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Lecture 14

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Western University
Biology 1001A
Tom Haffie

Basic structure of eukaryotic vs prokaryotic cell with respect to gene expression - ● Fundamental difference between eukaryotes and prokaryotes with respect to gene expression is the presence of the nucleus in eukaryotes Structure of eukaryotic endomembrane system with respect to gene expression - ● Structure of eukaryotic promoters/enhancers - ● The promoter proximal regions are protein binding sites near promoter which when bonded with protein cause the promoter to be more attractive to RNApolymerase II ● The Promoter is where the RNApolymerase II binds ● RNApolymerase II only finds promoter attractive if proteins are associated with the promoter which is where TATAbinding proteins come into play ○ TATAbinding protein associate around TATA box making promoter more attractive ● The enhancer can be quite far away from the rest of the sequence ● Protein motifs common in DNAbinding proteins - ● Helix-turn-Helix DNAbinding motif: an alpha helix, then turn, then another alpha helix ○ Lac repressor uses this motif to bind to the operator in lac operons ● Zinc finger DNAbinding motif: series of amino acids that fold around Zn; makes an alpha helix that binds Zn (Zn is a cofactor) ● Leucine zippers: DNAbinding proteins tend to be dimers and leucine zippers hold dimers together so that they can bind to DNA Mechanism of transcription termination in euks - ● Eukaryotes don’t have a loop to terminate transcription, rather use a Polyadenylation signal ● On one end of an RNAtranscript in eukaryotes, you have a 5’cap and on the other end you have a polyadenylation signal ● The signal is first present in DNA; the RNApolymerase II transcribes through it and when it is transcribed, it is recognized by a RNAase (enzyme) that cuts it ● RNA polymerase stops transcribing after message is cut and afterwards, the polyA tail is added Mechanism of translation initiation in euks - ● Translation initiation in eukaryotes is a result of the ribosome recognizing the 5’cap of the mRNA transcript. Once found, the ribosome slides along downstream until the start codon is found and translation can begin ● There is no SD box in eukaryotes! Which gene expression components cross the nuclear membrane to get from where they are made to where they function - ● All proteins must cross through the nuclear membrane as they are transcribed in the nucleus but translated in the cytoplasm ● Certain kinds of RNAalso must cross the nuclear membrane such as mRNA, rRNA, and tRNAbut other RNAsuch as snRNAneed not leave the nucleus as they do their function there as well Various stages of gene expression subject to regulation - ● Transcriptional regulation: Determines which genes are transcribed ○ Regulation of transcription initial ○ Chromatin remodeling to make genes accessible for transcription ● Posttranscriptional regulation: Determines types and availability of mRNAs to ribosomes ○ Variations in pre-mRNAprocessing ○ Removing of masking proteins ○ Variations in rate of mRNAbreakdown ○ RNAinterference ● Translational regulation: Determines rate at which proteins are made ○ Variations in rate of initiation of protein synthesis ● Posttranslational regulation: Determines availability of finished proteins ○ Variations in rate of protein processing ○ Removing of masking segme
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