Chapter 18 AP BIO

What controls genes?

Operons.

What is an operator?

The 'switch' that controls DNA transcription.

What does an operator control?

1 to several related genes.

What is an operon?

Operator + promoter + genes.

What is a repressor?

The 'switch' protein that binds to the operator.

What happens if the repressor is attached to the operator?

The operon is repressed or 'turned off'.

What happens if the repressor is not attached to the operator?

The operon is not repressed or 'turned on', allowing for gene transcription.

Where are regulatory genes located?

Away from the operon.

What do regulatory genes do?

Code for repressor/switch proteins and continuously make the proteins.

What do repressible operons do?

Operons are turned on by default, but a repressor protein attaches to turn them off.

What happens when a repressor protein is turned off?

It blocks RNA polymerase attachment and is reversible.

What do allosteric proteins do?

When activated, corepressors inhibit transcription of a specific gene.

What are the qualities of inducible operons?

Operons are turned off by default, and repressors attach to the operator to turn them on.

What is an example of an inducible operon?

Lac operon.

What needs to happen when glucose is lacking but lactose is present?

Bacteria must change energy source and have enzymes to break down lactose.

What happens when glucose is lacking?

cAMP concentration increases.

What does cAMP do?

Activates CAP.

What is CAP?

An activator that binds to the promoter of the lac operon.

What does CAP do?

Increases affinity of RNA polymerase for the promoter of the lac operon.

What kind of control is the lac operon under?

Dual control.

What is the negative controller of the lac operon?

Lac repressor.

What does the lac repressor do?

Determines whether the lac operon is transcribed at all.

What is positive control of the lac operon provided by?

CAP.

What state is DNA found in in non-dividing cells?

Chromatin.

What are the two types of chromatin?

Heterochromatin and euchromatin.

What is heterochromatin?

Very tightly compacted chromatin.

What is euchromatin?

Less tightly compacted chromatin.

Why does histone modification occur?

Due to histones bonding with neighboring nucleosomes.

What happens in histone modification?

Chromatin becomes tightly compacted.

What occurs in histone acetylation?

Acetyl groups attach to histones, loosening heterochromatin into euchromatin.

What happens in DNA methylation?

Certain DNA bases become methylated.

What does DNA methylation do?

Prevents transcription.

What could DNA methylation be a cause of?

Cell differentiation.

What can DNA methylation be passed on through?

Cell division.