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The following base sequence is given for the DNA coding strand: 5' ACTGTTACATTG 3'. Insertion of the base thymine (T) between the 8th and 9th base may affect how many amino acids?
A. 0
B. 1
C. 2 correct answer
D. 3
I chose C but it seems like it was for the wrong reason. Their explanation is "Without the insertion of the extra base, the sequence generates four amino acids from four tRNA anti-codons – UGA, CAA, UGU, AAC.
With the extra base inserted, the third tRNA anti-codon changes from UGU (cys) → UGA (stop), and the fourth tRNA anti-codon changes from AAC (asn) → UAA (stop). The first two amino acids are unaffected, but the third and fourth amino acids are affected. This is a particularly important insertion since the third codon is a stop codon that will terminate the protein."
The way I approached it was realizing that the mRNA would be 5' ACU-GUU-ACA-UUG 3'. Then inserting T into the DNA would mean the RNA becomes 5' ACU-GUU-ACU-AUU-G 3'. However, I don't understand why the answer explanation takes into account the anti-codons UGA and UAA as signifying the stop signal. Aren't UGA and UAA considered stop codons when they are part of the mRNA, not the anti-codon?
A. 0
B. 1
C. 2 correct answer
D. 3
I chose C but it seems like it was for the wrong reason. Their explanation is "Without the insertion of the extra base, the sequence generates four amino acids from four tRNA anti-codons – UGA, CAA, UGU, AAC.
With the extra base inserted, the third tRNA anti-codon changes from UGU (cys) → UGA (stop), and the fourth tRNA anti-codon changes from AAC (asn) → UAA (stop). The first two amino acids are unaffected, but the third and fourth amino acids are affected. This is a particularly important insertion since the third codon is a stop codon that will terminate the protein."
The way I approached it was realizing that the mRNA would be 5' ACU-GUU-ACA-UUG 3'. Then inserting T into the DNA would mean the RNA becomes 5' ACU-GUU-ACU-AUU-G 3'. However, I don't understand why the answer explanation takes into account the anti-codons UGA and UAA as signifying the stop signal. Aren't UGA and UAA considered stop codons when they are part of the mRNA, not the anti-codon?
