lec 3 notes.docx

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Stavroula Andreopoulos

TRANSLATIONlec3Interactions between tRNAs adaptors that bring aas when they read mRNA codons allows for translation of genomic sequences into proteinsEg Prokaryotic 70S ribosome 50S30S is composed of rRNAproteins50S is the large catalytic subunit with EPA sites tRNA enters the Asite to allow translation to go from 53 on mRNA and peptide CONH formation NTDCTDEach EPA site has a different tRNA so tRNAs are structurally similar yet unique to recognise and attack specific codons30S is small noncatalytic subunit where mRNA enters the ribosome3 Elucidation of the genetic code was done by George Gamour where 1 word1 codon ie 4for 3letter codon64 codons some replicatedExperiment Synthetic multiple repeats of UUUnPhe residues stst 1 codon identified1 aaUUU UUCie trinucleotide repeats denote polypeptide productsKey features of the genetic code1All living organisms use the genetic code prokseuks via an unambiguous codon triplet of nts in the mRNA in the correct reading frame2Codons are translated 53 so nts are written accordingly Genetic code is degenerate so multiple codons code for same aa Anticodons are read 53 as well but they are arranged 35 to the mRNArd 3Synonyms are codons that specify the same aa but have different nt in the 3position eg PheUUU UUC4Genetic code is nonoverlapping so every triplet denotes a specific codon that has no punctuation ie abcdefwhere bpart of codon 25First 2 positions of a codon tells whether the aa is hydrophilic or hydrophobic ndie at 2 position purinepolarpyrimidinehydrophobic6Only 6164 codons specify aas the other 3 codons are stop codonsUAA UAG UGA which are not read by tRNA7Codons for only 1 aa AUGMetUGGTrp
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