Chapter 13 Regulation of Gene Activity. 1. “Junk DNA” answer questions in your QOD notebook.

Chapter 13 Regulation of Gene Activity

1. Junk DNA answer questions in your QOD notebook

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/stude nt_view0/chapter13/the_lac_op eron__induction_.html http://highered.mcgraw-hill.com/olc/dl/120080/bio27.swf

http://youtube.com/v/3S3ZOmleAj0http://youtube.com/v/3S3ZOmleAj0 + 3 min to end

Tying it All Together: Lac Operon http://youtube.com/v/ea35iuUT5C8

QOD question: 1. All cells contain a complete copy of DNA (to start), so what make one cell different form another? 2.

Stem Cells: undifferentiated cells One 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

Barr Body in Cats

Genotype: X B X O The black patches are X B and the orange patches are X O, 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.GeneticsLearn.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

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)

Spontaneous vs Induced mutation Occur on their own: vs. due to expose to mutagens Spontaneous often have an unknown background, may be genetic Mutagens: -Physical agents: X-rays, UV-rays, , and -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 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 (hermaphrodite) 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/jamilcolumn 1.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)

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- dont code for proteins, but can still be important to life functions, regulation, structures, features http://www.youtube.com/watch?v=atMVlpNaq40

Chapter 13 Regulation of Gene Activity. 1. “Junk DNA” answer questions in your QOD notebook.

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Transcript of Chapter 13 Regulation of Gene Activity. 1. “Junk DNA” answer questions in your QOD notebook.