1. Bellwork: How is gene regulation in prokaryotes and Eukaryotes similar
Bellwork: How is gene regulation in prokaryotes and Eukaryotes similar? How is it different?

2. Gene regulation and expression
Section 13.4

3. Gene regulation and expression
Why is gene regulation important?
Why do cells regulate which genes are used at a given time?

4. Prokaryotic gene regulation
Bacteria and prokaryotes do not need all of their genetic information transcribed at once
They only want to use the genes necessary for the cells to function
This allows bacteria to respond to changes in their environment
This is done through DNA binding protein, which regulate genes by controlling transcription
Some switch genes on, some turn them off

5. Operons An operon is a group of genes that are regulated together
Genes will have related functions
E-coli for example has 4238 genes
3 genes are clustered together, which allow the bacterium to use the sugar lactose as food
These 3 lactose genes are called the lac operon.

6. Promoters and operators
On one side of the operon’s three genes are two regulatory regions
Promoter: Site where RNA polymerase can bind
Operator: When a DNA binding protein called a repressor binds to DNA

7. The lac operon in e-coli
Lactose turns the operon on

8. Eukaryotic gene regulation
Most of the principles of gene regulation in prokaryotes also apply to eukaryotes
Most eukaryotic genes are however controlled individually, and have more complex regulatory sequences than with e-coli.
TATA box helps with DNA transcription
Made of 25 – 30 base pairs containing the sequence TATATA or TATAAA
Bind a protein that helps position RNA polymerase

9. Transcription factors
Transcription factors bind to DNA sequences in the regulatory regions of eukaryotic genes, and control the expression of the gene
Some enhance transcription by:
Open up tightly packed chromatin
Attract RNA polymerase
Others block access to genes, much like repressor proteins
Normally multiple transcription factors are required before RNA polymerase can bind to the DNA

10. Promoters in Eukaryotes
Promoters have multiple binding sites for transcription factors
Certain factors can activate scores of genes at once, changing patterns of gene expression
Other factors only respond to chemical signals
Steroid hormones are chemical messengers that enter the cell and bind to receptor proteins
These receptor complexes act as transcription factors, so one single chemical signal can activate multiple genes
The exit of mRNA from the nucleus, the stability of mRNA and the breakdown of a gene’s protein s can all also act as a regulating factor

11. Cell specialization
Everything is more complicated in Eukaryotes – why?
Our DNA contains the information for every cell in our body
Would liver enzymes need to be produced in your bone marrow? Keratin, a protein in hair follicles is not produced in blood cells, or your heart, lungs…
Cell specialization requires genetic specialization
Complex gene regulation makes this possible

12. RNA interference
Cells contain a lot of small RNA molecules that are unrelated to the three major groups of RNA
These small RNA molecules help regulate gene expression
They interfere with mRNA
Interference RNA molecule produce by transcription, produces double stranded hairpin loop
Dicer enzyme make small fragments of miRNA
miRNA attaches to proteins and forms silencing complex

13. RNA interference continued
RNA interference has made it possible for researchers to switch genes on and off at will
All they had to do was insert double stranded RNA
Can be used to study gene expression in the lab.
Holds the potential to cures for cancer and viruses, allowing us to treat currently incurable diseases

14. Genetic control of development
What controls the development of cells and tissues?
In a multicellular organism, all of the specialized cell types came from the same fertilized egg cell
How do the cells know which cell to become?
Cells undergo differentiation, and become specialized in structure and function as they develop
Studying genes that control development and differentiation is an exciting area of Biology

15. Homeotic genes
Edward B Lewis showed that specific groups of genes control the identity of body parts in the embryo of fruit fly
By mutating one of these genes, it was possible to have a fly with a leg growing out of it’s head
His work showed that there are a set of master control genes (Homeotic genes) that regulate organ development in specific parts of the body

16. Homeobox and Hox genes
Homeotic genes share a very similar 180 base DNA sequence – a homeobox
Homeobox genes code for transcription factors that activate other genes important for cell development and differentiation
Homeobox genes are expressed in certain regions
In flies, a group of homeobox genes, called HOX genes are located side by side in a cluster
These determine the identity of each segment of a flie’s body
Arranged in the exact order they ate expressed in the body

17. Hox genes This does not apply just to flies
Nearly all animals fit this rule
Master control genes are like switches that trigger particular patterns of development and differentiation in cells and tissues
Evidence that genes have descended from common ancestors

18. Environmental influences
Environment can play a role in cell gene expression
Temperature, nutrients, salinity for example can all effect gene expression
Metamorphosis of tadpoles to frogs – great example
Mixture of environmental and hormonal factors
Speed of metamorphosis can be influenced by environmental factors, which translate into hormonal changes.
Hormones function at molecular level