PROKARYOTIC EXPRESSION

Question 1

Why is it important to regulate gene expression?

Answer 1

• why produce unrequired proteins?
• important for differentiation in eukaryotic development
• transcription and translation are energy consuming processes
• genes/ protein products are often required in different environments
• genes/ protein products are often required in different quantities

Question 2

Majority of regulation is done at the ___ level.

Answer 2

transcriptional

Question 3

How is gene expression regulated post transcriptionally?

Answer 3

• folding of mRNA can prevent translation

- protein modification

Question 4

The strength of sigma 70 is based on the ____ ____, changing the probability that RNA polymerase is recruited.

Answer 4

binding sequence

Question 5

What is positive regulation?

Answer 5

uses transcriptional activators, so that gene is active in the presence of transcriptional factors
- 1 part of activator binds to DNA near promoter and another recruits RNA polymerase

Question 6

What is negative regulation?

Answer 6

gene is active in the absence of transcriptional factor

- bind to operator region and blocks access of RNA polymerase of inhibits its action

Question 7

What is an operon ?

Answer 7

• a cluster of genes regulated by a single promoter and expressed together as a unit

Question 8

Lac operon is _____ regulated by cap (___ ___ ___).

WHY?

Answer 8

positively

catabolite activating protein

• glucose is preferred energy source, occurs in low glucose conditions.

Question 9

What does laci do as a repressor?

Answer 9

• produces a product that normally binds to the operator (lacO), which blocks RNA polymerase

Question 10

When lactose is present what happens?

Answer 10

-lactose binds to laci, causing a conformational change meaning it can no bind to lacO and RNA polymerase can initiate transcription

Question 11

Laci repressor acts in ___, meaning it can spread to other operons.

Answer 11

trans

Question 12

LacO operates in __, meaning mutants are only affecting the specific operon.

Answer 12

cis

Question 13

What activates CAP?

- causes extra enhancement

Answer 13

cAMP
- binds to CAP and causes an allosteric change to allow RNA polymerase recruitment, becomes a promoter at alpha sub unit of RNA polymerase

Question 14

Function of Y gene in lac operon

Answer 14

permease

Question 15

Function of Z gene

Answer 15

to cut galactoside into galactose and glucose

Question 16

Trp operon is __(a)__ regulated by tryptophan, which binds to the _(b)__, activating it. The repressor then binds to operator to initiate __(c)__.

Answer 16

a) negatively
b) repressor
c) transcription

Question 17

How are the lac operon and trp operons different yet are still both negatively regulated?

Trp operon good example of ___ inhibition.

Answer 17

• Lac operon is inactive in the absence of lactose
• Trp operon is inactive in the presence of tryptophan
• feedback

Question 18

ara operon is ____ regulated

Answer 18

positively

Question 19

what are araBAD genes required for?

Answer 19

metabolism of arabinose

Question 20

max araBAD expression requires what?

Answer 20

a CAP

Question 21

When arabinose is present, binds to _(a)__ to recruit __(b)__ at _(c)___ region.

Answer 21

a) araC
b) Rna pol
c) initiator

Question 22

When arabinose is absent, araC has ___-(a)____ conformation and binds as dimer to operator (__(b)__) and inducer ((c)) regions.

Answer 22

a) anti- activator
b) araO
c) I1

Question 23

What are regulons? Used to respond to ?

Answer 23

groups of operons regulated together

• environmental fluctuations

Question 24

Different sigma factors are used to….

-Important sigma factor in heat shock regulation ?

Answer 24

direct R pol to different promoter sets

• sigma factor 32

Question 25

What is a constitutive mutant?

Answer 25

where the lack operons are ALWAYS active causing unregulated gene expression