Amino Acids, Proteins and Codons - Kaplan Question

[tshank]

This is Kaplan Test 3, Bio Question #17
Researchers isolated a polypeptide from the brains of goldfish trained to avoid darkness. This goldfish scotophobin was 15 amino acids long and differed from rat scotophobin by one amino acid. The gene for goldfish scotophobin must differ from that of rat scotophobin by:
Other passage info: The rat with scotophobin was also trained to avoid darkness.




A - one amino acid.




B - three codons.




C - at least one nucleotide.




D - at least three nucleotides.


The answers is C. But I don't understand. I though one nucleotide could be different and the protein could still come out the same? Or is the rule, one amino acid can change but the function of the protein - therefore avoiding darkness could be the same in both.
I thought one nucleotide could change but the same amino acid can be produced? Can someone help me out with transcription and relation to protein function? I know its a big topic. Thanks ya'll.

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[luxitas11]

The question is saying that one amino acid is different between the two proteins (i.e. they are both 15 a.a. long and one of those a.a. has a different identity in the two proteins). In order for two codons to produce different amino acids, they must differ by at least one base. If one base is different, you can possibly get two different amino acids. You might still get the same one, but in order to get a different one, at least one base must be different in the codons. You don't necessarily have to have all three bases different, so D would be wrong. You do necessarily have to have at least one base different, so C is the best answer.

 

[tshank]

Gotchya, that makes sense. I just need to think less "imaginatively." Thanks for the response!

 

[SN2ed]

Thread closed. These types of questions belong in the MCAT Study Q&A forum.