Question 1

Which enzyme is responsible for hydrolyzing lactose into glucose and galactose in E. coli, and what is the significance of this reaction for the lac operon?

Accepted Answer

β-galactosidase; it provides glucose and galactose, which are used for energy, thereby inducing the lac operon.

Question 2

In the absence of lactose, what is the state of the lac operon in E. coli and why?

Accepted Answer

The operon is not transcribed because the repressor binds to the operator, blocking RNA polymerase.

Question 3

Which of the following best describes positive control of the lac operon?

Accepted Answer

CAP-cAMP complex binds to the promoter, enhancing RNA polymerase binding and transcription when glucose is absent.

Question 4

Which equation correctly represents the methylation of cytosine in DNA?

Accepted Answer

$$\mathrm{Cytosine} + \mathrm{CH}_3 \rightarrow \mathrm{5{-}Methylcytosine}$$

Question 5

A mutation in the gene encoding the lac repressor causes it to be unable to bind lactose. What is the most likely outcome for lac operon expression in the presence of lactose?

Accepted Answer

The operon will not be transcribed because the repressor remains bound to the operator.

Question 6

Which histone modification is most closely associated with transcriptionally active chromatin?

Accepted Answer

Acetylation of lysine residues on histone tails

Question 7

Which experimental technique is used to identify the DNA sequences bound by a specific transcription factor in vivo?

Accepted Answer

Chromatin immunoprecipitation (ChIP)

Question 8

What is the role of the TATA box in eukaryotic promoters?

Accepted Answer

It serves as a binding site for general transcription factors and helps position RNA polymerase II.

Question 9

Which of the following best explains how enhancers can regulate gene expression from a distance?

Accepted Answer

They interact with promoters via DNA looping, bringing transcription factors into proximity with the transcriptional machinery.

Question 10

Which of the following statements about genomic imprinting is correct?

Accepted Answer

Imprinting involves DNA methylation that leads to the silencing of either the maternal or paternal allele.

Question 11

Which of the following is a direct effect of histone acetylation on chromatin structure?

Accepted Answer

Loosening of chromatin, facilitating transcriptional activation.

Question 12

A eukaryotic gene is found to be transcriptionally silent. Which combination of histone modifications is most likely present at its promoter?

Accepted Answer

H3K9me3 and deacetylated H3

Question 13

Which of the following best describes the function of the Polycomb Repressive Complex 2 (PRC2)?

Accepted Answer

It methylates H3K27, leading to chromatin condensation and gene silencing.

Question 14

Which of the following is a key difference between promoters and enhancers in eukaryotic gene regulation?

Accepted Answer

Promoters are required for transcription initiation, while enhancers increase transcription efficiency and can act at variable distances and orientations.

Question 15

Which process ensures the maintenance of DNA methylation patterns after DNA replication?

Accepted Answer

Maintenance methylation by DNMT1, which recognizes hemimethylated DNA and methylates the new strand.

Question 16

A mutation prevents the formation of cAMP in E. coli. What is the expected effect on the lac operon when both lactose and glucose are absent?

Accepted Answer

The lac operon will not be transcribed because CAP cannot be activated without cAMP.

Question 17

Which of the following best describes the role of long non-coding RNAs (lncRNAs) such as Xist in gene regulation?

Accepted Answer

They recruit chromatin-modifying complexes to specific genomic loci, leading to gene silencing.

Question 18

Which of the following experimental approaches would you use to determine if a specific protein binds to a known DNA sequence in vitro?

Accepted Answer

Electrophoretic-mobility shift assay (EMSA)

Question 19

Which of the following is a direct consequence of histone deacetylase (HDAC) activity?

Accepted Answer

Decreased transcription due to chromatin condensation.

Transcriptional Regulation and Epigenetics: Study Notes for Cell Biology

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