Question 1

What experimental results would indicate that the mutation lacIˢ is dominant to lacI⁺?

Accepted Answer

The answer of What experimental results would indicate that the...

Question 2

Regarding the trp operon,trpR- maps to a considerable distance from the structural genes.The mutation either inhibits the interaction with tryptophan or inhibits repressor formation entirely.In the presence of tryptophan in the medium,would you expect the trp operon to be transcriptionally active? Explain.

Accepted Answer

The answer of Regarding the trp operon,trpR- maps to a...

Question 3

The lac operon consists of three structural genes as well as the adjacent region of DNA known as the regulator.

Accepted Answer

The lac operon consists of three structural genes and an adjacent region of DNA that includes the promoter and operator, but the regulator is not part of the operon; it is a separate gene that codes for the repressor protein.

Question 4

Explain why lacOᶜ mutations are cis-acting while lacI mutations can be trans-acting.

Accepted Answer

The answer of Explain why lacOᶜ mutations are cis-acting while...

Question 5

What symbols are used to describe constitutive mutations at specific regions of the lac regulatory system?

Accepted Answer

The answer of What symbols are used to describe constitutive...

Question 6

Monod discovered that if tryptophan is present in relatively high quantities in the growth medium,the enzymes necessary for its synthesis are repressed.How does this occur?

Accepted Answer

The answer of Monod discovered that if tryptophan is present...

Question 7

What is an allosteric molecule?

Accepted Answer

The answer of What is an allosteric molecule?...

Question 8

The catabolite repression system in E.coli essentially represses the lac operon when glucose is present.What evolutionary advantage would favor evolution of such a system?

Accepted Answer

The answer of The catabolite repression system in E.coli essentially...

Question 9

Regarding the lactose utilization system in E.coli,a gratuitous inducer is a molecule that is chemically analogous to lactose and induces the operon,but is not a substrate for the enzymes of the lac operon.

Accepted Answer

A gratuitous inducer is a molecule that can induce the lac operon but cannot be metabolized by the enzymes of the operon. This allows for the control of the lac operon without affecting metabolism.

Question 10

State whether the following statement is true or false,then give your reasoning.The terminating "hairpin" loop occurs in the trp operon when sufficient tryptophan is present.

Accepted Answer

the hairpin loop terminates transcription.

Question 11

Regarding the lactose utilization system in E.coli,a constitutive mutant is one in which the three enzymes are produced regardless of the presence or absence of lactose.

Accepted Answer

A constitutive mutant in the lactose utilization system of E.coli would produce the three enzymes involved in lactose metabolism (beta-galactosidase, lactose permease, and transacetylase) regardless of whether lactose is present or not. Therefore, the statement is true.

Question 12

The enzyme permease cleaves the linkage between glucose and galactose residues in lactose.

Accepted Answer

Permease does not cleave the linkage between glucose and galactose in lactose; that function is performed by the enzyme lactase. Permease facilitates the transport of molecules across cell membranes.

Question 13

The trp operon is typically characterized as being both under negative control and repressible.

Accepted Answer

The trp operon is regulated by the trp repressor protein, which binds to the operator region and prevents transcription of the genes involved in tryptophan biosynthesis. This is an example of negative control. In addition, the trp operon is also repressible, meaning that the presence of tryptophan in the environment will cause the trp repressor protein to bind to the operator more strongly, further reducing transcription of the operon. Therefore, both negative control and repression are characteristic of the trp operon.

Question 14

Describe the positive control exerted by the catabolite activating protein (CAP).Include a description of catabolite repression.

Accepted Answer

The answer of Describe the positive control exerted by the...

Question 15

Regarding regulation of the trp operon,what might one appropriately call the amino acid tryptophan?

Accepted Answer

The answer of Regarding regulation of the trp operon,what might...

Question 16

Under a system of negative control,genetic expression occurs unless such expression is shut off by some form of regulator.

Accepted Answer

In a system of negative control, genes are expressed by default and are turned off or repressed when a regulator molecule, such as a repressor protein, binds to DNA and inhibits transcription.

Question 17

Within the control region of the trp operon is a section of DNA that is sensitive to levels of tryptophan in the system.What is the name of this region?

Accepted Answer

The answer of Within the control region of the trp...

Question 18

Attenuation is known to occur in the lac operon.

Accepted Answer

Attenuation is a regulatory mechanism known to occur in the trp operon, not the lac operon. It involves premature termination of transcription in response to tryptophan levels.

Question 19

The cAMP-CAP complex and RNA polymerase bind more efficiently to the lac operon together than either does alone.What term is applied to this increased efficiency of binding?

Accepted Answer

The answer of The cAMP-CAP complex and RNA polymerase bind...

Question 20

Under a system of positive control,transcription does not occur unless a regulator molecule directly stimulates RNA production.

Accepted Answer

Under positive control, a regulator molecule directly stimulates RNA production, thus the statement given in the question is true.

Quiz 16: Regulation of Gene Expression in Prokaryotes