Prokaryotic Gene Expression

Question 1

Operon

Answer 1

• A unit of linked genes that provide regulation for the transcription of genes downstream of it

Question 2

Promoter

Answer 2

• A portion of DNA that initiates transcription of a particular gene in the case of eukaryotes, but in the case of prokaryotes, the promoter can initiate transcription of multiple genes, with operons for regulation. The promoter and operon act in cis

Question 3

inducible system

Answer 3

• The system (in our case, most likely the transcription of some gene or multiple genes) is typically off unless there is some molecule present to cause the system to go, or to induce transcription
• Lac operon is an example of this: there is a repressor protein that sits on top of the operon, preventing RNA polymerase from transcribing. When lactose is present, it binds to the repressor, changing the repressor’s structure so it can no longer bind to the operon, causing it to fall off so transcription can proceed.
  There is a repressor gene somewhere upstream of the lac operon that codes for the repressor so the repressor molecule can be made

Question 4

Operator

Answer 4

• The part of the operon the repressor binds to?

Question 5

Cyclic AMP Regulation

Answer 5

• Prevents lac operon transcription when lactose is around but glucose doesn’t need to be produced.
• Adenylate Cyclase (AC) produces cAMP
• The presence of cAMP increases Catabolite Activating Protein (CAP) activity, which leads facilitates RNA polymerase binding
• Glucose inhibits AC, so cAMP can’t be made and RNA polymerase binding doesn’t happen, or at least doesn’t happen as easily

Question 6

Merozygotes

Answer 6

• Organisms that are diploid for only a select part of their genome, so we can add

Question 7

Repressive system

Answer 7

• A system (in our case, transcription) in which the system is typically constantly on unless there is some molecule to interfere with the system.
• The tryptophan operon is an example of this
• The repressor for the operon is inactive, unless tryptophan comes and binds to it. Then it changes its conformation so it can bind to the operator, preventing transcription
• This is how tryptophan is a product inhibitor: the tryptophan operon codes for tryptophan, and when enough tryptophan is present, it literally prevents the production of more of itself.