BGM1002/L17 Transcription Regulation

Question 1

How do cells react to changes in their environment? (2)

Answer 1

Changing sets of genes expressed
Changing the level at which they are expressed

Question 2

What is the key step for regulation of transcription?

Answer 2

Initiation

Question 3

Name the 2 strategies for regulation of transcription initiation.

Answer 3

Repression
Activation

Question 4

Describe how a repressor stops transcription initiation. (2)

Answer 4

Strong promoter sequence
Repressor binds to DNA and ‘turns it off’

Question 5

Describe how an activator allows transcription initiation. (2)

Answer 5

Weak promoter sequence
Activator binds to RNA polymerase and aids binding to promoter sequence

Question 6

What enzyme does lacZ encode?

Answer 6

Beta-galactosidase

Question 7

What enzyme does lacY encode?

Answer 7

Permease

Question 8

What enzyme does lacA encode?

Answer 8

Acetylase

Question 9

Define ‘polycistronic’.

Answer 9

A gene that encodes more than one protein

Question 10

When does high transcription of lac structural genes (lacZYA) occur?

Answer 10

Lactose present & glucose absent

Question 11

Define ‘operon’.

Answer 11

A cluster of genes under the control of a single promoter

Question 12

What is a constitutive promoter?

Answer 12

A promoter whose expression is not regulated and gives a set level of transcription

Question 13

How many amino acids is the lac repressor?

Answer 13

360

Question 14

Where does the lac repressor bind?

Answer 14

To the lac operator

Question 15

Describe the lac operator.

Answer 15

35 base pair palindrome

Question 16

What is the association constant of the lac operator?

Answer 16

2x10^13 M^-1

Question 17

What is the association constant of DNA?

Answer 17

2x10^6 M^-1

Question 18

Why is the lac repressor a tetramer?

Answer 18

It forms a DNA loop by binding to the primary operator and one of two secondary operators

Question 19

What is the inducer called for the lac operon?

Answer 19

Allolactose

Question 20

What can act as an inducer for the lac operon?

Answer 20

Other beta-galactosidases

Question 21

What occurs when allolactase binds to the lac repressor? (2)

Answer 21

DNA binding subunits separate by 3.6A
Affinity for operator reduced by factor of 1000

Question 22

What do glucose levels affect in cells? (2)

Answer 22

Inhibits adenylate cyclase
Prevents cAMP accumulation

Question 23

What is CAP/CRP?

Answer 23

Catabolite Activator Protein
cAMP receptor protein

Question 24

When does the CAP protein bind to the CAP binding site? (2)

Answer 24

When glucose levels are low
When cAMP levels are high

Question 25

Where is the CAP binding site located?

Answer 25

Just upstream of the -35 region

Question 26

How can high levels of recombinant proteins be expressed? (3)

Answer 26

Place gene of interest under control of lac repressor which inhibits expression
Grow cells
Induce expression by addition of IPTG which mimics allolactose