Trp Operon - Repression

Question 1

What are the two methods for regulating gene expression for the trp Operon?

Answer 1

1. Repression
2. Attenuation

Question 2

What does Repression do?

Answer 2

Repression blocks the initiation of transcription

Question 3

What is the trp Repressor?

Answer 3

It is a regulatory protein that controls gene expression for trp Operon

Question 4

Where does trp Repressor bind to?

Answer 4

The operator

Question 5

What is the Otrp (Trp Operator)?

Answer 5

A stretch of DNA (located after Promoter region and before start triplet) that acts as binding site for trp Repressor

Question 6

What is the 1st step in repression?

There is high levels of what?

Answer 6

There is high amounts of tryptophan in the cell

Question 7

What is 2nd step in Repression?

What becomes active and how?

Answer 7

Two available tryptophan molecules bind to trp repressor, causing active site of trp repressor to change shape.
trp Repressor is now active

Question 8

What is 3rd step in Repression?

What binds to what?

Answer 8

Active trp Repressor binds to operator region.

Question 9

What is 4th step in repression?

How is initiation of transcription halted?

Answer 9

Active trp Repressor that is now bound to operator physically blocks RNA Polymerase from moving down the operon and carrying out transcription.

Question 10

Describe the process of turning the operon on

Answer 10

• Little tryptophan in cell is available
• No tryptophan binds to trp repressor, which remians inactive
• Operator region remains unbound by repressor
• thus RNA polymerase can move down and transcribe