MBG CH3

What is the attenuator site?
a) A region where ribosomes bind to mRNA
b) A DNA sequence controlling transcription continuation or termination
c) A sequence coding for tryptophan
d) A protein that stops RNA polymerase

• a

• b

• c

• d

What determines whether transcription continues or stops in the trp operon?
a) Presence of glucose
b) Concentration of tryptophan and Trp-tRNATrp
c) Presence of lactose
d) The amount of mRNA produced

• a

• b

• c

• d

• What happens when tryptophan levels are high?
  a) The ribosome moves slowly, allowing 2-3 pairing
  b) The ribosome moves fast, preventing 2-3 pairing and forming 3-4 termination structure
  c) Transcription speeds up
  d) Transcription is unaffected

• a

• b

• c

• d

Which secondary structure allows transcription to continue?
a) 3-4 structure
b) 2-4 structure
c) 1-2 structure
d) 2-3 structure

• a

• b

• c

• d

What is the main difference between σ⁷⁰ and σ⁵⁴ promoters?
a) σ⁷⁰ is controlled only by activation, while σ⁵⁴ is controlled by repression
b) σ⁷⁰ is controlled by both repression and activation, while σ⁵⁴ is only controlled by activation
c) σ⁷⁰ and σ⁵⁴ are both controlled only by repression
d) σ⁷⁰ is found in bacteria, while σ⁵⁴ is in eukaryotes

• a

• b

• c

• d

• How does repression by steric hindrance work?
  a) It helps RNA polymerase bind more easily

• b) It removes the sigma factor from RNA polymerase

• c) A protein binds to the promoter, blocking RNA polymerase binding
  d) It increases the speed of transcription

• a

• b

• c

• d

What happens when tryptophan levels are low?
a) The trp repressor binds to the operator
b) RNA polymerase cannot bind to the promoter
c) The trp repressor is inactive, allowing transcription to occur
d) Tryptophan inhibits transcription

• a

• b

• c

• d

How does tryptophan regulate its own synthesis?
a) It acts as an activator for the trp operon
b) It binds to the trp repressor, activating it to block transcription
c) It speeds up the production of enzymes
d) It degrades the trp repressor

• a

• b

• c

• d

What is the function of tryptophan in the trp operon?
a) It acts as an inducer for transcription
b) It binds to the operator to initiate transcription
c) It acts as a co-repressor, activating the repressor to stop transcription
d) It prevents attenuation

• a

• b

• c

• d

Why is attenuation necessary in the trp operon?
a) The trp repressor alone is weak, so an additional regulation step is needed
b) It increases transcription efficiency
c) It ensures transcription happens even in high tryptophan conditions
d) It degrades the mRNA

• a

• b

• c

• d