5. Nirenberg and Matthaej as well as Khorana were able to synthesize RNA molecul

Question

5. Nirenberg and Matthaej 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 UUwwuI... 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: GU 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? Name Recitation Section How could this experiment be used to support the hypothesis that the genetis code uses a triplet code?

Explanation / Answer

G... - 1 amino acid (Gly)

GU... - 2 amino acids (Val, Cys)

GUA... - 2 amino acids (Val, 1 stop codon, Ser)

GUAC... - 4 amino acids (Val, Tyr, Thr, Arg)

GUACC... - 5 amino acids (Val, Tyr, Thr, Pro, Arg)

GUACCG... - 6 amino acids (Val, Tyr, Thr, Pro, Arg, Gly)

GUACCGA... - 7 amino acids (Val, Tyr, Thr, Pro, Arg, Glu, Ser)

GUACCGAG... - 8 amino acids (Val, Tyr, Thr, Pro, Arg, Glu, Arg, Gly)

GUACCGAGU... - 9 amino acids (Val, Tyr, Thr, Pro, Arg, Glu, Ser, Val, Cys)

This experiment could be used to support the hypothesis that the genetic code uses a triplet code as three nitrogen bases constitute a codon which specifies the placement of one amino acid in a polypeptide.

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