Question 1

Which of the following best describes the role of a transcription activator in gene regulation?

Accepted Answer

It recruits RNA polymerase to the promoter and may remodel chromatin to increase gene transcription.

Question 2

A bacterial cell is exposed to a sudden increase in temperature. Which sigma factor is most likely to be activated to help the cell respond, and what is its primary function?

Accepted Answer

$$\$$sigma^{32}$$; activates heat-shock genes to protect against protein denaturation.

Question 3

Which mechanism allows a riboswitch to regulate gene expression in response to metabolite concentration?

Accepted Answer

By changing its mRNA structure upon ligand binding, which can terminate transcription or block translation.

Question 4

In the context of chromatin remodeling, what is the effect of histone acetyltransferase (HAT) activity?

Accepted Answer

It adds acetyl groups to histones, resulting in open chromatin and increased transcription.

Question 5

A mutation causes a bacterial anti-sigma factor to be nonfunctional. What is the most likely consequence for the cell?

Accepted Answer

The sigma factor will be constitutively active, potentially leading to inappropriate expression of stress-response genes.

Question 6

Which of the following best explains the 'rheostat' effect in gene regulation?

Accepted Answer

Multiple activators and repressors interact to fine-tune the level of gene expression, allowing for graded responses.

Question 7

How do microRNAs (miRNAs) typically silence gene expression in eukaryotic cells?

Accepted Answer

By binding to complementary mRNA sequences, leading to mRNA degradation or inhibition of translation.

Question 8

A researcher introduces a synthetic antisense RNA into a bacterial cell. What is the most likely outcome for the target mRNA?

Accepted Answer

The mRNA will be degraded or its translation will be blocked due to double-stranded RNA formation.

Question 9

Which of the following is a key feature of molecular clocks in cells?

Accepted Answer

They use a transcription–translation negative feedback loop to generate rhythmic cycles of gene expression.

Question 10

What is the primary function of second messengers in cellular signaling?

Accepted Answer

To transmit and amplify signals from cell-surface receptors to intracellular targets.

Question 11

A cell is exposed to a hormone that activates a G-protein coupled receptor. Which of the following best describes the sequence of events that follows?

Accepted Answer

The receptor activates a G-protein, which then triggers the production of second messengers, leading to changes in cellular activity.

Question 12

Which of the following scenarios best illustrates the function of a molecular thermometer in bacteria?

Accepted Answer

An RNA structure in the 5′ UTR unfolds at higher temperatures, allowing translation of heat-shock proteins.

Question 13

Which of the following is a direct function of long non-coding RNAs (lncRNAs) in gene regulation?

Accepted Answer

They recruit chromatin-modifying proteins or act as decoys to sequester miRNAs.

Question 14

A mutation in a bacterial cell prevents the degradation of an anti-sigma factor during stress. What is the most likely effect on gene expression?

Accepted Answer

The sigma factor will remain inactive, so stress-response genes will not be transcribed.

Question 15

Which of the following best describes the CRISPR-Cas system in bacteria?

Accepted Answer

It is an adaptive immune system that uses crRNAs to guide Cas enzymes to destroy foreign DNA.

Question 16

A gene is regulated by both an activator and a repressor. The activator increases transcription by recruiting RNA polymerase, while the repressor binds to the operator and blocks RNA polymerase. If both proteins are present at high concentrations, what is the most likely outcome for mRNA production?

Accepted Answer

The level of mRNA produced will depend on the relative strengths and concentrations of the activator and repressor, resulting in intermediate expression.

Question 17

Which of the following best explains how bistability in molecular switches can lead to two distinct cellular states?

Accepted Answer

Positive feedback allows the system to remain in either an 'on' or 'off' state even after the initial signal is gone.

Question 18

A scientist discovers a new small RNA in bacteria that binds to the ribosome-binding site of a specific mRNA, preventing translation. This RNA is most likely functioning as:

Accepted Answer

An antisense RNA.

Question 19

Which of the following is a key difference between miRNA and siRNA in eukaryotic gene regulation?

Accepted Answer

miRNAs are usually imperfectly complementary to their targets, leading to translational repression, while siRNAs are perfectly complementary and induce mRNA degradation.

lec 20:Molecular Regulation in Microbial Systems: Mechanisms and Examples

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