Chapter 15 Regulation of Gene Activity

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

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

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

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

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?

What does this shirt mean?

Tying it All Together: Lac Operon

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

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

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

Barr Body in Cats

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

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

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

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)

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)

Transposons http://www.thenakedscientists.com/HTML/articles/article/jamilcolumn1.htm/ Barbara McClintock studying maize corn found that controlling elements could move from one location to another on a chromosome    --  Transposons or Jumping Genes

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

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

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