BRCA1 gene produces hereditary breast cancer if mutated. Suppose a mutation occu
ID: 215658 • Letter: B
Question
BRCA1 gene produces hereditary breast cancer if mutated. Suppose a mutation occurs within the BRCA1 gene at the position shown in red, and the pyrimidine (T) is substituted by a (C). The mutant DNA is shown below. What is the final effect of this base change on the resulting polypeptide? (Hint: UUG encodes Leucin).
Mutant DNA sequence 3'…A A C A C C C A G G A G C C… template strand
5'…T T G T G G G T C C T C G G… non-template strand
Protein sequence ......… - Leu
The mutant polypeptide has the same length with a totally different sequence of amino acids as of the normal one.
The mutant polypeptide has the same length as of the normal polypeptide but differs in just one amino acid.
This is a nonsense mutation, and the mutant polypeptide is shorter than the normal one.
This is a sense mutation, and the mutant polypeptide is longer than the normal one.
A.The mutant polypeptide has the same length with a totally different sequence of amino acids as of the normal one.
B.The mutant polypeptide has the same length as of the normal polypeptide but differs in just one amino acid.
C.This is a nonsense mutation, and the mutant polypeptide is shorter than the normal one.
D.This is a sense mutation, and the mutant polypeptide is longer than the normal one.
Explanation / Answer
This is a nonsense mutation and the mutant polypeptide is shorter than the normal one because when Leucine is formed with help of TTG, we have the frame which reads TGG. When this is converted into UGG, the sequence stops as it is a stop codon. This prevents further addition of the nucleotides and formation of the sequence completely stops after leucine
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