The base sequence of a section of DNA is shown below.
C A T G C A C A T C G T G C C C A A
The maximum number of different amino acids this section codes for is:
A. 4
B. 5
C. 6
D. 9
E. 18
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The answer is B, there are 5 different amino acids that the given sequence codes for.
We know that in the process of transcription-translation-replication that are involved with amino acids and proteins, that codons are made up of 3 nucleotides.
The question is asking for the maximum number of different amino acids:
- Count the number of nucleotides, and divide that by 3, since that is the minimum number of nucleotides that make up a codon. In this case, there are 18 total nucleotides, giving a total of 6 codons.
- However, what’s being asked are the maximum number of different amino acids, which means that you should not consider any repeating codons when you count.
- If you notice, the sequence C A T happens twice. We know that the genetic code is unambiguous, which means that each codon specifies one amino acid only. Thus, it is not possible that the sequence C A T specifies more than 1 amino acid.
Therefore, there is a maximum of 5 different amino acids that the given sequence codes for given that there are only 5 unique codons (CAT, GCA, CGT, GCC, CAA)
Reminders:
- Remember to always read the sequence given! Do not just count! and read the question very carefully to discern what it’s asking for.
2 Likes
But GCA and GCC also coding for the same amino acid which names Arg, so I may think the answer is A, but if you’ll start coding from the second nucleotide you’ll get five different amino acid and this is the reason why B is the answer.
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also I doubt the IMAT will expect us to know ALL the codons correlating with AA. I hope this is the case lol if not well thats pretty brutal