Chapter 13 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 Operon System: genetic regulatory system found in bacteria and their viruses that allows protein synthesis to be controlled and coordinated in response to the needs of the cell

Basically - Gene control system in bacteria and viruses

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, signaling 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

Repressor: protein that inhibits expression of a gene

Repressors versus Inducers

repressor operon: turns transcription OFF it is normally on but can be turned off when tyrptophan is present ex: Tryp operon inducer operon: turns transcription ON is normally off but can be turned on when lactose is present ex: lac operon

Grammar Time A woman is pregnant and the baby is late. The doctor says they will "INDUCE" labor tomorrow. What does he mean?

http://highered.mcgraw-hill.com/sites/0072556781/student_view0/chapter12/animation_quiz_3.html

What does this shirt mean?

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 turns off- prevents more tryptophan from being made

lac Operon This region is normally in the "off" position, it turns on when lactose is present (low glucose)

http://highered.mcgraw-hill.com/sites/007352543x/student_view0/chapter13/the_lac_operon__induction_.html

http://highered.mcgraw-hill.com/olc/dl/120080/bio27.swf

http://youtube.com/v/3S3ZOmleAj0 + 3 min to end

https://www.youtube.com/watch?v=3S3ZOmleAj0

Tying it All Together: Lac Operon

http://youtube.com/v/ea35iuUT5C8

(NOT a QOD, just think about and do) 1. All cells contain a complete copy of DNA (to start), so what make one cell different form another? 2. Explain the operon you colored to your table partner, do you understand the operon that you did NOT color (lac or tryp)

Stem Cells: undifferentiated cells

Once cells differentiated, certain parts of the DNA are “turned off” depending on the cell function.

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

1. 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

Chromatin continued… Heterochromatin: tightly coiled, inaccessible to RNA polymerase (barr bodies) Euchromatin: loosely packed, associated with active genes

-access regulated by histones

http://www.youtube.com/watch?v=29doT6Hf2MI

http://www.youtube.com/watch?v=kZXKNYSXBCs

BARR BODIES: inactive X chromosome in a female somatic cell

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

Big Question 1: Why are there no male calico cats?

Case Study - Calico Cats Chromosomes & Inheritance

Big Question 2: Why do CC and Rainbow not look exactly alike, even though they are clones?

CC (Carbon Copy) Rainbow

Genes are found on chromosomes, in most cases, you receive 2 alleles.

Shown is a human karyotype which contains 22 pairs of autosomes 1 pair of sex chromosomes

1. When would a person only have 1 allele for a trait?

Cat Karyotype 2. How is it similar to the human karyotype? How is it different?

The genes for coat color in cats are located on the X chromosome.

Alleles can be: Orange or Black

Alleles are codominant

3. What is Spaz’s genotype?

There are some rare cases of male calico cats. Weird!

During meiosis, each egg and sperm should receive only one copy of each chromosome (haploid) 4. Examine the graphic, describe (in words) what nondisjunction is.

8. What do male calico cats, children with Down syndrome and children with Turner syndrome all have in common?

Big Question 2: Why do CC and Rainbow look different even though they are clones?

Consider how color is expressed on a calico cat.

Some areas express orange, some black…. It seems oddly random.

A Barr body (named after discoverer Murray Barr) is the inactive X chromosome in a female somatic cell, rendered inactive in a process called lyonization, in those species in which sex is determined by the presence of the Y

10. How do Barr Bodies explain CC and Rainbow?

CC (Carbon Copy) Rainbow

Barr Body in Cats

11. Consider a male calico cat. Do you think this calico would have cognitive disabilities similar to those found in children with Down Syndrome. Why or Why not?

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

Methylation: addition of a methyl group (to DNA) that alter the expression of genes- turning them off

What is Epigenetics?

See this article from Learn.Genetics Video at Nova narrated by Neil DeGrasse Tyspon 3:35

When pattern of inheritance does not depend on genes (environmental influences)

http://learn.genetics.utah.edu/content/epigenetics/intro/

http://www.pbs.org/wgbh/nova/body/epigenetics.html

2. Transcriptional control -  Transcription can be

promoted or repressed: -  Need the correct

combination of transcription factors, proteins that regulate transcription, to start gene transcription

-  Transcription activator: Bind to promoter and increase gene transcription

3. Posttranscriptional Control §  Occurs in nucleus §  Includes alternative mRNA splicing

- pre-mRNA introns removed

4. Translational Control

-  Occurs in cytoplasm -  Certain microRNAs present

in the cytoplasm can affect the 5’ cap or ploy-A tail at the 3’ end and alter translation

5. Posttranslational Control

- Protein synthesis and activation (folding)

Summary: gene control/ regulation Prokaryotic: Operon system (lac and tryp operon) Eukaryotic: 1. chromatin structure: histones:

Heterochromatin (bar bodies) and Euchromatin, methylation,

2. transcriptional control: transcription factors, activator, promotor 3. post transcriptional control: rna splicing 4. translational control: cap or tail (delay translation) 5. post translational control: folding

What are the types of mutations?

(just think about it, this is not a QOD)

Spontaneous vs Induced mutation Occur “on their own”: vs. due to exposure to mutagens Spontaneous often have an unknown background, may be genetic Mutagens:

-Physical agents: X-rays, UV-rays, α, β and γ-rays. -Chemical agents: Mustard gas, Ethylene amine, Colchicine, Ethyl-methyl sulphonate(EMS)

Gene Mutations

Point Mutation - substitute one base for another Original: A T A C A C Mutant : T T A C A C Frameshift Mutation - a base is either added or removed which causes a shift in the reading frame. Many genes affected

- include insertion and deletion Original: A T A C A C A A G C C A Mutant: A T T A C A C A A G C C A

Silent Mutation - a base is changed but the resulting amino acid is the same as in the non mutant DNA. No outward changes. Original: A A A C A G Mutant: A A G C A G Nonsense Mutation - a codon is changed to a STOP codon Original: A T A C C C A A A Mutant: A T T C C C A A A

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 (pseudohermaphrodite)

Do you watch House?

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

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

DNA and RNA transposons move around the genome. DNA transposons cut themselves out from their original location, and insert themselves somewhere else in the genome. RNA transposons make a copy of themselves that inserts into a new location, leaving the original transposon intact. (may have originated from viruses)

Transposons

1.  Define Transposons (there are 2+ types) 2.  What effects do they have? Give an example. 3.  What else did your learn from this article?

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)

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 Junk DNA?

Face is junk DNA http://www.youtube.com/watch?v=gQGGg6lADhE

•  Use to be considered useless

•  Now, it is considered “noncoding”- don’t code for proteins, but can still be important to life functions, regulation, structures, features

http://www.youtube.com/watch?v=atMVlpNaq40