Chapter 18: Control of Gene Expression in Bacteria

Question 1

What are the 3 mechanisms of regulation in bacteria?

Answer 1

1. transcriptional control
2. translational control
3. post-translational control

Question 2

What is transcriptional control?

Answer 2

stops between DNA to mRNA
- changes mRNA lifespan

Question 3

What is translational control?

Answer 3

stops between mRNA to protein
- changes rate of translation

Question 4

What is post-translational control?

Answer 4

stops between protein to activated protein
- removes phosphate

Question 5

What does galactoside permease do?

Answer 5

transports lactose into the cell

Question 6

What does B-galactosidase do?

Answer 6

breaks down lactose

Question 7

What is an inducer?

Answer 7

small molecule that initiates transcription

Question 8

What did Jacob and Monod do?

Answer 8

• generate random mutations in E. coli
• study mutants with defects in lactose metabolism

Question 9

What do lacZ and lacY code for?

Answer 9

enzymes involved in metabolism

Question 10

What is lacI responsible for?

Answer 10

regulation of other genes

Question 11

What is an operon?

Answer 11

set of coordinately regulated bacterial genes that are transcribed together into one mRNA

Question 12

DEscribe negative control

Answer 12

repressor protein binds to DNA and shuts down transcription (on/off switch)

Question 13

Describe positive control

Answer 13

activator protein binds to DNA and triggers transcription (volume control)

Question 14

Describe the lac operon in its “off” state.

Answer 14

• default state
• lacI codes for the repressor protein
• repressor binds to the operator to prevent transcription
• dna sequence that overlaps with the promoter region

Question 15

Describe the lac operon in its “on” state

Answer 15

• lactose (inducer) binds to the repressor
• repressor changes shape, can no longer bind to DNA (allosteric regulation)

Question 16

When is the lac operon off?

Answer 16

when lactose is absent in the cell
- the repressor is bound to DNA and transcription stops

Question 17

When is the lac operon on?

Answer 17

when lactose is present in the cell
- lactose inducer binds to the repressor, repressor releases from DNA and transcription occurs

Question 18

When lactose is present, but lacI is mutated, what happens?

Answer 18

constitutive expression

Question 19

What is CAP?

Answer 19

• catabolite activator protein
• when bound to cAMP (second messenger), binds to DNA to increase transcription

Question 20

When is cAMP produced?

Answer 20

when glucose concentration is low

Question 21

High glucose concentration = __________ = _____________

Answer 21

low cAMP = low transcription of lac operon

Question 22

What is inducer exclusion?

Answer 22

glucose inhibits the activity of galactoside permease
- prevents lactose from entering the cell

Question 23

What is the trp operon?

Answer 23

• alternative negative control
• negative control of an anabolic pathway (synthesis of the amino acid tryptophan)
• transcription happens when trp is absent

Question 24

How do you turn off the trp operon?

Answer 24

• default is on

Off:
- trp co-repressor binds to the repressor
- repressor changes shape, now able to bind DNA

Question 25

What are regulons?

Answer 25

separate genes or operons with the same regulatory sequences that are controlled together

Question 26

What are 2 examples of regulons?

Answer 26

• SOS response (negative control)
  begins transcription of 40 genes to repair DNA
• ToxR (positive control)
  starts transcription when bacteria enters human gut