$$[\text{Glucose}] \uparrow \Rightarrow [\text{cAMP}] \downarrow \Rightarrow \text{lac operon transcription} \downarrow$$

Question 1

Which statement best explains why genetically identical cells in a multicellular organism can perform different functions?

Accepted Answer

Cells selectively express different sets of genes through gene regulation mechanisms.

Question 2

During diauxic growth in E. coli, why does the growth rate temporarily slow after glucose is exhausted before resuming with lactose metabolism?

Accepted Answer

E. coli must synthesize new enzymes for lactose metabolism, which requires gene expression changes.

Question 3

Which of the following best describes the function of the lac operon in E. coli?

Accepted Answer

It enables the breakdown of lactose only when lactose is available and glucose is scarce.

Question 4

What is the role of the lac repressor in the lac operon system?

Accepted Answer

It binds to the operator to block transcription of the lac genes in the absence of lactose.

Question 5

Which equation correctly represents the effect of glucose on cAMP concentration and lac operon activation?

Accepted Answer

$$[	ext{Glucose}] \uparrow \Rightarrow [	ext{cAMP}] \downarrow \Rightarrow 	ext{lac operon transcription} \downarrow$$

Question 6

Which of the following is an example of feedback inhibition in the trp operon?

Accepted Answer

Tryptophan binds to the trp repressor, activating it to block transcription of trp biosynthetic genes.

Question 7

Which modification to histones is associated with increased gene expression in eukaryotes?

Accepted Answer

Acetylation of lysine residues by histone acetyltransferases (HATs)

Question 8

DNA methylation typically occurs at which sequence context and is associated with what effect on gene expression?

Accepted Answer

At CpG sites, leading to gene silencing

Question 9

In the agouti mouse model, how does maternal diet influence offspring phenotype through epigenetic mechanisms?

Accepted Answer

A diet rich in methyl donors increases DNA methylation of the agouti gene, resulting in brown, healthy offspring.

Question 10

Which statement best describes transgenerational small RNA inheritance in C. elegans?

Accepted Answer

Small RNAs induced by starvation are transmitted for at least three generations, affecting gene expression and lifespan.

Question 11

Which of the following layers of eukaryotic gene regulation involves the removal of introns and addition of a 5’ cap and poly-A tail?

Accepted Answer

RNA processing

Question 12

What is the primary function of miRNAs such as let-7 in gene regulation?

Accepted Answer

They block translation of target mRNAs, often acting as tumor suppressors.

Question 13

Which of the following best describes the effect of acetylation on histone proteins?

Accepted Answer

It neutralizes the positive charge on lysine residues, loosening chromatin and promoting gene expression.

Question 14

Which process allows for the temporary alteration of RNA sequences after transcription, potentially affecting protein diversity?

Accepted Answer

RNA editing by ADAR, converting adenosine to inosine

Question 15

A mutation in the 3’ untranslated region (UTR) of an mRNA most likely affects which aspect of gene regulation?

Accepted Answer

RNA stability, potentially reducing protein production

Question 16

Which of the following is a correct representation of an AND logic gate in the context of lac operon gene expression?

Accepted Answer

Gene expression occurs only when both lactose and cAMP are present.

Question 17

Which of the following is NOT a layer of eukaryotic gene regulation?

Accepted Answer

Feedback inhibition of metabolic enzymes

Question 18

Which real-world scenario best illustrates epigenetic inheritance?

Accepted Answer

Offspring of starved C. elegans exhibit increased lifespan due to inherited small RNAs.

Question 19

Which of the following statements about operons is true?

Accepted Answer

Operons allow coordinated expression of multiple genes under the control of a single promoter and operator.

Question 20

Which equation best describes the relationship between mRNA stability and protein production?

Accepted Answer

$$	ext{Protein Production} \propto 	ext{mRNA Stability}$$

Gene Regulation and Epigenetics in Prokaryotes and Eukaryotes

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