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Lecture 12

BIO206 Lecture 12 Chapter 7.pdf

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Department
Biology
Course
BIO206H5
Professor
George S Espie
Semester
Fall

Description
Lecture 12 Chapter 7October1613512 PMDeciphering The Genetic Codediagram shows explanations of each of the characteristics of the code tripletis 3 bases per amino acid commafreemeans that the codons follow right after another at bottom can see could use one base like A or every 4th base as a spacer there wasnt any spacing in between codonsnonoverlappingone codon finishes before the next one starts all of these sequences are nonoverlappingdegenerateagain means more than one codon for at least some amino acidsNirenberg Matthaei and Khorhana 1960sCellfree protein synthesizing systempolyU UUUUUUU ONLY polyPhe PhePhePhepolyA AAAAAAA ONLY polyLys LysLysLyspolyC CCCCCCCC ONLY polyPro ProProPro Then used copolymers 1 nucleotide containing 234 codonsto infer other codes for amino acidstechnology to sequence RNA and proteins had not been developed so they couldnt just compare sequences of the twotheir system gently lysed bacterial cells centrifuged to remove cell membranes etc left with all the things needed to make protein CELL FREE SYNTHESIZING SYSTEMproved by adding ATP GTP and amino acids and carbon14 that protein synthesis occurred you could tell by incorporation of carbon14 into the proteins produced by the system there wasnt any in the proteins before now there wastreated with DNAse to remove endogenous DNA system is readyadded synthetic DNA polymers and analysed composition of the polypeptides they got poly U etcCANT DO GGGGG it assembles into a mess then used more complicated synthetic DNA to work out the rest of the codeCODONGroup of bases that specifies a single amino acid The code is read in units of 3 nucleotides3 bases per codon triplet64 combinations Synonyms codons that specify the same amino acid44 combinations unused OR code is degenerateDegenerate Amino acids specified by more than one codoneg Cysteine has two codons UGCUGUthe code has extra spaces available cells actually make use of all of the codons however so that means that the code must have more than one amino acid specified by each codonThis is what it means when the code is referred to as degenerateThe Standard Genetic Code61 of 64 codons encode amino acidsFrom 26 synonyms per amino acidSynonyms usually 3rd position wobble2nd position if more than 4 synonyms eg LeuAUG metis also start codon Book Notes Page 1
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