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Lecture 12

Lecture 12 Gene Structure and Expression.docx

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Western University
Biology 1002B
Tom Haffie

Lecture 12: Gene Structure and Expression Monday, March 04, 2013 3:35 PM Today's Topics:  Diverse types of signals in DNA  The role of complementary base pairing  Differences between euks and proks  The role of RNA  So what? Announcements:  Homework: Lecture Topic:  Promoters attract the attention of RNA pol which interacts with the DNA  -10 TATA, -35, these sequences from the start point: the location where reading of the gene begins  The startpoint is just downstream of the bubble  The black arrows indicate locations where RNA pol actually touches the DNA  Some promoters are very attractive and very efficient at transcription, but some are not so attractive and not so efficient at transcription  Promoters can be variable  How does transcription in bacteria terminate?  Complementary base pairing occurring between the mRNA being produced and the template DNA  There is a "terminator sequence" in the DNA down stream of the bubble which is transcribed into the mRNA strand produced  It makes a hairpin structure and pairs with itself to make a loop which  The formation of the loop destabilizes the mRNA that is basepaired with the template DNA strand causing it to fall off and signals the polymerase to stop  Some signals (like the terminator) are in the DNA but not understood by the DNA, but rather by RNA or RNA polymerase  Suppose a terminator stops transcription 60% of the time, and another terminator stops transcription 40% of time, how might the two terminators be different?  Maybe the high efficiency terminator is longer and makes the hairpin more stable  Maybe the high efficiency terminator codes for G and C bases which make 3 H-bonds which is stronger than just 2 and this would make the loop more stable  Bacterial transcription terminated by a hairpin loop  For a given chromosome, there is no strand that is the template strand all the time  It depends on where the promoter is  The region between the promoter and the start codon that gets coded into the mRNA is called the 5` UTR (untranslated region)  Ribosomes have two subunits, each containing rRNA and proteins  Translation initiation is st
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