Microbial Regulation of Gene Expression

Question 1

Operon

Answer 1

A gene cluster transcribed as a single unit, controlled by the same elements, and which is coordinately transcribed and translated

Question 2

Operon Structure

Answer 2

• Regulatory gene (before the operon)

- Promoter -> Operator -> Structural Genes

Question 3

Allosteric proteins contain…

Answer 3

a catalytic (active) site and a regulatory (allosteric) site

Question 4

Repressor Protein

Answer 4

• Binds to the operator

- Prevents RNA Polymerase binding and turns off transcription

Question 5

Activator Protein

Answer 5

• Binds to activator site

- Enhances RNA Polymerase binding and turns on transcription

Question 6

Inducer

Answer 6

• Effector molecule that binds to repressors

- Results in transcription being turned on

Question 7

Activator

Answer 7

• Effector molecule that binds to activator proteins

- Results in transcription being turned on

Question 8

Constitutive Genes

Answer 8

• Expressed continually

- Not regulated

Question 9

Negative Control of Transcription

Answer 9

• Stops transcription using a repressor protein

- Repression and Induction

Question 10

Positive Control of Transcription

Answer 10

• Starts transcription using an activator protein

- Includes Catabolite Repression

Question 11

Global Control System

Answer 11

Coordination of expression of multiple genes and operons in response to the environment

Question 12

Trp Operon: No Trp

Answer 12

• Transcription is on
• Repressor cannot bind to operator
• Trp is synthesized

Question 13

Trp Operon: Trp

Answer 13

• Transcription is off
• Trp acts as corepressor and binds to repressor
• Repressor binds to operator and blocks polymerase

Question 14

Lac Operon: No Lactose

Answer 14

• Transcription is off

- Repressor is bound to operator, blocking polymerase

Question 15

Lac Operon: Lactose

Answer 15

• Transcription is on
• Lactose converted into allolactose, the inducer
• Allolactose binds to repressor, inactivating it
• β-galactosidase produced to cleave lactose into glucose and galactose

Question 16

Maltose operon is a…

Answer 16

…positive inducible operon

Question 17

Catabolite Repression: Lactose without Glucose

Answer 17

• Lack of glucose allows cAMP to be produced
• cAMP binds to CAP (catabolite activator protein) to activate it
• CAP binds to CAP binding site to allow polymerase to bind
• Transcription is on

Question 18

Catabolite Repression

Answer 18

Synthesis of unrelated, primarily catabolic enzymes are repressed when glucose is present

Question 19

Catabolite Repression: Lactose with Glucose

Answer 19

• Glucose inhibits cAMP synthesis and stimulates its transport out of the cell
• Without cAMP, CAP is inactive and cannot bind to DNA
• Without CAP on the DNA, polymerase cannot bind
• Transcription is off