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Lecture 13

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Western University
Biology 1002B
Tom Haffie

Lecture 13: Prokaryotic Gene Regulation  Tom’s lectures this term o Availability: Drop in: [email protected] 1 -3, F @ 2-3 pm RM 301G NCB o Appointments also by email o [email protected] o Put “1002B” in subject  Be familiar with chapter 13 and 14  Modern endosymbionts have a “prokaryotic” genetic system o Mitochondrion and chloroplast has “prokaryotic” genetic systems  Different DNA from nucleus (eukaryotic)  Where is the start and ending codons, which way does translation go, where is the promoter, where is the SD box, et c.  A typical prokaryotic gene has many types of signals coded in DNA o The image on the slide  Green part: promoter  Yellow part: SD box  Green: start codon  Red: stop codon  Pink: translation terminator  Which of these signals is transcribed but not translated o Promoters are not transcribed, they attract the polymerase o Start codons are transcribed and translated o Stop codons are transcribed but not translated o Terminator sequences are transcribed but not translated  What if these signals are changed by mutations? o What happens to a mutation in promoter  It depends  The RNA polymerase may not recognize the gene or it can increase its efficiency (positive effect) o What happens to a mutation in SD box  It depends  It may make it more or less functional  Some effect on the efficiency of translation  Unless the mutation makes a start codon o What happens to a mutation in start codon  For start codon, all mutations will break it, probably kills the gene, lethal mutations  Cannot make start codon better because its only AUG o What happens to a mutation in a stop codon  It depends  You can mutate a stop codon into another stop codon  If you turn stop codon into any other codons, then translation will continue until it reaches the next stop codon  We can find redundant stop codons at the end of the gene to secure a fully stop o What happens to a mutation in the terminator  It depends  We can enhance the loop, more efficient or make it worse, less efficient  Remember trp (tryptophan UGG)  Substitution mutation may: o Silent mutation  Mutation that substitute a codon with the different code for the same codon, no effect at all o Missense codon  Creating new codons that wasn’t there before,
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