Question 1

Which of the following best describes the function of a helix-turn-helix DNA-binding domain?

Accepted Answer

It consists of two α-helices connected by a turn, with one helix recognizing specific DNA sequences in the major groove.

Question 2

A mutation in the operator region of the lac operon prevents the repressor from binding. What is the most likely outcome?

Accepted Answer

The operon will be constitutively expressed, even in the absence of lactose.

Question 3

Which of the following is a key feature of zinc finger DNA-binding domains?

Accepted Answer

They require a zinc ion coordinated by cysteine and histidine residues for structural stability.

Question 4

In the context of negative control of gene expression, what is the role of a corepressor?

Accepted Answer

It binds to the repressor protein, enabling the repressor to bind the operator and block transcription.

Question 5

Which of the following best describes an operon?

Accepted Answer

A cluster of consecutive genes transcribed as a polycistronic mRNA under the control of a single promoter.

Question 6

What is the main difference between an operon and a regulon?

Accepted Answer

An operon is a cluster of genes transcribed together, while a regulon is a set of operons or genes controlled by the same regulatory protein.

Question 7

Which of the following scenarios is an example of positive control of transcription?

Accepted Answer

An activator protein binds to an activator-binding site, facilitating RNA polymerase binding to a weak promoter.

Question 8

Which of the following statements about allosteric regulation of transcriptional regulators is correct?

Accepted Answer

Allosteric effectors can either increase or decrease the DNA-binding affinity of regulatory proteins by inducing conformational changes.

Question 9

A bacterial cell is grown in a medium containing both glucose and lactose. Which regulatory mechanism will most likely prevent the expression of the lac operon?

Accepted Answer

Catabolite repression, a form of global control, will prevent lac operon expression until glucose is depleted.

Question 10

Which of the following best explains why activator proteins are necessary for some promoters in bacteria?

Accepted Answer

These promoters are poor matches to the consensus sequence, so RNA polymerase binds them weakly and requires activator proteins to facilitate binding.

Question 11

Which of the following is a real-life example of negative control by induction?

Accepted Answer

The lac operon being expressed only when lactose is present and the repressor is inactivated by allolactose.

Question 12

Which of the following statements about DNA-binding proteins is correct?

Accepted Answer

They often bind to inverted repeat sequences as homodimers.

Question 13

Which of the following best describes the function of a leucine zipper DNA-binding domain?

Accepted Answer

It contains regularly spaced leucine residues that hold two α-helices in the correct orientation to grip DNA.

Question 14

Which of the following equations best represents the relationship between the rate of transcription ($$R$$), the concentration of RNA polymerase ($$[RNAP]$$), and the presence of an activator ($$A) $$that increases binding affinity by a factor $$k$$?

Accepted Answer

$$R = k 	imes [RNAP]$$ when $$A is $$present, $$R = [RNAP]$$ when $$A is $$absent

Question 15

In Archaea, which of the following is a unique feature of transcriptional regulation compared to Bacteria?

Accepted Answer

Archaeal repressors can block the binding of TBP (TATA-binding protein) and TFB (transcription factor B) to the promoter.

Question 16

A mutation causes the maltose activator protein to lose its ability to bind maltose. What is the most likely effect on the mal operon?

Accepted Answer

The mal operon will not be transcribed, even in the presence of maltose.

Question 17

Which of the following best describes the concept of global control in bacterial gene regulation?

Accepted Answer

Coordinated regulation of multiple operons or regulons in response to a common signal, such as catabolite repression.

Question 18

Which of the following statements about effectors in transcriptional regulation is correct?

Accepted Answer

Effectors are small molecules that bind to regulatory proteins, altering their conformation and activity.

Question 19

A scientist discovers a new DNA-binding protein that binds to the major groove of DNA and requires two identical polypeptides for function. Which structural feature is this protein most likely to possess?

Accepted Answer

A homodimeric structure with each polypeptide containing a DNA-binding domain.

Microbial Regulatory Systems: DNA-Binding Proteins and Transcriptional Control

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