Question 1

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

Accepted Answer

It consists of two alpha-helices connected by a short turn, where the recognition helix interacts specifically with DNA and the stabilizing helix maintains the structure.

Question 2

In the arginine operon, what happens when arginine is present in high concentrations?

Accepted Answer

The repressor binds the operator, blocking transcription and preventing unnecessary arginine synthesis.

Question 3

Which statement about allosteric regulation in transcriptional control is correct?

Accepted Answer

Allosteric effectors bind regulatory proteins, causing conformational changes that alter their ability to bind DNA.

Question 4

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

Accepted Answer

An operon consists of genes transcribed together from a single promoter, while a regulon is a collection of operons or genes regulated by the same regulatory protein but may be located at different sites on the chromosome.

Question 5

Which of the following is an example of negative control by induction?

Accepted Answer

The lac operon, where the presence of allolactose inactivates the repressor and allows transcription.

Question 6

Why do activator proteins often bend DNA when regulating transcription?

Accepted Answer

To facilitate the binding of RNA polymerase to weak promoters by bringing the activator-binding site closer to the promoter.

Question 7

Which DNA-binding domain is characterized by the use of a zinc ion interacting with cysteine and histidine residues?

Accepted Answer

Zinc finger

Question 8

A mutation prevents the maltose activator protein from binding maltose. What is the most likely consequence?

Accepted Answer

The maltose operon will not be transcribed even when maltose is present.

Question 9

Which of the following best describes the role of an inducer in transcriptional regulation?

Accepted Answer

It binds to a repressor protein, causing it to release from the operator and allowing transcription.

Question 10

Which statement about transcriptional regulation in Archaea is correct?

Accepted Answer

Archaeal repressors can block RNA polymerase binding or prevent TBP and TFB from assisting RNA polymerase.

Question 11

Which of the following is a consequence of constitutive expression?

Accepted Answer

The gene is expressed at approximately the same level under all growth conditions.

Question 12

Which equation best represents the relationship between the amount of protein produced and the levels of mRNA and translation efficiency?

Accepted Answer

$$ 	ext{Protein Amount} = 	ext{mRNA Level} 	imes 	ext{Translation Efficiency} $$

Question 13

Which of the following is true about homodimeric DNA-binding proteins?

Accepted Answer

They are composed of two identical polypeptides, each binding to an inverted repeat on DNA.

Question 14

A cell is exposed to a new sugar. Which regulatory mechanism is most likely to be used to express enzymes for its catabolism?

Accepted Answer

Positive control by induction, where an activator protein binds the sugar and activates transcription.

Question 15

Which of the following is NOT a level at which protein function can be regulated in microbial cells?

Accepted Answer

Genomic regulation by altering DNA sequence

Question 16

Which of the following best describes catabolite repression?

Accepted Answer

A global control mechanism that prevents the expression of genes for alternative carbon sources when a preferred source is available.

Question 17

Which of the following is a plausible effect of a mutation that prevents a repressor protein from binding its operator?

Accepted Answer

The operon will be constitutively expressed, regardless of the presence of the effector molecule.

Question 18

Which of the following is a correct statement about the major groove of DNA?

Accepted Answer

It is the main site for sequence-specific protein binding.

Question 19

Which scenario best illustrates the concept of a regulon?

Accepted Answer

Multiple operons scattered across the chromosome are all activated by the same regulatory protein in response to a single environmental signal.

Microbial Regulatory Systems: DNA-Binding Proteins and Transcriptional Control

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