Biology DNA Question - Help!

Please can some help me on this question. I understand that it codes in sections of 3 (codons) but I don't understand the numbering system to get the amino acids from the DNA strand.

Figure 2 shows the sequence of DNA bases coding for seven amino acids in the enzyme
ribonuclease.

Figure 2:

G T T T A C T A C T C T T C T T C T T T A

(Table Attached, second screenshot)

Amino acid Number present

Arg 3
Met 2
Gln 1
Asn 1

The number of each type of amino acid coded for by this sequence of DNA bases is shown
in the table.

Use the table and Figure 2 to work out the sequence of amino acids in this part of the
enzyme. Write your answer in the boxes below. (lines represent boxes)

(Gin) ____ ____ _____ _____ _____ _____

(edited 4 years ago)

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Reply 1

username5064508

16

Split the sequence up into codons, and see which ones are repeated. GTT and TTA both appear once, and you are told that there is only one Asn and one Gln in the sequence. As you know that the first one, GTT, corresponds to Gln, this means that TTA must correspond to Asn. TTA is the last codon, so in the last space in the answer line write Asn. TAC appears twice, and there are said to be two Met in the sequence, so TAC must be Met. Similarly, there are 3 TCTs, and you are told Arg appears 3 times, so TCT is Arg.

Reply 2

izaakha

OP

11

Original post by HRobson_BMC

Split the sequence up into codons, and see which ones are repeated. GTT and TTA both appear once, and you are told that there is only one Asn and one Gln in the sequence. As you know that the first one, GTT, corresponds to Gln, this means that TTA must correspond to Asn. TTA is the last codon, so in the last space in the answer line write Asn. TAC appears twice, and there are said to be two Met in the sequence, so TAC must be Met. Similarly, there are 3 TCTs, and you are told Arg appears 3 times, so TCT is Arg.

Thank you! I worked it out just after I posted, it was the way it was worded that threw me off.

Biology DNA Question - Help!

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