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

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

4 Likes

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.

2 Likes

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