Regulation of gene expression

Question 1

What is gene expression?

Question 2

What levels can gene expression be regulated?

Question 3

Why is it important that gene expression is regulated?

Answer 3

• enable cells to recognise and respond to environmental stimuli
• preserve energy and resources

Question 4

What are operons?

Answer 4

• the organisation of genes in bacteria
• genes coding for related proteins usually in one operon
• regulated by the same promoter

Question 5

What is the structure of an operon?

Answer 5

• Promoter
• Operator (can be before or after promoter). Where repressor proteins bind
• Regulator
• Structural genes

Question 6

How is gene expression regulated in bacteria?

Answer 6

binding of regulatory protein

Question 7

What is positive and negative gene expression?

Answer 7

• repressible operon
• inducible operon
• some operons are always turned on

Question 8

how are regulatory proteins regulated

Question 9

describe a simplified model of an inducible lac operon

Question 10

What does the 1-lacZ do in the lac operon?

Question 11

What does the 2-lacY do in the lac operon?

Question 12

What does the 3-lacA do in the lac operon?

Question 13

What are the regulatory components of the lac operon?

Answer 13

1 transcription regulator and 2 binding sites.

Question 14

Provide a summary of what happens when there is and isn’t lactose present.

Answer 14

Glucose present, no lactose present -> inhib protein expressed -> bound to operator region -> inhib. RNA Pol from transcribing structural genes.

lactose present -> repressor protein still made -> lactose can bind to repressor - > induce confirmation change take it off operator region -> RNA Pol can transcribe -> creared related enzymes

Question 15

What would happen is both glucose (usually preferred) and lactose if present?

Answer 15

Catabolite repression of lac operon: positive control

Question 16

What occurs during Catabolite repression of lac operon: positive control?

Answer 16

• lac operon will not be activated even is lactose present
• high glucose levels -> no cAMP -> operon doesn’t have support of the CAP-cAMP complex

(cAMP binds to CAP -> this complex binds to promotor region -> enhances RNA pol activity -> enable transcription)

Question 17

What is the system considered to be “leaky”?

Question 18

how is the lac operon regulated positively and negatively?

Question 19

How do proteins like CAP and repressor proteins bind to DNA?

Answer 19

Helix-turn-helix (dominant motif in E.coli)…

Question 20

What contribution did Jacob and Manod make to genetic evidence for the operator and repressor?

Answer 20

• in the 1960s
• discovered the operator, promotor and regulatory regions (rough mapping)

Question 21

What is the significance of 4 particular mutations in the lac operon?

Question 22

What is the O-negative lac mutation?

Answer 22

• 1st mutation
• in the operator sequence
• repressor can no longer bind ….

Question 23

What is the I-negative lac mutation?

Answer 23

• 2nd mutation
• in the repressor sequence
  …..

Question 24

What is the I-s lac mutation?

Answer 24

• 3rd mutation
• in the repressor sequence
  …..

Question 25

What is the P-negative lac mutation?

Answer 25

- 4th mutation - in the promotor sequence ....

Question 26

what is the trp operon?

Answer 26

- required for the synthesis of tryptophan - turned on when tryptophan is absent

Question 27

What are the 4 main components of the trip operon structure?

Question 28

What structural genes are in the trp operon?

Question 29

What is the default state of the trp operon?

Question 30

What happens to the trp operon when there is no tryptophan?

Question 31

How is the trp operon reset?

Question 32

What are the regulatory steps of the trip operon?

Question 33

What is transcription attenuation?

Answer 33

- doesn't involve DNA binding proteins - second control mechanism of trp operon ....

Question 34

What are the key sequences of trp mRNA?

Question 35

Attenuation