Unit 14

Question 1

What is the primary contributing factor associated with gene regulation in single-celled organisms like bacteria?

Answer 1

Changes in the environment

Question 2

What is a cis-acting regulatory element?

Answer 2

Elements that can control the expression of genes only on the same piece of DNA

Question 3

3. What is a trans-acting regulatory factor?

Answer 3

Regulatory factor able that can control the expression of genes on other DNA molecules

Question 4

What is an operon?

Answer 4

A group of bacterial structural genes that are transcribed together, along with their promoter and additional sequences that control their transcription

Question 5

What is an inducible operon system?

Answer 5

Transcription is normally off and must be turned on

Question 6

What is a repressible operon system?

Answer 6

Transcription is normally on and must be turned off.

Question 7

Define structural gene.

Answer 7

DNA sequence that encodes a protein that functions in metabolism or biosynthesis or that has a functional role in a cell

Question 8

What is the difference between a regulatory gene and regulatory element?

Answer 8

Regulatory genes encode a protein or RNA molecule that interacts with other DNA sequences to affect transcription or translation of those sequences, while regulatory elements are physically linked and affect transcription.

Question 9

What are the structural genes of the lac operon?

Answer 9

lacZ, lacY, lacA

Question 10

Is the lac I gene part of the lac operon? What protein does the lac I gene code for? What does that protein do?

Answer 10

No, it is a regulator gene that codes for a regulatory protein that in the absence of lactose, binds to the operator and inhibits transcription

Question 11

What does it mean to say that a gene is “constitutive”?

Answer 11

It is expressed continually without regulation

Question 12

When the repressor protein is bound to the operator sequence, are the genes of the lac operon on or off (that is, are the genes being transcribed, or not transcribed)?

Answer 12

Off, not transcribed

Question 13

What happens to the repressor protein when lactose (and thus, allolactose) is present?

Answer 13

It binds to the regulator gene making the protein inactive

Question 14

Describe the lac I- mutation

Answer 14

1. The lacI- mutation creates a mutant repressor that is incapable of binding to the lacO+ operator. In partial diploids however, as long as one of the copies of DNA has an normal lac I+ gene, then the active repressor can act as a trans regulator and activate the lacZ+ gene on the other DNA molecule.
2. The lacIS mutation produces a super-repressor that has a non-functional binding site for lactose. Meaning that it can’t be inactivated by an inducer and will bind to the lacO+ operon and inhibit transcription.

Question 15

Describe the lac Oc mutation

Answer 15

The lacOC mutation makes it incapable for the repressor protein to bind to the operator which results in constitutive transcription

Question 16

Describe the lac P- mutation.

Answer 16

The lacP- mutation results in the inability to synthesize β-galactosidase

Question 17

Describe the lacZ- mutation

Answer 17

The lacZ- mutation results in the synthesis on a nonfunctional β-galactosidase