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CHAPTER 14.docx

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Biology 1002B
Tom Haffie

141 THE CONNECTION BETWEEN DNA RNA AND PROTEINSBeadleTatum s experiment Lead to the one gene onepolypeptide hypothesisTheir subject was neutospora a type of bread mouldo Two variteswild type and mutant by exposing to xrayso Each group was grown in minimal growth mediummutant did not grow unless supplied with additional nutrients ex amino acidarginine Arg mutantsthey hypothesized had a deficiency in an ezyme needed for the synthesis of argenine Why is it a triplet codeScientists knew that there were 20 amino acids if 1 base pair coded for 1 aa4 aasIf 2 base pairs coded for one aa4216 amino acidsso smallest possible number is 3 4364 NirenbergLeder synthesising all possible codons and combining them in a mixture of tRNAs and Khorana synthesising long and repeatative mRNAs and mixing with ribosomes experiments helped plot the genetic codeSense codonsthey specify a certain amino acid 61 of 64 codons are sense o AUGcodes for methionine it is the start initiator codonNonsense termination codonshave no corresponding amino acido UAA UAG UGAGenetic code is degenerate more than one codon for more amino acidsIt is also commalessmust be read in the correct manner to make sense 142 TRANSCRIPTION DNADIRECTED RNA SYNTHESIS Transcription is not replication o mRNA is single strandedo RNA polymerase not DNA polymerase catalyses rxns RNA polymerase doesnt need a primer eithero Only the part coding for gene takes part in transcription not entire genome o At a given point in timeonly one DNA strand acts as template Protein coding and nonprotein tRNA mRNA snRNA rRNA regions exist Promoter Transcription unitthe part bw promoter and terminator that is transcribed as mRNA the new RNA molecule temporarily winds with the template strand of DNA into a hybrid RNADNA double helix template strand read 35o 5 end of RNA is made first IN EUKS o They have a TATA box sequence right before the promoter that forms complex with transcription factorstogether they attract the RNA polymerase II and DNA begins to unwind
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