Elucidating Codons with Random Copolymers

Before we got a codon table as we know it today, scientists had to figure out what the letters were in each of the 64 combinations of triplets of nucleotides.  It is child's play to get all the possible codons, but what they mean is another story!

The level of technology at the time was that random polymerization in vitro (that is, in a testtube with enzymes, buffers, and whatever nucleotides the scientist put into the tube) was possible, but precise construction of synthetic mRNAs wasn't an option.

So, scientists created synthetic mRNAs that contained only, say, uracil and cytosine.  To distinguish between U and C content of each codon, they ensured that the proportion of U would not equal C.  Thus, they knew if 80% C and 20% U were used, the most common codon would be CCC and the least common would be UUU.  The number of CCC would be 0.8³ and UUU would be 0.2³.

Using this logic, answer the following question:

• A scientist creates a random copolymer from a solution containing all 20 amino acids, 40% guanine, 60% cytosine, and appropriate enzymes.

• She then does in vitro translation and isolates only the oligopeptides that were formed.

• Your job is to calculate which amino acids were in the polypeptides formed and the proportion of each represented.

Try this for yourself before accessing the answer below ...

NEW! Interactive Exercise (click here)