C) Most of the mutations that Yanofsky recovered were missense mutations However

Question

C) Most of the mutations that Yanofsky recovered were missense mutations However, Yanofsky also recovered a nonsense mutation that changed amino acid number 15 into a stop codon. This codon normally encodes Lysine. Does the recovery of this mutation support the hypothesis that this Lysine residue is critical in the function of the tryptophan synthetase protein? Why or why not? 3. What does it mean that the genetic code is degenerate? 4.In eukaryotes and prokaryotes, what is the sequence of the initiator codon? 5. Nirenberg and Matthaei as well as Khorana were able to synthesize RNA molecules with repeating sets of nucleotides of various lengths and then analyze the amino acid sequence of the proteins that were encoded by these molecules. So for instance, RNA molecules of repeating single nucleotides such as U to give UUUU... or A to give AAAAA.... These give rise to single repeating amino acids. Repeating dinucleotides such as UC to give UCUcUcUC... These give rise to repeating units of 2 amino acids (Ser, Leu). Imagine that you carried out this experiment and made 9 RNA types composed of the following repeated sequences: GUA... GUAC … GUACC GUACCG... GUACCGA GUACCGAG GUACCGAGU How many amino acids do you expect to make up a repeating unit in the polypeptides produced from these RNAs?

Explanation / Answer

Q3) The genetic code is degenerate, i.e, it lacks specificity and one amino acids often has more than one code triplet. Only methionine and tryptophan have single triplet codons. All other amino acids are specified by 2 to 6 base triplets. Phenylalanine has two codons namely UUU and UUC. Arginine has six codons, viz, CGU, CGC, CGA, CGG, AGA and AGG.

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