Translation Imagine that scientists have discovered extrater

Translation

Imagine that scientists have discovered extraterrestrial bacteria, which arrived on earth via a meteorite. Nucleic acids and proteins were found as components of this organism, but the nitrogenous base composition of the nucleic acids different than that earth-based forms. Specifically, RNA the bacteria consisted of four different bases called W, X, Y and Z. You are assigned to decipher the genetic code of this creature and decide to emulate the Nobel Prize-winning approach of Khorana, Nirenberg and Ochoa by synthesizing polynucleotides, which are translated in all possible reading frames, and using this information to determine the amino acid sequences made from these polynucleotide sequences. You obtain the following data: Synthetic nucleotide Peptide sequence obtained A. 5\' XYXYXYXYXYXY....3\' Pro-Leu-Pro-Leu-Pro-Leu B. 5\' ...XXYXXYXXYXXY....3\' Pro-Pro-Pro... OR Ala-Ala-Ala... OR Thr-Thr-Thr C. 5\' XXXYXXXYXXXY.....3\' (Trp-Thr-Pro-Ala peats 1. Consider each of the three possible reading frames for sequence A (in other words, start with the first letter of the sequence, then the second, then the third). What are the possible codon sequences for each frame? 2. Based on your findings in 1), what are the possible codons for Pro? 3. Using the same approach as you just took for sequence A, write out the three possible reading frames for sequence B. Based on sequences A and B, what is the codon for Pro? What about Leu?

Solution

1. Considering all the possible reading frames for sequence A:

Frame 1 has following codons: XYX-YXY-XYX-YXY
Frame 2 has following codons: YXY-XYX-YXY-XY
Frame 3 has following codons: XYX-YXY-XYX-Y

2. Since proline and leucine are alternating, proline has either XYX or YXY as its codon, because only the frames 1 and 2 give an alternating pattern of codons.

3. Considering all the possible reading frames for sequence B:

Frame 1 has following codons: XXY-XXY-XXY-XXY
Frame 2 has following codons: XYX-XYX-XYX-XY
Frame 3 has following codons: YXX-YXX-YXX-Y

We can see that XYX is common in both sequences A and B. And both contain proline. So the codon for proline is XYX. As far as leucine is considered, it will occupy the remaining alternating codon i.e. YXY.

4. Considering all the possible reading frames for sequence C:

Frame 1 has following codons: XXX-YXX-XYX-XXY
Frame 2 has following codons: XXY-XXX-YXX-XY
Frame 3 has following codons: XYX-XXY-XXX-Y