Control of Gene Expression in Bacteria

Question 1

What does constitutive mean?

Answer 1

Always on, essential component of all living things

Question 2

What is inducible/Repressible? Why is it important?

Answer 2

Inducible = turned on
Repressible = turned off
Needed for cell growth under certain conditions

Question 3

DNA binding proteins

Answer 3

common in both euk and prok, can be activators or repressors of transcription through non covalent binding, binds to promoter which recruits or prevents RNA polly from interacting

Question 4

What is transcription in bacteria regulated by?

Answer 4

Operons - overlap with promoter and transcription start site

Question 5

What are negative regulatory proteins?

Answer 5

When binded inhibits transcription

Question 6

What are positive regualtory proteins?

Answer 6

When binded activates transcription

Question 7

Inducible operons

Answer 7

off->on

Question 8

Repressible operons

Answer 8

on->off

Question 9

Negative inducible

Answer 9

Regulatory protein is a repressor which blocks binding of polly to promoter, so an inducer binds to inhibitor to inactive it to turn on transcription (ex. metabolism)

An inducer binds to the inhibitor thats on the promoter and inactivates it turning transcription

Question 10

Negative Repressible

Answer 10

Regulatory protein is a repressor so it blocks binding of polly to promoter. To turn off transcription a cofactor/corepressor needs to bind to repressor to allow it to bind to promoter inhibiting transcription. (ex. biosynthesis)

So transcription is on and to turn it off a cofactor is needed to bind to the repressor so the repressor can bind to promoter inhibiting transcription.

Question 11

Positive Control

Answer 11

regulator protein is an activator, it binds to operon and induces transcription = CAMP or CAP catabolite activator protein

Question 12

CAMP or CAP catabolite activator protein

Answer 12

binds upstream promoter enhancing binding of RNA polly to promoter

Question 13

What is the lac operon?

Answer 13

negative inducible - regulatory protein is an inhibitor that must be turned on

Question 14

What inactivates the inhibitor in the lac operon? And what can it be metabolized by?

Answer 14

lactose, E.coli

Question 15

How does E.coli metabolize lactose?

Answer 15

Lactose gets transported across cell membrane by permase (LacY), then E.coli breaks lactose down into glc and gal that is catalyzed by B-galactosidase (lacZ) which can also convert lactose to allolactose. The third enzyme lacA (thiogalactoside) function is unknown.

Question 16

What is coordinate induction?

Answer 16

simultaneous synthesis of several proteins by an inducer

Question 17

What happens when no lactose is present? What binds to what inhibiting transcription?
What is lactose broken down by?
What binds to repressor causing repressor to be removed from operator?
What binds to promoter inducing the expression of Lac Z,Y,A?
What is lactose converted into?
What happens when lactose is depleted?

Answer 17

• Repressor protein (LacI) binds to operator (LacO) and inhibits transcription.
• Lactose is broken down by the little bit of B-galactosidase that is made.
• Allolactose binds to repressor and causes repressor to be removed from operator.
• RNA poly binds to promoter and induces expression of Lac Z,Y,A.
• Lactose in converted to glucose and galactose (and some allolactose to keep operon in on position).
• When lactose is depleted, no more allolactose is made and the repressor binds to operator inhibiting transcription.

Question 18

Regulation of expression can be in cis and trans, what is cis what is trans?

Answer 18

Cis - control gene expression is on the same piece of DNA
Trans - control gene expression on other DNA molecules

Question 19

What happens if bacteria has a mutation on Lacz- gene but not lacY+ gene in genome and mutation in LacY- gene but not LacZ+ gene in plasmid?

Answer 19

They are complimentary so the wild type will show and produce lactose

Question 20

What is LacI+?
What is produced and what can it bind to?
What does it repress in the absence of?
What happens when lactose is present?
Is the mutant repressor is dom or rec to wild type repressor?

Answer 20

• Trans dominant
• A repressor is produced and can bind to both operators
• It represses transcription in absence of lactose
• When lactose is present it inactivates the repressor and functional B-galactosidase is produced
• Therefore mutant repressor is recessive to wild type repressor.

Question 21

What happens if LacI has a mutation (LacIs)

Answer 21

It becomes insensitive to allolactose so the mutant repressor (LacIs) binds to operator in the presence/absence of allolactose.
Therefore the mutant repressor is dominant over wild type supprrepressor

Question 22

What happens when glucose is high in respect to CAMP levels?

Answer 22

Camp levels are reduced, reducing affinity of polymerase to promoter, reducing expression of the lac operon.