1. Chapter 15 Regulation of Gene Activity

2. Consider that....
Every cell of the body contains ALL the DNA for the organism.
Not all genes are necessary all the time
Cells must then have the ability to turn a gene on and off
ENTER:  THE OPERON MODEL 
OF GENE EXPRESSION

3. Francois Jacob and Jacques Monod
Experiments with E. Coli showed that it is capable of regulating the expression of its genes
An operon consists of the following elements
1.  Promoter   -  where RNA polymerase attaches, signalling the start of the gene
2.  Operator  -  where a repressor binds, stopping the transcription of that gene
3.  Structural Genes - genes coding for the enzyme, they are transcribed as a unit

4. The trp Operon
It exists in the "on" state and controls the production of tryptophan.
If tryptophan is already present, it binds to the repressor and prevents more tryptophan from being made

6. The lac Operon
This region is normally in the "off" position, it turns on when lactose is present

8. Repressors versus Inducers
The tryp operon is a repressible operon, it is normally on but can be turned off when tyrptophan is present
The lac operon is an inducible operon because it is normally off but can be turned on when lactose is present
Grammar Time
A woman is pregnant and the baby is later.  The doctor says they will "INDUCE" labor tomorrow.  What does he mean?

9. What does this shirt mean?

11. Tying it All Together: Lac Operon

12. In eukaryotes, a variety of mechanisms regulate gene expression
1.  chromatin structure
2.  transcriptional control 3. post transcriptional control
4.  translational control
5.  post translational control

13. Chromatin Structure
DNA is wound around a core of eight protein molecules, the result resembles beads on a string. The protein molecules are histones and each individual bead is called a nucleosome

14. BARR BODIES
In females, chromatin of one of the X chromosomes inactivates, this inactive chromosome is called a BARR BODY
Evidence for barr bodies
1.  Women who are heterozygous for duchenne muscular dystrophy have patches of muscle tissue that are degenerative
2.  Women who are heterozygous for a condition that causes no sweat glands have patches of skin that are normal, and patches that lack sweat glands

15. Barr Body in Cats

16. Genotype:     XB XO
The black patches are XB and the orange patches are XO, the cat is multicolored because not all X's are activated

17. Gene Mutations
Point Mutations - single base changes, causing a change in the amino acid structure (protein)

18. Frameshift mutation
A base is added or deleted and changes the reading frame
G A T    C A T    A A A 
G A T    A  C A   T A A  A

19. What happens when you have a nonfunctional protein?
Hemophilia
PKU
Cystic Fibrosis
Androgen Insensitivity - caused by a faulty receptor for androgens, individual is a chromosomal male but appears female  (hermaphrodite)

20. Cancer and Genetics
Growth of cancer often begins with the loss of the TUMOR SUPPRESSOR GENE 
ONCOGENES activate, cell division occurs uncontrollably
Breast Cancer Gene
BRCA1  (brak-uh)

21. Transposons
Barbara McClintock studying maize corn found that controlling elements could move from one location to another on a chromosome
   --  Transposons or Jumping Genes

22. In maize corn a colorless kernel results from the inability to create purple pigment.
If the transposon jumps to another location, the cells regain the ability to make the pigment, this creates a speckled pattern on the kernel

23. Introns or Exons
Exons = parts of DNA that are transcribed and code for a protein
Introns = sections of DNA that are not transcribed, function unknown
sometimes once called this "JUNK DNA" - scientists now believe this is not accurate

24. What is Epigenetics? See this article from Learn.Genetics
Video at Nova narrated by Neil DeGrasse Tyspon