1. Gene Regulation
A gene (DNA) is expressed when it is made into a functional product (protein/enzyme)

2. Gene Regulation
Only a small part of the genes in a cell are expressed at any given time
To be “expressed” a gene must be transcribed and translated
What controls when and/or if a gene is expressed?
Recall promoters—start transcription signals—that bind to RNA polymerase

3. Example in prokaryotes
E. coli bacterium
4288 genes in the organism
A cluster of 3 can be turned “off” or “on” together
Genes that operate together: operon
The genes in this example are expressed to break down the sugar lactose and are therefore known as the lac operon

4. Example
The lac genes are turned off by repressors and turned on by the presence of lactose
Operator: section of DNA that binds to repressor and prevents transcription
Repressor protein also has a site that binds to lactose…which then removes it from the operator
When lactose is broken down the repressor protein binds to operator again

5. Eukaryotic gene regulation
No operons in eukaryotes
Most eukaryotic genes are controlled individually and have regulatory sequences that are much more complex than those of the lac operon in prokaryotes

6. Eukaryotic gene regulation
Enhancers: regions of DNA that makes transcription more likely to happen
Promoter sequences: regions of DNA that bind with RNA polymerase to start transcription
TATA box: region of DNA just before genes that ensure transcription will take place
Transcription factors: proteins that help to position RNA polymerase during transcription

7. Development and Differentiation
Differentiation: cells must specialize in a multicellular organism
A series of genes—hox genes—control differentiation of cells in an embryo
Sometimes called “master control” genes
A mutation in one of these genes will change body plan of an organism
A very striking similarity exists in these genes in all animals