1. Gene Regulation
Packet #22

2. Prokaryotic vs. Eukaryotic
Why different?
Bacterial cells grow rapidly and have a relatively short life span
Eukaryotic have a long life span and because of that, they have the ability to respond to many different stimuli
Single gene is regulated in different ways in different cell types
Although transcriptional-level control is important, control at other levels of gene expression is also important

3. Transcriptional Regulation Prokaryotes
Most regulated genes in bacteria are organized into operons.
Operon
Gene complex consisting of a group of structural genes with related functions, plus the closely linked DNA sequences responsible for controlling them.
Set of adjacent structural genes whose mRNA is synthesized in one piece, plus the adjacent regulatory signals that affect transcription of structural genes

4. Operon
Each operon has a single promoter region upstream from the protein-coding region
The operator serves as the regulatory switch for transcriptional-level control of the operon.
Repressor Protein
Binds to the operator sequence
Prevents transcription
Although RNA polymerase binds to the promoter, it is blocked from transcribing he structural genes
When repressor is not bound, transcription proceeds

5. Inducible Operon The Lac Operon
Operon that is normally turned off
Repressor protein is synthesized in an active form that binds to the operator
If lactose is present, the repressor is converted to allow lactose to bind at an allosteric site on the repressor protein changing its shape.
The altered repressor cannot bind to the operator and the operon is transcribed.

6. Lac Operon II Positive vs. Negative Control
Repressible, and inducible operons are under negative control.
When the repressor protein binds to the operator
Transcription of the operon is turned off.
Positive Control
Separate protein binds to the DNA and stimulates transcription
CAP activates the lactose operon
Requires the use of cAMP.
Levels of cAMP increase as levels of glucose decrease.
CAP binds on the promoter region and stimulates the binding of RNA polymerase.

7. Repressible Operon Trp Operon
Operon that is normally turned on.
Repressor protein is synthesized in an inactive form
Cannot bind on the operator.
The end product acts as a corepressor.
When levels are high, corepressor binds at the allosteric site of the repressor
Repressor changes shape
Repressor binds on the operator
Transcription ends.

8. Constitutive Genes
These genes are neither repressible, nor inducible, but are active all times.
Housekeeping gene
CAP (catabolite activator protein) are produced constitutively
These proteins work by recognizing and binding to specific base sequences in the DNA.
The activity of constitutive genes, responsible for the production of CAP’s, is controlled by how efficiently RNA polymerase binds to their promoter regions

9. Gene Regulation in Eukaryotes
Already covered in the transcription packet.
Transcription factors

10. Homework Definitions Posttranscriptional controls DNA methylation
Gene amplification
Differential mRNA processing