CHAPTER 14

Question 1

Gene Regulation

Answer 1

Ability to control the level of expression varies under different conditions

Question 2

The benefit of regulating genes

Answer 2

Only produced when required

Question 3

Constitutive

Answer 3

Genes that are unregulated
-Constant levels of expression
-Encode proteins necessary for survival

Question 4

What is the benefit of gene regulation?

Answer 4

It allows proteins to be produced only when required, optimizing resource use in the cell.

Question 5

How can gene regulation occur?

Answer 5

Regulation can occur at any stage in gene expression: transcription, translation, or posttranslational processing.

Question 6

Most common way of regulating genes in bacteria

Answer 6

Initiating transcription
-RNA synthesis can increase or decrease

Question 7

Two main types of regulatory proteins involved in transcriptional regulation

Answer 7

1- Repressors
2- Activators

Question 8

Repressors Proteins

Answer 8

-Bind to DNA
-Inhibit transcription
-Negative control

Question 9

Activators Proteins

Answer 9

-Bind to DNA
-Increase transcription
-Positive control

Question 10

Small Effector Molecules

Answer 10

-Affect transcription regulation
-Bind to regulatory proteins, NOT DNA directly

Question 11

Inducers

Answer 11

-Increase transcription
-Bind to activators and makes them bind to DNA
-Bind to reducers and prevents them from binding to DNA
-Called inducible genes

Question 12

What are repressible genes?

Answer 12

Genes that can be inhibited by corepressors, which bind to repressors to enable them to bind to DNA.

Question 13

What is the lac operon?

Answer 13

A regulatory unit in E. coli that consists of several structural genes and is controlled by one promoter, involved in lactose metabolism.

Question 14

Corepressors

Answer 14

-Inhibit transcription
-Inhibitors bind to activators and prevent the DNA binding
-Called irrepressible genes

Question 15

Absence of Inducer

Answer 15

The repressor protein blocks transcription

Question 16

Presence of Inducer

Answer 16

-Conformational change
-Repressor protein binds to DNA
-Transcription proceeds

Question 17

When can an activator protein bind to DNA

Answer 17

-Only binds to DNA if an inducer is present (bound to activator protein)
-Activates transcription

Question 18

What is the function of lacZ, lacY, and lacA in the lac operon?

Answer 18

-lacZ encodes β-galactosidase
-lacY encodes lactose permease
-lacA encodes galactoside transacetylase

Question 19

How does the lac repressor regulate the lac operon?

Answer 19

Without allolactose, the repressor binds to the operator site, inhibiting transcription. Allolactose induces the repressor to detach, allowing transcription to proceed.

Question 20

Catabolite Repression

Answer 20

A regulatory mechanism where E. coli prioritizes glucose over lactose when both are present, inhibiting the expression of the lac operon until glucose is depleted.

Question 21

How does cyclic AMP (cAMP) function in the regulation of the lac operon?

Answer 21

cAMP binds to the Catabolite Activator Protein (CAP), enhancing transcription when glucose is low.

Question 22

What is the trp operon?

Answer 22

A set of genes in E. coli involved in the biosynthesis of tryptophan, regulated by the trp repressor and leader peptide.

Question 23

How does tryptophan act in the regulation of the trp operon?

Answer 23

When tryptophan levels are high, it binds to the trp repressor, allowing it to bind to the operator and inhibit transcription.

Question 24

What is attenuation in the context of the trp operon?

Answer 24

A regulatory mechanism where transcription is prematurely terminated based on the availability of tryptophan, involving the formation of stem loops in mRNA.

Question 25

Riboswitches

Answer 25

RNA segments that can change conformation in response to small molecules, regulating gene expression by influencing transcription or translation.

Question 26

What role does feedback inhibition play in posttranslational regulation?

Answer 26

It prevents the overproduction of metabolic enzymes by inhibiting an early enzyme in a biosynthetic pathway when the final product accumulates.