Genetics: Consider the experiment by Nirenburg and colleagues. In a series of ex

Question

Genetics: Consider the experiment by Nirenburg and colleagues. In a series of experiments, the scientists produced polypeptides using an in vitro (cell-free) translation system and random RNA templates made from mixtures of nucleotides. They then analyzed the amino acid content of the polypeptides that were translated from these RNA templates. In the textbook example, from random RNA templates made of 70% Guanine and 30% Uracil, the polypeptides contained 6% Cysteine, 49% Glycine, 6% Leucine, 3% Phenylalanine, 15% Tryptophan, and 21% Valine.

In one follow-up experiment, the scientists used an RNA template made from 80% Adenine and 20% Cytosine Nucleotides as a template for in vitro translation. Given this, answer the two questions:

1.) Given what we know now, what would be the expected percentage of each amino acids produced (you can simply say "the rest are not produced" for those at zero % ).

2.) Given only the expected results from this experiment, that you present above, can you identify which amino acid is produced from any given codon? If so, which codon or codons produce which amino acid?

Explanation / Answer

1. The expected codons are AAA = Lysine; AAC = Aspergine; ACA = Threonone, CAA = Glutamine; ACC = Threonine; CCA = Proline; CAC = Histidine, CCC = Proline. Afetr translation, the expected percentage of Amino acids in the peptide: Lysine = 24% (8+8+8); Aspergine = 18% (8+8+2); Threonine = 18+12 = 30%; Glutamine = 18%; Proline = 12+6 = 18%; Histidine = 6%. It is calculated by scoring as follows: 'A' score = 8 & 'C' score = 2

2. By polymerizing Adenine nucleotides, we can get poly A mRNA, which upon translation gives Poly Lysine peptide. Similarly by polymerizing Guanine, Cytosine, and Uracil nucleotides we can get the respected amino acids homopoly peptides. Then by mixing 2 different nucleotides in different ratios like 9:1 or 8:2 or 7:3 etc, we can deduce all the codons and their coding amino acids.

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