NASA has identified a new microbe present on Mars and requests that you determin
ID: 51997 • Letter: N
Question
NASA has identified a new microbe present on Mars and requests that you determine the genetic code of this organism. To accomplish this goal, you isolate an extract from this microbe that contains all the components necessary for protein synthesis except mRNA. Synthetic mRNAs are added to this extract and the resulting polypeptides are analyzed:
Synthetic mRNA
Resulting Polypeptides
AAAAAAAAAAAAAAAA
Lysine-Lysine-Lysine etc.
CACACACACACACACA
Threonine-Histidine-Threonine-Histidine etc.
AACAACAACAACAACA
Threonine-Threonine-Threonine etc.
Glutamine-Glutamine-Glutamine etc.
Asparagine-Asparagine-Asparagine etc.
1) From these data, what specifics can you conclude about the microbe's genetic code?
2) What is the sequence of the anticodon loop of a tRNA carrying a threonine?
3) If you found that this microbe contained 61 different tRNAs, what could you speculate about the fidelity of translation in this organism?
Synthetic mRNA
Resulting Polypeptides
AAAAAAAAAAAAAAAA
Lysine-Lysine-Lysine etc.
CACACACACACACACA
Threonine-Histidine-Threonine-Histidine etc.
AACAACAACAACAACA
Threonine-Threonine-Threonine etc.
Glutamine-Glutamine-Glutamine etc.
Asparagine-Asparagine-Asparagine etc.
Explanation / Answer
1) The specifics we can conclude about the genetic code are the codes that are specific for various proteins. These codes are:
AAA- lysine
ACA- Threonine
CAC- Histidine
GAA/GAG- Glutamine
AAU/AAC- Asparagine
2) The anticodon loop carrying threonine will be 3' UGU 5' trna.
3) 61 different tRNAs implies that twenty amino acids will have 61 anticodons. This means that A,T,G,C bases will have three letter codons complimentary to anti codons in 5' to 3' direction. This means that the 3 base codons can be made resulting into 4X4X4 = 64 possible codons for 20 amino acids. We can speculate that there will be tRNA 61 anti codons on trnas and 3 codons can be there as stop codons for translation. Thus, we can infer that microbes on Mars are translating proteins same way as microbes on earth do.
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