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November Development and heredity,3.Translation.docx

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York University
Natural Science
NATS 1610

Living Body-Development and heredity, Translation -sharing a common genetic code • Transplanting DNA (one species can be programmed to produce proteins of other species) o Ex. Firefly gene artificially inserted into a tobacco plant • The genetic code: converts the linear sequences of bases in DNA to the sequence of amino acids in proteins -during translation ribosomes interpret a series of codons along a mRNA molecule • DNA: carries code for protein primary structure • mRNA: codons-nucleotide triplets (each specifies a specific amino acid, 64 different codons) o degenerate: more than one codon can specify the same amino acid • tRNA: anticodons-nucleotide triplet at one end (complementary to codons) o allows binding of tRNA to mRNA codon (specific for each amino acid) • Ribosomes: add each amino acid carried by tRNA added to the growing end of the polypeptide chain - gene tic code: • 3 stop codons(UAA,UGA,UAG) • 1 start codon (AUG) -Addition (insertion) of a U shifts the reading frame and changes the codons and amino acids specified -transfer (tRNA)delivers “right” amino acid to the correct location within the mRNA/ribosome complex • tRNA has a specific 3D structure ~80 nucleotides long • at one end of tRNA anticodon base pairs with a complimentary codon on mRNA • at other end of rRNA binding sites for amino acid -Ribosomes enable the addition of each amino acid carried by tRNA to the growing end of polypeptide chain • composed of large and small subunits • discrete sites for tRNA binding and polypeptides synthesis o p site: peptidyl site o A site: aminoacyl sire (acceptor) o E site: exit site for used tRNA -Translation requires 3 steps 1. Initiation a. Determines the starting point (start codon) from which all codons will be read during protein synthesis i. mRNA leaves the nucleus and enters cytoplasm ii. small ribosomal subunit moves along mRNA (from 5’ to 3’ end) until it reached first AUG codon iii. initiator tRNA with UAC anticodon and carrying MET (methionine) binds to AUG codon on mRNA (at P site) iv. large ribosomal subunit joins the small subunit to complete ribosome v. second binding sitre (A site) in ribosome (exposing second codon on mRNA) is ready for next tRNA with appropriate anticodon an amino acid 2. Elongation a. Addition of new amino acids and formation of peptide bonds b. As ribosome moves in 5’ to 3’ direction on coding sequences of mRNA 3. Termin ation a. E n
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