Question

You are studying the protein MXP

in mice. There are several known MXP mutations. For each mutation you have extracted MXP DNA, mRNA and protein. The table below gives you information on each mutation relative to wildtype. Use the information given to determine what type of mutation has likely occurred in each mutant.

	Length of MXP DNA/gene	Length of MXP mRNA	Size of MXP protein	MXP mutant function	Type of mutation
Mutation 1	Same as wildtype	Longer than wildtype	Smaller than wildtype	Loss-of-function	choose ? "base pair subsitution (or) base pair insertion (or) base pair deletion" choose? "synonymous(silent) (or) nonsense (or) missens"
Mutation 2	Longer than wildtype	Same as wildtype	Same as wildtype	Same as wildtype	choose? "base pair subsitution (or) base pair insertion (or) base pair deletion" choose? "synonymous(silent) (or) nonsense (or) missens"

Mutation 3

Same as wildtype

Same as wildtype

Same as wildtype

Loss-of-function

choose? "base pair subsitution (or) base pair insertion (or) base pair deletion" choose? "synonymous(silent) (or) nonsense (or) missens"

Answer 1

1.- The protein produced is shorter but the nucleotide chains are not shorter, and the protein has lost its function. This is a base pair substitution that lead to a nonsense mutation. Thenucleotide substitution ended up producing an stop codon, this stop codon truncated translation and the final peptide is now shorter and nonfunctional

2.- Both nucleotides and protein maintain their native size and the protein is functional. This is a base pair substitution that lead to a silent mutation. The nucleotides susbtitution ended up coding for the same amino acid, so the final protein is just as functiona.

3.- All the molecule lenghts are just as the wildtype, but the protein lost the function. This is a base pair substitution that lead to a missense mutation. A nucletide was susbtituted and this caused the change in amino acid residues, this change enabled the protein to correctly arrange tridimentionally, thus the peptide is nonfunctional