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Lecture 14

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Western University
Biology 1002B
Tom Haffie

Lecture 14: Eukaryotic Genes Although many aspects of eukaryotic gene structure and expression are similar to that in bacteria, the compartmentalization of eukaryotic cells affords dramatically increased opportunities for regulation.  basic structure of eukaryotic vs prokaryotic cell with respect to gene expression - Ribosomes are kept away from mRNA in euks - There are different levels of regulation.  structure of eukaryotic endomembrane system with respect to gene expression  structure of eukaryotic promoters/enhancers - More than one RNA polymerase – polymerase 2 does not bind to “naked” promoters o Polymerase 2 recognizes protein coding promoters o Polymerase 2 only finds promoters attractive if proteins (TATA binding protein) are already bound to promoters o TATA box – sequence found in promoter region that is important in determining the position where transcription is initiated. o Naked (no protein) promoters are not attractive to polymerase 2  protein motifs common in DNA binding proteins Transcription factors regulate efficiency of polymerase binding - How do proteins bind DNA? Electrostatic – DNA (-) proteins (+) - Proteins must be particular shape to fit into helix o Helix turn helix  Lac repressor has helix turn helix protein for binding onto operator region of lac. o Zinc finger DNA binding motif binds with the major groove  Series of amino acids that are able to associate with zinc cofactors and form a specific shape that recognizes DNA sequence  Codes for DNA binding protein o Leucine zipper holds two monomer DNA binding proteins together  DNA binding proteins often acts as dimers  Zipper holds them together  Contains zipper = coding for DNA binding protein  mechanism of transcription termination in euks  mechanism of translation initiation in euks  which gene expression components cross the nuclear membrane to get from where they are made to where they function  various stages of gene expression subject to regulation Enhancer can be far away or close to gene because folding will stabilize - Promoters are position dependent and have direction where enhancers do not. If you invert promoter polymerase would be sent the other way. One way to get different expression of different genes. - Regulating enhancers - Regulating attractiveness of promoters by binding proteins onto them Message is transcribed – how transcription stops in euks – transcription termination - on 5’ end there is a cap - Other end is polyadenylation signal o Polymerase transcribes through signals – recognized by mRNA - RNA cuts that off and
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