CH 8 Part 2 Gene Regulation in Bacteria

What is an Operon?

A unit of DNA that has a group of genes under the control of a single promoter.

During transcription what are the three components involved?

Promoter, RNA polymerase, and Termination Sequence.

What is the role of the promoter in transcription??

Initiates transcription of a gene.

What is the role of RNA polymerase in transcription?

Enzymes that copy DNA sequence into an RNA sequence.

What is the role of termination sequence in transcription?

Marks the end of the transcription.

What is the Bacterial Operon Promoter function?

• It is the region where RNA polymerase is going to bind

• Marks the start of the gene, but does NOT contain DNA that is expressed.

What is the role of the Operator in the operon?

• DNA sequence after the promoter that controls whether or not RNA polymerase will proceed

• Does NOT contain DNA that is expressed

What is the role of the genes in the operon?

• The genes are involved in the desired function

• They are all in a straight line one after another

• DNA is Expressed..

What is the termination sequence in the operon?

• They are the sequence where RNA polymerase disconnects from the DNA

• Marks the end of the transcribed gene, but does NOT contain DNA that is expressed..

Is the regulatory gene part of the Operon?

No it isn’t part of the operon.

What does the regulatory gene do?

• It’s constantly expressed in low amounts.

• It also produces a protein called the repressor.

Is the repressor active or inactive?

Well the repressor is active or inactive depending on the operon we are talking about.

What are Inducible operons? What is their default?

• Transcription is blocked

• Operons with an ACTIVE repressor need to be TURNED ON

• LAC Operon

What is a repressible operon? What is their default?

• Transcription is occuring

• Operons with an INACTIVE repressor need to be TURNED OFF.

• TRP Operon

Explain the LAC operon

Initially the repressor is active. And it’s binding to the operator. Which blocks the RNA polymerase from attaching to the promoter. Which means NO transcription is happening.

But now since lactose is present, it can bind to the active repressor and make it inactive. Now RNA polymerase can bind to the promoter and transcription will now occur!

Explain the TRP operon

The repressor is inactive. Now since there’s a lot of tryptophan, it’ll bind to the inactive repressor making it active.

Now the active repressor will bind to the operator making RNA polymerase detach from the promoter making transcription inactive.