity of RNA polymerase is ________(a) Very high(b) High(c) Low(d) Very lowI had been asked this question in an online interview.This key question is from Transcription in Prokaryotes : Elongation in section Gene Expression : Transcription Prokaryotes of Cytogenetics

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The correct answer is (a) Very high

For explanation I would SAY: RNA POLYMERASE is highly processive as when the sigma subunit dissociates the DNA binding arm of RNA polymerase clamps shut around the DNA prevents it from falling off. DNA polymerase I on the other hand has low PROCESSIVITY.
Discussion
156.

In an experiment you use RNA polymerase without its sigma factor for transcription. What will be the result that you observe?(a) More transcription(b) Less transcription(c) More specific transcription(d) More random transcriptionI had been asked this question during an online interview.Question is from Transcription in Prokaryotes : Initiation topic in division Gene Expression : Transcription Prokaryotes of Cytogenetics

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The correct option is (d) More RANDOM transcription

The EXPLANATION is: Sigma SUBUNIT is responsible for recognizing the transcription start site. In its absence the RNA pol will transcribe at non-specific random sites. Sigma PLAYS no role in the rate of transcription so there is no chance in transcription rate in its absence.
Discussion