You are studying a new species of microorganism that was discovered at the botto

Question

You are studying a new species of microorganism that was discovered at the bottom of the ocean and appears to have been isolated from other species for millions of years. You begin analyzing the species and you realize that it does still use the same four bases of DNA and RNA that are found in the rest of living organisms - you know this because you sequenced the DNA that encodes several proteins. However, when you begin to analyze its proteins, you realize that none of the proteins contain the amino acid Alanine, only the 19 other common amino acids. Assume that the organism uses the standard triplet code in explaining your answers.

A. What are two possible explanations for why none of the proteins have the amino acid Alanine present?

B. How would you determine whether either of these two possibilities are likely to be correct? If possible, please describe the experiment and include the experimental set-up used by Nirenberg and Leder if possible to test one of your hypotheses. Assume you can isolate the ribosomes and charged tRNAs from this species and specifically radiolabel each amino acid.

Explanation / Answer

According to standard genetic code, Ala is encoded by the following four triplet codons.

i. GCA

ii. GCU

iii. GCG

iv. GCC

Hypothesis I: The given organism does not contain alanine biosynthesis pathway. Ala codon could be used as stop codons.

Hypothesis II: The organism contains Ala biosynthetic pathway. But, Ala is not incorporated into proteins as it does not Ala-tRNA. The Ala codons could be used to encode some other amino acid.

To test these possibilities, we can artificially synthesize, Poly-GCN trinucleotide repeat sequence and use it for invitro translation using bacterial translation machinery and the translation machinery isolated from the organism. Sequencing of the resulting peptide will tell what is the actual scenario.

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