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Lecture 14

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Biology 1002B
Denis Maxwell

Lecture 14: Eukaryotic Gene Expression 1. Basic structure of eukaryotic vs prokaryotic cell with respect to gene expression  Prokaryotic: DNA  transcription  mRNA  translation  ribosome  Eukaryotic: DNA  transcription  premRNA (endomembrane advantage) translation  ribosome o Promoter proximal region is upstream of promoter o Protein binding sites near promoter o Slash – long distance o Regulation and alternative splicing o Translation & transcription not simultaneous since nucleus keeps RNA away from ribosomes 2. Protein motifs common in DNA binding proteins in eukaryotes to affect regulation  TATA box in AT rich region in promoter promotes DNA strands to unwind  Have right protein shapes to bind (proteins charged in specific areas)  Helix-turn-helix DNA binding motif e.g. lac repressor o The part that actually grabs on the DNA is the helix turn o Not making covalent bonds but electrostatic attraction  Zinc finger DNA binding motif binds the major groove o Particular amino acid make particular helix shape o Associate with zinc cofactors  Leucine zipper hold 2 monomeric DNA binding proteins together in shape o Protein binding proteins are often dimers, work in pairs  Motives are an indicator of transcription regulator or DNA binding protein 3. Mechanism of transcription and its termination in euks  Determines which genes are transcribed  Regulate efficiency of polymerase binding  Promoters and enhancers regulate transcription  Promoters o TATA binding protein (TBP) make promoter attractive to polymerase II o Proteins, transcription factors pile downstream to max attraction o Positioned dependent – will not get transcribed if far away o Direction dependent – inverted: wrong transcription direction  Enhancers o Not positioned dependent – bend, trap whole initiation complex  Attractive promoter with loop (↑ transcription) o Direction independent since they can bend and twist  Crossover during meiosis, swap but not separate enhancers  Virus with mega enhancer – gene will be overexpressed  Silencers (opp of enhancers) stop transcription by stabilizing negative activator proteins  Polyadenylation signal (Don’t have terminator loops in eukaryotes) o Polymerase transcribes through polyadenylation signal recognized in mRNA by an RNAse o RNAse cuts message off to tell it to stop and add tail o Poly – A polymerase adds poly tail of A’s (no T’s) at 3’; not complementary base pairing o no DNA signal for the G cap that is added on 5’ 4. Removing introns (see diagram on next page)  snRNA (small nuclear RNA) – all RNAs pair with themselves  Intron after transcription attract reused snRNP (snRNA + protein)  Either intron end signal spliceosome (several snRNP) where to cut introns by snRNA pairing with message o DNA signals translated into mRNA so snRNPs understands 5. Mechanism of transla
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