Question

The Genetic Code was cracked by several different types of experiments. Some involved the synthesis of an RNA strand (that acted like a mRNA) that was used in cell-free extracts that could carry out protein synthesis. The ribosomes in the extracts could translate a polypeptide from the synthetic RNA without the normal requirements for translation (such as initiation factors, rbs, initiator tRNA, etc). Also, the ribosome could start translation at random locations along the RNA. What would the synthesized polypeptides look like using each of the following synthetic RNAs?
A. An RNA consisting of repeating sequences of GC.
B. An RNA consisting of repeating sequences of UA.
C. An RNA consisting of repeating sequences of GAC.

Answer 1

Answer:

A. Repeats of "Alanine-Arginine"

B. Repeats of "Tyrosine-Isoleucine"

C. Repeats of Aspartic acid

Explanation:

A. The synthetic RNA with GC repeats would have repeats to two codons: GCG and CGC which in turn code for alanine and arginine amino acids respectively.  Hence, its polypeptide would have repeats of "Alanine-Arginine"

RNA: GCG CGC GCG CGC GCG CGC  

Alanine-Arginine-Alanine-Arginine-Alanine-Arginine-Alanine-Arginine ...

B. The synthetic RNA with UA repeats would have repeats to two codons: UAU and AUA which in turn code for tyrosine and Isoleucine amino acids respectively.  Hence, its polypeptide would have repeats of "Tyrosine-Isoleucine"

RNA: UAU AUA UAU AUA UAU AUA

Tyrosine-Isoleucine-Tyrosine-Isoleucine-Tyrosine-Isoleucine-Tyrosine-Isoleucine

C. The synthetic RNA with GAC repeats would code for polypeptide of aspartic acid only as GAC codes for aspartic acid.

RNA: GAC GAC GAC GAC GAC GAC

Aspartic acid-Aspartic acid-Aspartic acid-Aspartic acid-Aspartic acid-Aspartic acid