1. What is the Central Dogma? 2. How does prokaryotic DNA compare to eukaryotic DNA? 3. How is DNA organized in eukaryotic cells?

1. Draw and label the 3 parts of an operon. 2. Contrast inducible vs. repressible operons. 3. How does DNA methylation and histone acetylation affect gene expression?

1. List and describe the 3 processes that are involved in transforming a zygote. 2. Compare oncogenes, proto-oncogenes, and tumor suppresor genes. 3. What are the roles of the ras gene and the p53 gene?

Chapter 18

Transcription

 Bacteria need to respond quickly to changes in their environment ◦ if they have enough of a product, need to stop production  why? waste of energy to produce more  how? stop production of enzymes for synthesis ◦ if they find new food/energy source, need to utilize it quickly  why? metabolism, growth, reproduction  how? start production of enzymes for digestion STOP GO

 Feedback inhibition ◦ product acts as an allosteric inhibitor of 1 st enzyme in tryptophan pathway ◦ but this is wasteful production of enzymes = inhibition - -

 Gene regulation ◦ instead of blocking enzyme function, block transcription of genes for all enzymes in tryptophan pathway  saves energy by not wasting it on unnecessary protein synthesis = inhibition - - -

 Cells vary amount of specific enzymes by regulating gene transcription ◦ turn genes on or turn genes off  turn genes OFF example if bacterium has enough tryptophan then it doesn’t need to make enzymes used to build tryptophan  turn genes ON example if bacterium encounters new sugar (energy source), like lactose, then it needs to start making enzymes used to digest lactose STOP GO

Operon Operon: cluster of related genes with on/off switch Three Parts: 1.Promoter – where RNA polymerase attaches 2.Operator – “on/off”, controls access of RNA poly 3.Genes – code for related enzymes in a pathway

operatorpromoter DNATATA RNA polymerase repressor = repressor protein Operon: Promoter, Operator & Genes they control serve as a model for gene regulation gene1gene2gene3gene4 RNA polymerase Repressor protein turns off gene by blocking RNA polymerase binding site mRNA enzyme1enzyme2enzyme3enzyme4

 Repressor protein ◦ binds to DNA at operator site ◦ blocking RNA polymerase ◦ blocks transcription ◦ Produced by regulatory gene

Regulatory generepressor Regulatory gene: produces repressor protein that binds to operator to block RNA poly

 Normally ON  Anabolic (build organic molecules)  Organic molecule product acts as corepressor  binds to repressor to activate it  Operon is turned OFF trp (tryptophan) operon  Eg. trp (tryptophan) operon

mRNA enzyme1enzyme2enzyme3enzyme4 operatorpromoter DNATATA RNA polymerase tryptophan repressor repressor protein repressor tryptophan – repressor protein complex Synthesis pathway model When excess tryptophan is present, it binds to trp repressor protein & triggers repressor to bind to DNA ◦ blocks (represses) transcription gene1gene2gene3gene4 conformational change in repressor protein! 1234 repressor trp RNA polymerase trp

What happens when tryptophan is present? Don’t need to make tryptophan-building enzymes Tryptophan is allosteric regulator of repressor protein

trp operon

 Normally OFF  Catabolic (break down food for energy) inducer  Repressor is active  inducer binds to and inactivates repressor  Operon is turned ON lac operon  Eg. lac operon

mRNA enzyme1enzyme2enzyme3enzyme4 operatorpromoter DNATATA RNA polymerase repressor repressor protein repressor lactose – repressor protein complex lactose lac repressor gene1gene2gene3gene4 Digestive pathway model When lactose is present, binds to lac repressor protein & triggers repressor to release DNA ◦ induces transcription RNA polymerase 1234 lac conformational change in repressor protein! lac

What happens when lactose is present? Need to make lactose-digesting enzymes Lactose is allosteric regulator of repressor protein

lac operon

 Repressible operon ◦ usually functions in anabolic pathways  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 to do, cell allocates resources to other uses

Many stages

 Typical human cell: only 20% of genes expressed at any given time  Different cell types (with identical genomes) turn on different genes to carry out specific functions differential gene expression  Differences between cell types is due to differential gene expression

Chromatin Structure:  Tightly bound DNA less accessible for transcription  DNA methylation: methyl groups added to DNA; tightly packed;  transcription  Histone acetylation: acetyl groups added to histones; loosened;  transcription

 Modifications on chromatin can be passed on to future generations  Unlike DNA mutations, these changes to chromatin can be reversed (de-methylation of DNA)  Explains differences between identical twins

Transcription Initiation:  Control elements bind transcription factors  Enhances gene expression

Enhancer promoter activators Enhancer regions bound to promoter region by activators

Regulation of mRNA: micro RNAs (miRNAs) small interfering RNAs (siRNAs) micro RNAs (miRNAs) and small interfering RNAs (siRNAs) can bind to mRNA and degrade it or block translation

Section 18.4

1. Cell Division: large # identical cells through mitosis 2. Cell Differentiation: cells become specialized in structure & function 3. Morphogenesis: “creation of form” – organism’s shape

 Cytoplasmic determinants: maternal substances in egg distributed unevenly in early cells of embryo

 Induction: cells triggered to differentiate  Cell-Cell Signals: molecules produced by one cell influences neighboring cells ◦ Eg. Growth factors

Section 18.5

1. Proto-oncogene = stimulates cell division 2. Tumor-suppressor gene = inhibits cell division  Mutations in these genes can lead to cancer

Proto-OncogeneOncogene  Gene that stimulates normal cell growth & division  Mutation in proto- oncogene  Cancer-causing gene Effects:  Increase product of proto-oncogene  Increase activity of each protein molecule produced by gene

 Ras gene: stimulates cell cycle (proto- oncogene) ◦ Mutations of ras occurs in 30% of cancers  p53 gene: tumor-suppresor gene ◦ Functions: halt cell cycle for DNA repair, turn on DNA repair, activate apoptosis (cell death) ◦ Mutations of p53 in 50+% of cancers

 Cancer results when mutations accumulate (5- 7 changes in DNA)  Active oncogenes + loss of tumor-suppressor genes  The longer we live, the more likely that cancer might develop

 Embryonic development occurs when gene regulation proceeds correctly  Cancer occurs when gene regulation goes awry