Chapter 15 Gene Expression [control of kinds and amount of protein produced

15.1 –Control Mechanisms A. Interact with RNA, DNA, New Polypep. or final proteins B. Respond to hormones or changes in concentrations C. Positive control: enhance protein prod. 1. Enhancers = bind to sites on DNA & Increase transcription 2. Acetylation = Acetyl group added to DNA: makes gene accessible by removing histones

D. Negative Control = slow or stop activity – 1. Methylation=methyl group added to DNA blocks gene access

15.1- Control mechanisms work at different points in the protein synthesis process 1. Pre-transcription control A. control access to genes by winding and unwinding DNA [methylation or acetylation] B. multiply gene sequences = polytene chromosomes with many copies of same gene

– 2. transcript processing control A. change how transcript is processed (how exons are connected, in what order) changes how protein functions B. bind proteins to end of mRNA – i. allow transcript to exit nucleus – ii. Direct where in cell mRNA goes C. y-box proteins – i. bind to mRNA: block translation – ii. Allow stockpiling of mRNA – iii. Only phosphorylation activated y-box will work

3) Translation Control A) control how long mRNA lasts (longer = more copies of protien) 1) long poly A tail = last long 2) attached proteins can slow degredation B) block translation 1) proteins bind to mRNA to block translation 2) initiation factors can be inactivated

4) Post-translation control of polypeptide A) some need phosphorylation to activate B) allosteric control ( activators/ inhibitors)

15.1 Cell differentiation – cells become specialized A) transcription controls select subsets of genes to use thereby becoming specialized B) example: Only red blood cells transcribe hemoglobin genes (pg. 233 flow chart)

15.2 Example Gene Control Outcomes A. X-chromosome inactivation 1. one X stays condensed a. 75% genes inactivated b. inactivated X = a Barr body c. inactivation occurs in embryo ball of cells (first few days) d. in each cell either maternal or paternal X inactivates ……its random for each cell what one inactivates

e. descendant cells make same X inactivation as embryonic parent cell i. mosaic tissues form with patches of cells with active maternal x and others with active paternal X ii. Calico cats – black color on one X orange color on the other (pg. 234)

2. Dosage compensation theory a. x-inactivation=gene control mech. b. to balance gene expression between male and female

3. XIST gene a. x-linked gene makes large RNA molecule that sticks to the chromosomal DNA b. only active on one of the x chromosomes c. that x in inactivated B. Another Gene control outcome = ABC model 1. A, B, and C are sets of master genes 2. Different sets and combination of sets give different tissues 3. see ex. pg 235

15.3 Homeotic Genes (Hox genes) A. Master genes – map out body plan 1. control the body plan of embryos by controlling differentiation of groups of cells 2. Homeotic genes include a 180-nucleotide sequence called a homeobox. 3. Homeobox sequence of DNA codes for Homeodomain region of a regulatory protein 4. Homeodomain is the part of the protein that binds to the DNA to regulate transcription (activates or inactivates promoters and/or enhancers) 5. The rest of the protein determines what gene it binds to

B. Different homeotic (master) genes are transcribed in different parts of embryo 1. switch on proper genes for that body part C. Homeotic genes highly conserved 1. identical or very similar in all animals 2. related genes in yeasts, bacteria & plants 3. indicates Homeobox DNA evolved early

15.4 Knockout Experiments A. gene mutated, so no protein B. effect of missing gene is studied C. gives clues as to function of knocked out gene D. genes also engineered to be turned off or on by researcher The 2007 Nobel Prize in Physiology or Medicine goes to M. R. Capecchi, M. J. Evans, and O. Smithies for their discoveries of principles for introducing specific gene modifications in mice by the use of embryonic stem cells.

15.5 Prokaryotic Gene Control example = lac operon A. prokaryotes control transcription (pg. 238) – 1. operons – system where gene or genes are controlled by a promoter and a pair of operators. A. operators = DNA cod acts as binding sites for repressor proteins (regulatory protein) B. when repressor protein bind to operons, genes not transcribed (pg. 239)

– 2. Example: lactose operon (negative control) A. absence (presence of glucose) of lactose: repressor binds to operons=no lactose digesting enzymes B. presence of lactose (and presence of glucose) – i. lactose converted to allolactose – ii. Allolactose binds to repressor protein – iii. Repressor lets go of operons – iv. Lac operon promoter expose and genes transcribed – v. lactose digesting enzymes translated

– 3. Example: lactose operon (positive control) A. absence of glucose allows cAMP (cyclic adenosine monophos.) production. cAMP production is blocked by glycolysis B. cAMP binds to CAP (catabolite activator protein) C. CAP – cAMP complex makes promoter of lactose operon more attractive to RNA polymerase.

– 4. Lactose intolerance A. small intestine makes less lactase B. lactose reaches large intestine undigested C. bacteria digest lactose and make gas and fatty acids (diarrhea)