BT - Gene Regulation in Proks

Just think...

If the cell is able to get tryptophan (a necessary amino acid) from its environment, does the cell need enzymes necessary to make its own?

• Yes, the cell should make its own, because "homemade" tryptophan is always better

• No, the cell does should conserve the energy & resources it would take to make these enzymes and ultimately the tryptophan

In this example of an operon, what is the related function of all the trp genes?

• They code for enzymes to digest (break down) tryptophan

• They code for enzymes needed to synthesize tryptophan

• They code for the individual pieces of tryptophan

What is the job of RNA polymerase?

• replicate the DNA

• "read" the DNA and build the mRNA

• "read" the RNA and help build the protein

Which are true about the repressor?

• it is a regulatory protein

• when it binds to the operator region, transcription will proceed

• when it binds to the operator region, transcription cannot occur

• it is part of the operon DNA sequence

When there is no tryptophan available,

What is the normal state of the tryptophan repressor and the status of transcription?

• the repressor is active - it CAN bind to the operator - and transcription does not take place

• the repressor is inactive - it CANNOT bind to the operator - and transcription does take place

If lactose is not available, does the cell need to transcribe the lac genes?

• Yes

• No

For our purposes, think of lactose and allolactose as the same thing.  

Rewatch this segment if necessary.  When lactose is available and binds to the repressor, what happens?

• Lactose activates the repressor causing it to bind to the operator and transcription stops.

• Lactose inactivates the repressor so the repressor cannot bind to the operator and transcription proceeds.

What are the signaling molecules in these examples?

• The repressors

• The tryptophan or lactose present in the environment

• The operator

The operon systems utilized in prokaryotes are examples of 

• negative gene regulation

• positive gene regulation