Lecture 037 - Eukaryotic Genetics

1 Colonie High AP Biology DeMarco/Goldberg The BIG Questions . Chapter 16 How are genes turned on & off? How do cells with the same genes Regulation of Gene differentiate to perform completely different, Expression specialized functions in multicellular eukaryotes? Bacterial Metabolism Reminder: Regulation of Metabolism Bacteria need to respond quickly to Feedback inhibition changes in their environment product acts ex. if have enough of a product, as an allosteric need to stop production inhibitor of why? waste of energy to produce more 1st enzyme in how? stop production of synthesis enzymes tryptophan ex. if find new food/energy source, pathway need to utilize it quickly why? metabolism, growth, reproduction how? start production of digestive enzymes - = inhibition Another Way to Regulate Metabolism Gene Regulation in Bacteria Gene regulation Control of gene expression enables block individual bacteria to adjust their transcription of metabolism to environmental change genes for all enzymes in Cells vary amount of specific enzymes tryptophan by regulating gene transcription pathway turn genes on or turn genes off saves energy by ex.

2 If you have enough tryptophan in your not wasting it on cell then you don't need to make enzymes unnecessary protein used to build tryptophan synthesis waste of energy! turn off genes which codes for enzymes - = inhibition Colonie High AP Biology DeMarco/Goldberg Genes Grouped Together So how can genes be turned off? Operon First step in protein production? genes grouped together with related functions transcription ex. enzymes in a synthesis pathway promoter = RNA polymerase binding site stop RNA polymerase! single promoter controls transcription of all Repressor protein genes in operon transcribed as 1 unit & a single mRNA is made binds to DNA near promoter region operator = DNA binding site of regulator protein blocking RNA polymerase binds to operator site on DNA. blocks transcription Repressor Protein Model Repressible Operon: Tryptophan Synthesis Pathway Model Operon: When excess tryptophan is present, RNA The operator, promoter & genes they control RNA binds to tryp repressor protein &.

3 Polymerase polymerase serve as a model for gene regulation triggers repressor to bind to DNA. (blocks [represses] transcription). RNA RNA. TATA repressor polymerase gene1 gene2 gene3 gene4 DNA TATA repressor polymerase gene1 gene2 gene3 gene4 DNA. repressor repressor protein Repressor protein turns off gene by promoter operator blocking RNA polymerase binding site. promoter operator tryptophan (a corepressor). tryptophan repressor protein repressor repressor repressor protein complex conformational change in repressor protein! Tryptophan Operon Inducible Operon: Lactose What happens when tryptophan is present? Digestive pathway model Don't need to make tryptophan-building enzymes! RNA. When lactose is present, binds to lac repressor protein & triggers polymerase repressor to release DNA. (induces transcription). RNA. TATA repressor polymerase gene1 gene2 gene3 gene4 DNA. repressor repressor protein promoter operator lactose lactose repressor protein repressor complex conformational change in Tryptophan binds allosterically to regulatory protein.

4 Repressor protein! Colonie High AP Biology DeMarco/Goldberg Lactose Operon Operon Summary What happens when glucose is not available Repressible operon and lactose is present? usually functions in anabolic pathways Need to make lactose-digesting enzymes! synthesizing end products when end product is present in excess, cell allocates resources to other uses Inducible operon usually functions in catabolic pathways digesting nutrients to simpler molecules produce enzymes only when nutrient is available cell avoids making proteins that have nothing Lactose binds allosterically to regulatory protein. to do, cell allocates resources to other uses 1961 | 1965. Jacob & Monod: lac Operon Transcription Another Look . Francois Jacob & Jacques Monod The process of transcription includes first to describe operon system many points of control coined the phrase operon when to start reading DNA. where to start reading DNA. where to stop reading DNA.

5 Editing the mRNA. protecting mRNA as it travels through cell Jacques Monod Francois Jacob 1990s | 2006. Eukaryotic Transcription Transcription Roger Kornberg Initiation complex for his studies of the molecular basis of transcription factors bind to promoter Eukaryotic transcription region upstream of gene proteins which bind to DNA & turn on or off transcription TATA box binding site only then does RNA. polymerase bind to DNA. Roger Kornberg Colonie High AP Biology DeMarco/Goldberg Transcription Transcription Initiation Promoter sequences upstream of gene Control regions on DNA. promoter nearby control sequence on DNA. binding of RNA polymerase & transcription factors base rate of transcription enhancers distant control sequences on DNA. binding of activator proteins enhanced rate (high level). RNA polymerase of transcription molecules bound to bacterial DNA. Model for Enhancer Action Transcription in Eukaryotes Enhancer DNA sequences distant control sequences Activator proteins bind to enhancer sequence & stimulates transcription Silencer proteins bind to enhancer sequence & block gene transcription Prokaryote vs.

6 Eukaryote Genome Prokaryote vs. Eukaryote Genome Prokaryotes Eukaryotes small size of genome much greater size of genome how does all that DNA fit into nucleus? circular molecule of naked DNA DNA packaged in chromatin fibers DNA is readily available to RNA polymerase how to regulate access to DNA by RNA polymerase? control of transcription by regulatory proteins cell specialization operon system need to turn on & off large numbers of genes most of DNA codes for protein or RNA most of DNA does not code for protein no introns, small amount of non-coding DNA 97% junk DNA in humans; purpose? regulatory sequences: promoters, operators Colonie High AP Biology DeMarco/Goldberg Hepatitis Viral Gene Expression Viral Diseases influenza bacteriophage Polio A package of genes in transit from one host cell to another Measles A piece of bad news wrapped in protein . Peter Medawar Chicken pox Smallpox Emerging Viruses Eradicated in 1976 Viruses that jump host switch species vaccinations ceased in 1980.

7 Ebola, SARS, bird flu, at risk population? hantavirus The Coming Plague by Laurie Garrett SARS. Ebola hantavirus A Sense of Size What is a virus? Is it alive? Comparing size DNA or RNA enclosed in a protein coat Eukaryotic cell Viruses are not cells bacterium Extremely tiny virus need an electron microscope to see smaller than ribosomes ~20 50 nm 1st discovered in plants (1800s). tobacco mosaic virus couldn't filter out couldn't reproduce on media like bacteria Colonie High AP Biology DeMarco/Goldberg Variation in Viruses Viral Genomes plant virus pink eye Parasites? Viral nucleic acids lack enzymes for DNA. metabolism double-stranded lack ribosomes for single-stranded protein synthesis RNA. need host double-stranded machinery single-stranded Linear or circular smallest viruses have only 4 genes, while largest have several hundred Viral Protein Coat Viral Envelope Capsid Lipid bilayer membranes crystal-like cloaking viral capsid protein shell envelopes are derived from 1-2 types of host cell membrane proteins glycoproteins on surface many copies of same protein HIV.

8 Generalized Viral Lifecycle Symptoms of Viral Infection Entry Link between infection & symptoms varies virus DNA/RNA enters host kills cells by lysis cell cause infected cell to produce toxins Assimilation fever, aches, bleeding . viral DNA/RNA takes over host viral components may be toxic reprograms host cell to copy envelope proteins viral nucleic acid & build viral proteins Damage? Self assembly depends . nucleic acid molecules & lung epithelium after the flu is repaired capsomeres then self- nerve cell damage from polio is permanent assemble into viral particles exit cell Colonie High AP Biology DeMarco/Goldberg Viral Hosts Bacteriophages Host range Viruses that infect bacteria most types of virus can infect & parasitize ex. phages that infect E. coli only a limited range of host cells lambda (l) phage . identify host cells via lock & key fit 20-sided capsid head between proteins on viral coat & encloses DNA. receptors on host cell surface protein tail attaches broad host range phage to host & injects rabies = can infect all mammals phage DNA inside narrow host range human cold virus = only cells lining upper respiratory tract of humans HIV = binds only to specific white blood cells Bacteriophage Lifecycles Lytic Lifecycle of Phages Lytic reproduce virus in bacteria release virus by rupturing bacterial host Lysogenic integrate viral DNA.

9 Into bacterial DNA. reproduce with bacteria Lysogenic Lifecycle of Phages Defense Against Viruses Bacteria have defenses against phages bacterial mutants with receptors that are no longer recognized by a phage natural selection favors these mutants bacteria produce restriction enzymes recognize & cut up foreign DNA. It's an escalating war! natural selection favors phage mutants resistant to bacterial defenses Colonie High AP Biology DeMarco/Goldberg RNA Viruses Retroviruses Retroviruses HIV. have to copy viral RNA into host DNA Human ImmunoDeficiency Virus enzyme = reverse transcriptase causes AIDS. RNA DNA mRNA Acquired ImmunoDeficiency host's RNA polymerase now transcribes Syndrome viral DNA into viral mRNA opportunistic diseases mRNA codes for viral components envelope with host's ribosomes produce new viral proteins glycoproteins transcription translation for binding to DNA RNA protein specific WBC. capsid containing 2 RNA.

10 Replication strands & 2 copies of reverse transcriptase HIV Infection HIV Treatments HIV enters host cell inhibit vRNA replication macrophage & CD4 WBCs AZT. cell-surface receptor thymine mimic reverse transcriptase protease inhibitors synthesizes double stranded DNA from viral RNA stops cleavage of polyprotein into high mutation rate capsid & enzyme proteins Transcription produces more copies of viral RNA. translated into viral proteins proteins & vRNA self- assemble into virus particles released from cell by budding or by lysis Potential HIV treatments HIV Treatments Block receptors inhibit vRNA replication chemokines AZT. bind to & block cell-surface receptors thymine mimic 11% of Caucasians have mutant receptor allele Block vRNA replication protease inhibitors CAF replication factor stops cleavage of polyprotein into capsid & enzyme proteins Colonie High AP Biology DeMarco/Goldberg Why turn genes on & off? Points of Control Specialization The control of gene expression can occur at any step in the each cell of a multicellular eukaryote pathway from gene to functional expresses only a small fraction of its genes protein Development unpacking DNA.