Gene expression/Transcription and Lac Operon

Question 1

Transcription regulation in bacteria involves what?

Answer 1

a single activator or repressor

Question 2

When does transcription and translation occur in prokaryotes?

Answer 2

simultaneously

Question 3

How does transcription and translation happen simultaneously in prokaryotes?

Answer 3

there’s no membrane bound organelles so mrna gets made and free floating ribosome converts to amino acids

Question 4

What is RNA polymerase made of?

Answer 4

R subunit core, has two beta, two alphas, 1 sigma and 1 omega factors

Question 5

What does the sigma factor do?

Answer 5

It positions the enzyme correctly at the promoter and leaves as initiation of the transcription factor occurs

Question 6

Are sigma factors specialized to promoters? explain what this means?

Answer 6

some sigma factors recognize diff promoters, so yes factors are specialized to promoters

Question 7

What are the two ways termination occurs?

Answer 7

factor independent termination
Rho dependent termination

Question 8

Describe how factor independent termination occurs?

Answer 8

If there’s GC rich rna they form a hairpin so weak A rich RNA causes it rna polymerase to be less stable on dna, bumps into hairpin and falls off

Question 9

How does Rho dependent termination work?

Answer 9

The Rho factor recognizes C rich sequence and releases RNA polymerase

Question 10

How do bacteria conserve energy?

Answer 10

They only make the enzymes required to produce lactose if it’s in the environment

Question 11

Whats a promoter?

Answer 11

DNA sequence where RNA polymerase binds to initiate transcription

Question 12

What are activators? What do they do?

Answer 12

are proteins that bring the RNA polymerase closer to the promoter by binding to activator binding sites, overall promote transcription

Question 13

What are repressors? What do they do?

Answer 13

Are proteins which block RNA polymerase from binding to the promoter and stops it from moving along RNA, they bind to operators

Question 14

If the activator doesn’t bind to the activator site what happens?

Answer 14

low-level/basal transcription

Question 15

What are allosteric effectors?

Answer 15

small molecules that bind to the
allosteric site of regulatory
proteins that bind to the activator site

Question 16

How do allosteric effectors promote or stop transcription?

Answer 16

If they bind to activator proteins they’ll cause confirmational chnage which lets it bind to activator site and promote transcription, they may also bind to the repressor which cause a change that stops it from binding to the operator

Question 17

What type of regulation involves a repressor?

Answer 17

negative regulation

Question 18

What type of regulation involves an activator?

Answer 18

positive regulation

Question 19

What is an operon?

Answer 19

linked genes under the control of a single promoter
* Functionally-related genes (eg: all involved in lactose metabolism)
* Genes are transcribed onto a single mRNA molecule
* Either all or none of the gene products (enzymes) will be synthesized

Question 20

What is the lac operon?

Answer 20

: Operon required for the transport and metabolism of lactose

Question 21

What are cis acting elements in the lac operon?

Answer 21

Promoter, operator, and genes Z, Y

Question 22

What is Z-?

Answer 22

inactive Z, no matter what won’t make beta glactosidase

Question 23

What is P-?

Answer 23

RNA polymerase can’t bind, everything after it won’t work

Question 24

What is Oc?

Answer 24

The repressor can never bind to the operator, so operon is on no matter what

Question 25

If there’s no lactose present in negtive regulation, what does the repressor do?

Answer 25

binds so operon is off

Question 26

If there is lactose present, what does the prepressor do?

Answer 26

allosteric effector binds to repressor, stops it from binding to operator, operon is on and inducible

Question 27

What are F’ plasmids?

Answer 27

plasmids that carry genomic dna

Question 28

How do we create a merozygote (a partial diploid)?

Answer 28

when we insert a F factor that has left the chromosome it’s integrated in and has picked up some genomic dna which is now an F’ plasmid into an existing bacterial cell (have two copies of dna!)

Question 29

What is an I- mutation, is it recessive or dominant, cis or trans?

Answer 29

inactive repressor, is recessive and trans

Question 30

What is an Is mutation? Is it dom or recessive, trans or cis ?

Answer 30

super repressor, dominant over I+, trans

Question 31

Oc is what to Is?

Answer 31

epistatic, masks effect and repressor can’t bid to operator in Oc.

Question 32

Do bacteria prefer glucose or lactose?

Answer 32

glucose

Question 33

If glucose s present what kind of expression do we get from the lac operon?

Answer 33

minimal

Question 34

If there’s no glucose present what kind of expression do we get from the lac operon?

Answer 34

enhanced

Question 35

How does glucose effect production of CAMP?

Answer 35

if there’s glucose it stops atp from turning into camp so you get low camp
if there’s no glucose you get high camp

Question 36

What is CAMP?

Answer 36

an allosteric effector for protein CAP

Question 37

What is CAP?

Answer 37

catabolite activator protein

Question 38

What does the CAP-CAMP complex do?

Answer 38

enhances transcription

Question 39

If high glucose how much CAMP do you get? Does CAP bind? What happens to transcription?

Answer 39

high glucose, no camp, so no cap, so reduced transcription

Question 40

If low glucose how much CAMP do you get? Does CAP bind? What happens to transcription?

Answer 40

Low glucose, more CAMP, more CAP, more expression