Q: Which equation best represents the relationship between gene, message, and protein in molecular genetics?

$$\text{Gene} \xrightarrow{\text{transcription}} \text{mRNA} \xrightarrow{\text{translation}} \text{Protein}$$

Question 1

Which of the following best describes a constitutive gene?

Accepted Answer

A gene that is not regulated and is expressed continuously under normal cellular conditions.

Question 2

In the lac operon, what is the role of the operator region?

Accepted Answer

It is the binding site for regulatory proteins such as the lac repressor.

Question 3

Which mutation in the lac operon would result in constitutive expression of the operon?

Accepted Answer

lacO^c

Question 4

A partial diploid E. coli strain has the genotype: lacI+ P+ Oc lacZ+ lacY+ / lacI- P+ O+ lacZ- lacY-. Under what conditions will this strain make permease?

Accepted Answer

Constitutively

Question 5

In the absence of lactose, what happens to the lac operon in E. coli?

Accepted Answer

The repressor binds to the operator, blocking transcription.

Question 6

Which of the following is a structural gene in the lac operon and what is its function?

Accepted Answer

lacZ; encodes β-galactosidase, which breaks down lactose

Question 7

If a mutation occurs in the lacY gene (lacY-), what is the expected phenotype regarding lactose metabolism?

Accepted Answer

The cell cannot transport lactose into the cell.

Question 8

Which equation best represents the relationship between gene, message, and protein in molecular genetics?

Accepted Answer

$$	ext{Gene} \xrightarrow{	ext{transcription}} 	ext{mRNA} \xrightarrow{	ext{translation}} 	ext{Protein}$$

Question 9

Which of the following statements about regulatory genes is correct?

Accepted Answer

Regulatory genes encode proteins that interact with DNA sequences to regulate transcription and translation.

Question 10

In a lac operon mutant with a lacI^s (superrepressor) allele, what is the expected outcome for lac operon expression?

Accepted Answer

The operon is repressed in both the presence and absence of lactose.

Question 11

Which of the following is NOT an advantage of using bacteria for genetic studies?

Accepted Answer

They have diploid genomes, allowing for complex inheritance patterns.

Question 12

What is the function of allolactose in the regulation of the lac operon?

Accepted Answer

It acts as an inducer, binding to the repressor and preventing it from binding the operator.

Question 13

Which of the following best describes the difference between cis-acting and trans-acting elements in gene regulation?

Accepted Answer

Cis-acting elements are DNA sequences that regulate genes on the same DNA molecule; trans-acting elements are gene products that can regulate genes on different DNA molecules.

Question 14

A mutation in the lacP region (lacP-) of the lac operon would most likely result in which phenotype?

Accepted Answer

No transcription of the operon due to inability of RNA polymerase to bind.

Question 15

Which of the following is true regarding the dominance series of lacI alleles?

Accepted Answer

$$lacI^s \u003e lacI^+ \u003e lacI^-$$

Question 16

Which of the following scenarios would result in the expression of permease even when no lactose is present?

Accepted Answer

A mutation in the operator (lacO^c) that prevents repressor binding.

Question 17

Which of the following is an example of a negative inducible operon?

Accepted Answer

Lac operon

Question 18

In a partial diploid E. coli strain with the genotype: lacI+ O+ lacZ+ lacY- / lacI^s Oc lacZ- lacY+, under what conditions will this strain make permease?

Accepted Answer

Constitutively

Question 19

Which of the following best explains why every cell in an organism can have the same genomic sequence but different functions?

Accepted Answer

Different genes are used in each cell due to regulation of gene expression.

Regulation of Gene Expression in Prokaryotes: The Lac Operon

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