Gene Regulation in Eukaryotes modulating the amount of gene product o Different from prokaryote gene regulation Occurs in the nucleus Large amounts of non coding DNA Uncoupled transcription and translation Monocystronic Introns and exons possible than in polycistronic RNA modification Multicellularity Chromatin o Types of regulation 1 Transcriptional control During initiation phase each gene is individually regulated more combination of genes o Access to promoter by chromatin modification Chemical modification of histone tails that causes them to be more or less attracted to DNA Acetylation neutralizes charge of histone tails o HAT enzyme histone acetyl transferase binds and neutralizes charge of histone DNA is less packed more transcription causes DNA to be more packed histone deacetylase binds and o HDAC enzyme Phosphorylation Methylation Chromatin remodeling enhancer can bind to TATA box rearrange positioning of nucleosomes so Chromatin remodeling complexes CRCs moves nucleosome or unwinds DNA proteins that o Can slide nucleosome or disassemble nucleosome to expose DNA o Rate of assembly at initiation complex Activator proteins enhancer sequence upstream of promoter gene specific help assemble complex faster bind at Many types of transcription factors more complexity and diversity Insulators prevents activators from interacting with wrong initiation complex triggered by specific DNA sequence protein binds breaks sequence Enhancers cannot act on promoters located in between insulators o Rate of transition to elongation phase Activator proteins also used to help transition to elongation phase DNA loops around activator interacts with the mediator Mediator mediator interacts with Pol II affect Pol II multiprotein complex that integrates signals that Like a switchboard integrates and determines where signals from activators and repressors will go Initiation of elongation phosphorylation of carboxy terminal tail of Pol II CTD protein end of protein that when phosphorylated chemically triggers pol II to begin transcription elongation 2 Post transcriptional control Alternative splicing same pre mRNA is spliced in different ways to produce different mRNAs that are translated into different amino acid sequences done by linking different combinations of exons together o Increases information content o Relative order of genes is not changed but different exons can be chosen to be put together which exons are expressed depends on where the pre mRNA is spliced Activators and repressors regulate splicing o Control splice site recognition by U1 or U2 snRNPS o Ex different splicing for sex in fruit flies Exon 4 in males has a weak 3 splice site spliceosome doesn t recognize so splicing doesn t occur here 3 5 Tra protein in females expressed acts as a splicing activator and exon 4 splice site is used 3 4 5 creates continuous reading frame that can be read by ribosomes Splicing during translation Occurs in the nucleus Introns Exons non coding sequences removed 25 of genome coding sequences expressed o Order of exons is maintained Splice sites ends of exons and introns are marked by specific consensus sequences that are mediated by large ribonucleoprotein complexes lies between 5 and 3 splice sites Branch point Process 1 Cleaved at 5 splice site 2 5 end of intron folds back on itself to form a lariat binds at the branch point 5 phosphate of guanine attaches to 2 OH of adenine 3 Cleaved at 3 splice site intron is released as a lariat and exons are joined together Spliceosome splicing splice site sequences o Ribonucleoprotein large multiprotein complex that is responsible for protein RNA responsible for finding mRNA base pairs are complementary to snRNA in spliceosome o Composed of U1 U2 U3 U4 U5 U6 addition of methylated guanine extra nucleotide at 5 end and 5 cap methyl groups on the base of the nucleotide and the 2 OH group of the sugar o Initiates translation cap bind proteins bind here o Increases stability of mRNA o Influences removal of introns o Only occurs in mRNA transcribed by RNA pol II after cleavage AAA tail is added to 3 end of cleaved mRNA via Poly A tail polyadenylation o Functions Transport recognition sequence for proteins that move sequence into cytoplasm for translation Stability resist degradation so mRNA is available for translation for longer amount of time 3 Translational control Initiating translation and attachment of ribosome Global control all messages in cell are regulated at the same time o Phosphorylation of eIF2 inactivates it no translation because large subunit cannot attach Used to bring tRNA small ribosomal subunit and other initiation factors to mRNA start site mRNA gene specific control steric blockage o Ferritin gene regulation of iron gene specific Low iron RNA forms hairpin structure iron regulatory proteins IRP recognize hairpin and bind ferritin mRNA blocks movement of ribosome down mRNA no translation Presence of iron allosteric change in IRP IRP falls off translation on heritable changes in gene expression not associated with changes in Epigenetics DNA code paternal origin of a chromosome determines the expression Imprinting characteristics of a gene same genotype but different phenotype in progeny o Ex Prader Willi deletion from father or Angelman deletion from mother syndromes Mechanisms o DNA methylation Usually occurs at cytosine Methyltransferase guanine bonds and methylates cytosine recognizes CpG cytosine phosphate Recognizes methylated CpGs and methylates nearby CpGs Methylation patterns are copied and can be inherited via semiconservative model Methylated DNA in promoter no transcription o Chromatin modification see above Implications o Cause of many diseases can change methylation patterns to threat diseases generations o Actions and environments impact gene expression for future o New drug targets creating writers erasers readers that target certain genes in genome RNA based regulation RNA interference intracellular system that recognizes the presence of dsRNA in a cell and triggers the selective degradation of RNAs complementary to the dsRNA immune response 1 Dicer responsive to double stranded RNA like cuts dsRNA into fragments siRNAs Mechanism of dsRNA silencing 2 Fragments associate with RNA induced silencing complexes RISC with help of the argonaute enzyme 3 RISC and argonaute enzyme cleave 1 strand of DNA which is used as guide RNA o Other strand is cleaved passenger strand 4 RISC and guide RNA pair up with target complementary mRNA