Question 1

Which of the following best describes the function of the operator in the operon model of gene regulation in bacteria?

Accepted Answer

It is a segment of DNA that acts as an on-off switch, controlling access of RNA polymerase to the genes.

Question 2

In the trp operon of E. coli, what happens when tryptophan is present in high concentrations?

Accepted Answer

Tryptophan acts as a corepressor, activating the repressor protein, which then binds to the operator and blocks transcription.

Question 3

Which of the following statements about the lac operon is correct?

Accepted Answer

The lac operon is an inducible operon that is usually off and is turned on by the presence of allolactose.

Question 4

A mutation in the lacI gene (which encodes the lac repressor) results in a nonfunctional repressor protein. What is the most likely consequence for the lac operon?

Accepted Answer

The lac operon will be constitutively expressed, and the enzymes for lactose metabolism will be produced even in the absence of lactose.

Question 5

Which of the following best explains why histone acetylation generally promotes transcription in eukaryotic cells?

Accepted Answer

Acetylation of histone tails loosens chromatin structure, making DNA more accessible to transcription machinery.

Question 6

A researcher finds that a particular gene is highly methylated in liver cells but not in nerve cells. What is the most likely effect of this methylation?

Accepted Answer

The gene will be inactivated in liver cells due to condensed chromatin structure.

Question 7

Which of the following mechanisms allows a single gene to code for multiple proteins in eukaryotes?

Accepted Answer

Alternative RNA splicing

Question 8

MicroRNAs (miRNAs) regulate gene expression by which of the following mechanisms?

Accepted Answer

Binding to mRNA and causing its degradation or blocking its translation

Question 9

A mutation in a proto-oncogene results in increased activity of the encoded protein. What is the most likely outcome?

Accepted Answer

The cell will have increased cell division, potentially leading to cancer.

Question 10

Which of the following best describes the role of tumor-suppressor genes?

Accepted Answer

They repair damaged DNA, control cell adhesion, and inhibit the cell cycle.

Question 11

In the context of embryonic development, what is the primary function of cytoplasmic determinants?

Accepted Answer

They influence early gene expression by being unevenly distributed in the egg, leading to differential gene expression in daughter cells.

Question 12

A fruit fly embryo whose mother lacks a functional bicoid gene develops with two posterior ends and no head. What does this observation support?

Accepted Answer

The bicoid gene product is required for establishing the anterior-posterior axis.

Question 13

Which of the following is an example of epigenetic inheritance?

Accepted Answer

Methylation of DNA that is inherited by daughter cells during cell division.

Question 14

Which of the following best explains why elephants have a much lower cancer rate than humans?

Accepted Answer

Elephants have 20 copies of the p53 gene, increasing their ability to suppress tumors.

Question 15

Which of the following is a key difference between prokaryotic and eukaryotic gene regulation?

Accepted Answer

Prokaryotes use operons for coordinated gene expression, while eukaryotes typically regulate each gene individually with multiple control elements.

Question 16

A scientist uses RNA interference (RNAi) to study gene function in a laboratory. Which molecule is most directly responsible for the gene silencing observed in this technique?

Accepted Answer

Small interfering RNAs (siRNAs)

Question 17

Which of the following best describes the role of enhancer sequences in eukaryotic gene regulation?

Accepted Answer

They are distal control elements that bind activator proteins to increase transcription of a specific gene.

Question 18

A patient inherits a mutant allele of the BRCA1 gene. What is the most significant implication of this inheritance?

Accepted Answer

The patient has an increased risk of developing breast cancer due to impaired tumor-suppressor function.

Question 19

Which of the following is a real-life example of positive gene regulation in bacteria?

Accepted Answer

The lac operon is activated by the binding of cyclic AMP receptor protein (CRP) to the promoter when glucose is scarce.

Question 20

Which of the following best explains how alternative RNA splicing can contribute to the complexity of the human proteome despite a relatively low number of genes?

Accepted Answer

It allows a single gene to be transcribed into multiple types of mRNA, each coding for a different protein variant.

Gene Expression and Regulation in Prokaryotes and Eukaryotes

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