Essential Elements of Biochemistry BCHM 3050 Dr Srikripa Chandrasekaran Lecture 3 4 15 Notes Transcription I One Gene One Enzyme A In 1941 Beadle and Tatum wanted to find a link between the genetic information and these characteristics B They were chasing after a phenotype enzymes C They were the one to propose that for every gene there is one enzyme we know this to not be true now because one gene can influence many enzymes and one enzyme can influence many genes D We know that many genes can collaborate together many genes control one feature and one gene can control many features 1 Example red hair is usually associated with freckles E They proposed the 1 gene 1 enzyme hypothesis F They used yeast and looked at one specific pathway making an amino acid Arginine they found that it takes 3 main steps they studied the pathway of how yeast make arginine G Enzyme 1 only influenced the making of ornithine Enzyme 2 only influenced the making of citrulline Enzyme 3 only influenced the making of arginine H They took 5 test tubes in which they grew yeast slants 1 They grew the organism in a medium that had everything 2 complete medium the yeast grew In a different test tube they removed ornithine citrulline and arginine the yeast did not grow this was the negative control meaning that they were not looking for it to grow 3 Then they created 3 different mutant versions of the yeast 4 Mutant 1 removed Arg1 does not have the gene Arg1 this is the same as Enzyme 1 so ornithine could not be made 5 Mutant 2 removed Arg2 does not have gene Arg2 no Enzyme 2 so citrulline could not be made 6 Mutant 3 removed Arg3 does not have gene Arg3 no Enzyme 3 so arginine could not be made 7 Mutant 1 Arg1 without ornithine 8 Mutant 2 Arg2 without citrulline 9 Mutant 3 Arg3 without arginine 10 Medium ornithine no citrulline no arginine Arg1 the yeast grows Arg2 the yeast does not grow Arg3 the yeast does not grow 11 Medium citrulline no ornithine no arginine Arg1 the yeast grows as long as you have citrulline you can make arginine Arg2 the yeast grows Arg3 the yeast does not grow 1 12 Medium arginine no ornithine no citrulline Arg1 the yeast grows all you are trying to make is arginine so if you can given it then the yeast will grow it does not matter if you don t have the things that come before arginine because the goal of the previous components was to make arginine Arg2 the yeast grows Arg3 the yeast grows II Transcription involves converting one of the strands into RNA A Only 1 strand serves as the template the other strand does not have anything to do with making the RNA B The template is called the antisense strand the non template is called C The template strand is called the antisense strand because the mRNA the sense strand is complementary to it D The non template strand is called the sense strand because the mRNA is identical to it except U is used in mRNA while T is used in the DNA E The template and non template strands switch up from gene to gene there is not a set template and set non template strand for all genes III F You can make 2 messenger RNAs from a double stranded DNA Promoters and consensus sequences A The colored regions are regions in the DNA that do not code for anything but they allow transcription to happen B Promoter region upstream C 1 the first nucleotide where transcription is going to start D 2 promoter regions at 35 and 10 this is how many nucleotides the promoter regions are behind the start nucleotide E RNA polymerase is the enzyme that carries out transcription F RNA polymerase is going to be recruited to the promoter regions G In bacteria RNA polymerase can see the promoter regions on its own it does not need any addition enzyme to bring it to these regions H Pribnow box the 10 promoter region in bacteria E Coli RNA Polymerase A The sigma factor is very important it recognizes the promoter first the 10 and the 35 regions it seeks out to find the RNA polymerase it binds to the promoters first initiates transcription B Beta prime the subunit that actually bind to the DNA C Alpha takes over once the sigma leaves binds to promoters D Sigma the first subunit that binds to the promoters Initiation and elongation stages of transcription in prokaryotes A After the first 10 nucleotides have been added initiation stops and elongation starts B Memorize the structure of RNA polymerase in bacteria C Transcription occurs in the 5 3 direction Active genes are transcribed many times A Certain genes are transcribed over and over house keeping genes B These types of genes look like a brush so they are called Lampbrush Chromosomes IV V VI 2 C Lampbrush Chromosomes are just transcribed over and over again extensive transcription occurs with these genes VII Termination of transcription the role of rho factors A Once the replication fork hits the termination sequence the Rho factor breaks the bonds between RNA and DNA it releases the RNA from the DNA and RNA polymerase goes away 3
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