Chapter 12: Regulation of Gene Expression in Bacteria and Bacteriophage

Question 1

What are three examples of transcriptional regulation?

Answer 1

Inducible regulation - lac operon
repressible transcription - trp operon
attenuation - trp operon and riboswitches

Question 2

What is constitutive transcription?

Answer 2

Constitutive genes are always transcribed

Question 3

What is regulated transcription?

Answer 3

proteins are only produced when the system needs it

Question 4

What is an inducible operon?

Answer 4

Genes must be turned on

default state = no transcription

ex: when substrate is present

Question 5

What is a repressible operon?

Answer 5

Genes must be turned off

always transcribed unless turned off

ex: when sufficient product is present

Question 6

What are the players of negative control of transcription?

Answer 6

Repressor
inducer OR corepressor

Question 7

Describe the effect of inducer in negative regulation

Answer 7

Binding of repressor protein blocks transcription

binding of inducer molecule to repressor protein allows transcription to occur

Question 8

Describe the effect of corepressor in negative regulation

Answer 8

binding of repressor-corepressor complex blocks transcription by negative regulation

with corepressor absent, repressor does not bind, allowing transcription

Question 9

What are the players of positive control of transcription?

Answer 9

Activator
effector OR allosteric inhibitor

Question 10

Describe the effect of allosteric effector compound in positive regulation?

Answer 10

Absense of effector prevents activator protein binding and transcription

effector binding to activator protein activates transcription by positive regulation

Question 11

Describe the effects of allosteric inhibitor compound in positive regulation?

Answer 11

Binding of inhibitor to activator protein prevents activator binding and transcription

absense of inhibitor allows binding of activator protein and activates transcription

Question 12

brief summary of lactose metabolism

Answer 12

Permease helps lactose into the cell

lactose is a disaccharide, must be broken down into two glucose by galactoside linkage

some lactose is changed to allolactose by B-galactosidase

Question 13

What genes make up the structural region of the Lac Operon?

Answer 13

LacZ
LacY
LacA

Question 14

What makes up the regulation region of the Lac Operon?

Answer 14

CAP binding site
lac operon promoter
operator
(lacl)???

Question 15

What enzyme is coded for by LacZ?

Answer 15

B-galactosidase

Question 16

What enzyme is coded for by LacY?

Answer 16

Permease

Question 17

What enzyme is coded for by LacA?

Answer 17

Transacetylase

Question 18

Describe the purpose of negative regulation in the lac operon?

Answer 18

negative regulation… is lactose present or not? Is yes, make enzymes!

Question 19

Describe the process of negative regulation in the lac operon when lactose is unavailable (glucose available)?

Answer 19

1 - lacl codes for the repressor protein.
2 - repressor protein binds to LacO, blocking RNA polymerase from transcription

Question 20

Describe the process of negative regulation in the lac operon when lactose is available (glucose unavailable)?

Answer 20

1 - lacl codes for the repressor protein.
2- allolactose is an inducer and binds to the repressor protein, blocking it from binding to LacO.
3 - RNA polymerase carries out transcription

Question 21

What is the purpose of positive regulation in the lac operon?

Answer 21

positive regulation… is GLUCOSE present or not? if Yes, use it as a better energy source!

Question 22

Describe catabolic repression in lac operon?

Answer 22

The lac operon will use all of it’s glucose until it’s gone (repressing catabolism of lactose), experiences a short lag time, then begins to use lactose

Question 23

Describe what happens at the CAP binding site on a lac operon?

Answer 23

CAP must bind to cAMP in order to increase the rate of transcription

When these two enzymes bind to CAP the levels of transcription are optimal

Question 24

Is the CAP binding site a form of positive or negative regulation?

Answer 24

positive regulation - need a binding of something to allow transcription

Question 25

Write the transcriptional conditions for the lac Operon?

Answer 25

yas

Question 26

What type of operon is the trp operon?

Answer 26

repressible operon

Question 27

Describe what happens to the trp operon when tryptophan is absent

Answer 27

repressor does not bind to trpO and transcription occurs

Question 28

Describe what happens to the trp operon when tryptophan is present?

Answer 28

tryptophan acts as a corepressor and binds to the repressor, which then binds to trpO and blocks transcription from occurring

Question 29

Describe the process of attenuation

Answer 29

three regions and 4 important genes
pause region (1&2), antitermination (2,3) and termination (3,4).

low trp&tRNA = ribosome stalls at uggugg, 2&3 pair, transcription continues

high trp&tRNA = leader mrna synthesised and transcription is terminated