Question

Suppose, you synthesized RNA in vitro using polynucleotide phosphorylase, 3 parts ADP and one part GDP After the reaction, you isolated all RNA molecules and translated them in a cell-free translation system. Now, answer the following questions. (A) How many different amino acids do you expect in the polypeptides synthesized in the cell-free system? Name these amino acids. Use the codon dictionary available in the textbook. (B) Which amino acid would show highest frequency of incorporation in the polypeptides synthesized in the cell-free system? Show your calculations for full credit. 5 pts

Answer 1

Since the RNA contains only two nucleotides, A and G, the possible codons would be

AAA, AAG, AGA, GAA, AGG, GGA, GAG, and GGG.

AAA- Lys

AAG- Lys

AGA- Arg

GAA- Glu

AGG- Arg

GGA- Gly

GAG- Glu

GGG- Gly

Four different amino acids (Lys, Arg, Glu and Gly) would be present in the polypeptides.

Amino acid with highest frequency

Codon has three nucleotides.

The probability that ‘A’ occupies the a position in the codon= ¾

The probability that ‘G’ occupies the a position in the codon= ¼

Therefore, the probability for AAA codon to occur has higher probability (3/4 x ¾ x ¾ )

Therefore, Lysine would be the most frequent amino acid.

The probability for GGG codon would be least (1/4 x ¼ x ¼)