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

Question

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 UUUUU... 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: G… GUA... GUAC... GUACC... GUACCG... GUACCGA GUACCGAG How many amino acids do you expect to make up a repeating unit in the polypeptides produced from these RNAs? GUACCGAGU Name Recitation Section How could this experiment be used to support the hypothesis that the genetic code uses a triplet code?

Explanation / Answer

For mRNA we get a repeating nucleotide structure for which we get a certain repeating set of amino acids (single-letter format)
G... = GGG... = 1 Amino acid of G
GU... = GUGUGU = 2 Amino acid of VC
GUA... = GUA = 1 Amino acid of V
GUAC... = GUACGUACGUAC = 4 Amino acid of VRTY
GUACC... = GUACCGUACCGUACC = 5 Amino acid of VPYRT
GUACCG... = GUACCG = 2 Amino acid of VP
GUACCGA... = GUACCGAGUACCGAGUACCGA = 7 Amino acid of VPSTEYR
GUACCGAG... = GUACCGAGGUACCGAGGUACCGAG = 8 Amino acid of VPRYRGTE
GUACCGAGU... = GUACCGAGU = 3 Amino acid of VPS

This experiment can be used to support the hypothesis that the genetic code uses a triple code, because whatever the length of the repeating nucleotide might be, once it starts repeats itself enough times to yield a number divisible by 3, we see that even the polypetide produced starts repeating itself in tandem. ANSWER

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