Question 1

Attenuation involves the termination of mRNA synthesis.

Accepted Answer

Attenuation is a regulatory mechanism found in bacteria that involves premature termination of transcription of the mRNA molecule. It occurs during transcription, not after mRNA synthesis.

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...

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

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

Accepted Answer

The trp operon is under the negative control of a repressor protein and is repressible, meaning that it can be turned off when tryptophan levels are high.

Question 5

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

Accepted Answer

Under positive control, transcription is stimulated by a specific regulator molecule called an inducer or activator. Without the presence of this molecule, transcription does not occur.

Question 6

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 7

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

Accepted Answer

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

Question 8

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 9

What is an allosteric molecule?

Accepted Answer

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

Question 10

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 11

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 12

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 indeed a molecule that induces the lac operon but is not a substrate for the enzymes of the operon.

Question 13

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

Accepted Answer

Permease is a type of transporter protein that facilitates the movement of lactose across the cell membrane; it does not cleave the linkage between glucose and galactose residues in lactose. The enzyme that cleaves this linkage is called lactase.

Question 14

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...

Question 15

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 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

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

In a constitutive mutant of E. coli, the genes for the three enzymes required for lactose utilization are constantly expressed regardless of the presence or absence of lactose. This leads to a continuous production of these enzymes.

Question 18

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 19

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 20

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...

Quiz 16: Regulation of Gene Expression in Prokaryotes