1. Gene Regulation and Expression
3/29/2011

2. Prokaryotes Genes are regulated to conserve energy and resources
DNA binding proteins (called regulatory proteins – because they regulate gene expression) in prokaryotes regulate gene by controlling transcription
Some turn genes “on” – transcribe the gene
Some turn genes “off” – do not transcribe the gene

3. Prokaryotes cont…
Genes are organized into operons, a group of genes with related functions that are regulated together
An example of a prokaryotic operon is the E. coli’s Lac operon – 3 genes that must be turned on before E. coli can break down lactose for energy

5. Lac Operon
E. coli must transport lactose across its cell membrane to break lactose (disaccharide) down into its monomers galactose and glucose to get the energy from it
These tasks are performed by proteins coded for by genes of the Lac operon
The Lac operon genes are only expressed (transcribed and translated into protein) when lactose is present in the environment

6. Promoters and Operators
On one side of the operon’s 3 genes is a promoter (where transcription begins)
Then there is an operator region
This is where DNA binding protein, called the lac repressor protein, binds to DNA
The lac repressor blocks transcription by blocking RNA polymerase from reaching the genes to be transcribed

7. When Lactose is Present…
The lac repressor protein has a site where lactose can bind to it
When lactose binds the lac repressor protein, the repressor falls off the operator
Now that the lac repressor is no longer bound to the operator region, RNA polymerase can bind to the promoter and begin transcription of the lac operon genes which are needed to break down lactose

8. Eukaryotic Gene Regulation
Similar but more complex than prokaryotic gene regulation
Eukaryotic genes have what are called TATA boxes, short regions of DNA right before a gene that helps position RNA polymerase for transcription

10. Transcription Factors
DNA binding proteins called transcription factors control expression of genes
Some:
Enhance transcription by making DNA more accessible
Attract RNA polymerase
Block access to certain genes

11. Cell specialization requires genetic specialization
Complex gene regulation in eukaryotes is what makes specialization of cells possible

12. RNA Interference
miRNA are RNA molecules only a few dozen bases long, produced by transcription
These miRNA molecules attach to protein clusters and form a silencing complex
Binds to destroys mRNA which is complementary to it
“Sticks” to certain mRNA molecules and therefore blocks the translation of the mRNA
Blocking gene expression in this way is called RNA interference

14. Genetic Control of Development
During early stages of development, different sets of genes are regulated by transcription factors and repressors
The expression of different genes is what makes cells become specialized for specific functions (nerve, heart, muscle, etc)

15. Homeotic Genes
Master control genes which control and regulates the identifies of body parts, organs during development
Master control genes are like switches that trigger particular patterns of development and differentiation in cells and tissues

16. Homeotic genes all share a similar a DNA sequence called the homeobox
Homeobox Genes
Homeotic genes all share a similar a DNA sequence called the homeobox
These genes code for transcription factors that activate other genes important in cell development and differentiation

17. A group of homeobox genes
Hox Genes
A group of homeobox genes
Determines of each segment of an organism's body
All organisms share the same basic tools for building parts of the body
They are arranged in the exact order they are expressed “head to tail”

19. Environmental Influences
Factors such as temperature, salinity, population size, and nutrient availability can influence gene expression
Metamorphosis, such as in the bull frog, is regulated by internal (gene/hormonal) and external (environmental) factors