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Lecture 12

Lecture 12.docx

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Western University
Biology 1002B
Denis Maxwell

Lecture 12: Prokaryotic Gene Function 1. Identify the sequence of standard "start" and "stop" codons  Start: nontemplate 5’ AUG 3’; template 3’ TAC 5’ (RNA understood)  Stop: non template 5’ UAA, UAG, UGA 3’; template 3’ ATT, ATC, ACT 5’ Eukaryotic Gene Expression Prokaryotic Gene Expression  More genes  Less genes  Genes more spread out on many chromosomes  Genes located on one chromosome  Groups of genes producing proteins with related  Groups of genes producing proteins with related functions are NOT organized into operons functions are organized into operons  mRNA that must have its introns excised  Lack introns  mRNA kept away from ribosomes  Transcription and translation can occur  mRNA transported out of nucleus to ribosomes simultaneously since ribosomes are readily there  5’ cap, poly-A tail added before going to  mRNA doesn’t have a nucleus or nuclear membrane protecting genes (but not floating) translation (post translational)  mRNA tends to be stable, used multiple times  mRNA of prokaryotes is unstable, allow creation  Efficient, but prevents eukaryotes to make fast of new mRNA, which has more opportunities to response changes to environmental disruptions adjust for changing environmental conditions  Synthesis of protein is normally off until activaed Allow for continual synthesis of protein to occur  Gene-regulating before & after transcription in nucleus, in cytoplasm before & after translation 2. DNA sequence “signals” as promoter, 5’ & 3’ UTR, SD box, start & stop codon, transcription terminator etc.  Promoters attract the attention of RNA polymerase o RNA polymerase and DNA interaction create bubble o -10 sequence upstream from start point (+1), TATA promoter (euk promoter is -35) o Start point – where transcription begins reading template strand and is downstream of bubble o Change coding strand to be called non template o 3’ end = downstream; 5’ end = upstream  -35 bases upstream (TTGACA)  Black arrows = where polymerase touches DNA  Green/purple = sites of mutations affect promoter efficiency  Start codon o Signal for translation not transcription o Universal genetic code (same in pro and euks) o Not necessarily the first 3 bases because lots of UTR  terminator is after/downstream stop codon o gets transcribed from DNA into RNA (signal in DNA but understood in RNA) o makes hair pin structure by pairing with itself to signal polymerase to stop  translation initiation is stabilized by mRNA/rRNA base pairing o 5’ UTR (untranslated region since upstream of mRNA start codon) but transcribed  UTR in ribosome is facing up and pair with rRNA since no tRNA will pair with them  rRNA SD box (DNA transcribed, understood in mRNA) pair with UTR (mRNA)  SD box helps initiating translation in bacteria  SD box is an example o
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