Question

What peptide would you expect to result from a 21-nucleotide-long DNA sequence that contains only the base adenine?

Answer 1

a peptide composed of 7 phe
a peptide composed of 21 phe
a peptide composed of 7 lys
or a peptide composed of 21 lys?

Answer 2

To answer this question look up the genetic code - ie which codons represent which amnio acids. Then figure out how many amino acids there are per codon (a codon is three nucleotides of course). To help I've included a link to the correct chart:

http://en.wikipedia.org/wiki/Genetic_code

You should look where it says "RNA codon table"

Answer 3

Id appreciate it if you'd actually talk me through the answer than give me a link to wikipedia and tell me to look it up...

Answer 4

@ebaxter01

Answer 5

So, remember that A-T bonding occurs, thus when the DNA is transcribed to mRNA it will code to A-U thus you will have a 21-Uracil long dodecamer mRNA. If we look up with the codon UUU codes for, we will find it codes for Phenylalanine.

Since the amino acids code based off then mRNA codons: 21/3 = 7 so we will have:
A. a peptide composed of 7 phe

hope that helps.

Answer 6

Hi, sorry if you didn't get the hang of this question from my initial answer. agreene has brought up base pairing and indeed this is the case. However the DNA sequence on the coding strand looks like the mRNA sequence. This is getting to be a contentious problem, possibly because the initial question wasn't clear about whether the polydA strand was coding or not. If not then we have polyU transcribed and polyphenylalanine results. If the DNA was the other way round then 7 lysines would be translated.