Regulation Of Gene Expression

Question 1

When can regulation of gene expression occur

Answer 1

• before transcription
• during transcription (less mRNA produced)
• after transcription but before translation
• during translation
• after protein (inhibit protein function)

Question 2

What is negative regulation of transcription

Answer 2

The binding of repressor protein blocks transcription as it stops RNA polymerase from binding to promoter

Question 3

What is positive regulation of transcription

Answer 3

Binding of an activator protein stimulates transcription

Question 4

What is B-galactoside permease

Answer 4

Carrier protein, transports lactose into the bacterial cell

Question 5

What is B-galactosidase

Answer 5

Enzymes which hydrolyses lactose to glucose + galactose

Question 6

What are 3 specific proteins E. Coli produces uptake + metabolise lactose

Answer 6

• B-galactoside permease
• B-galactosidase
• B-galactoside transacetylase

Question 7

What is an operon

Answer 7

• unit of DNA
• share the same promoter
• have an operator

Question 8

What is a lac operon

Answer 8

Genes coding for lactose uptake/metabolism proteins are in a single DNA unit

Question 9

What type of regulation does the lac operon do

Answer 9

Negative regulation

Question 11

describe the repression of lac operon when lactose is absent

Answer 11

• repressor protein prevents transcription by binding to the operator
• RNA polymerase cannot bind to the promoter so transcription is blocked

Question 12

Describe the repression of the lac operon when lactose is present

Answer 12

• allolactose binds to the repressor which changes the shape of the repressor, it cannot bind to the operator so RNA binds to the promoter
• RNA polymerase can then transcribe the genes for the enzymes

Question 13

When glucose levels are low what type of regulation occurs increasing the efficiency of the lac operon transcription

Answer 13

Positive regulation

Question 14

Describe positive regulation of lac operon in low glucose

Answer 14

• a regulatory protein binds to cAMP (cyclic Adenosine MonoPhosphate) and the CRP-cAMP complex binds to the promoter
• RNA polymerase then binds more efficiently to the promoter
• the lac operon structural genes are transcribed

Question 15

Describe positive regulation of lac operon in high glucose

Answer 15

• cAMP is low, CRP is inactive and doesn’t bind to the promoter so RNA polymerase does not bind efficiently
• transcription of structural genes is reduced

Question 16

What are enhancers

Answer 16

Activiate / increase rate of transcription

Question 17

What are silencers

Answer 17

Bind factors that repress transcription

Question 18

Describe the action of enhancers

Answer 18

• specific TFs bind to enhancer + regulatory protein sites
• DNA bending allows specific TFs to interact with RNA polymerase complex + affect the rate of transcription

Question 19

Describe the stress response element (SRE)

Answer 19

• a stressor (ie.drought) activates transcription of a gene that encodes a transcription factor
• transcription factor binds to stress response element of each gene, which stimulates transcription of each gene that has the same SRE sequence
• the genes produce different proteins that have a role in the stress response