Question

DNA strand: TTTTCGCGATATGCTGGT The following set of protein chains (amino acids) were created by mutating one nucleotide in the DNA strand above. For each of the protein chains, identify the mutation to the DNA strand as a codon deletion, addition, or substitution. Describe how you identified the mutation. Protein Chain 1: PHE-SER-ARG-ASP-ALA-GLY Protein Chain 2: PHE-SER-ARG-MET-LEU Protein Chain 3: PHE-SER-ARG-LEU-CYS-TRP

Answer 1

The DNA sequence TTT TCG CGA TAT GCT GGT codes for the following amino acids: PHE-SER-ARG-TYR-ALA-GLY.

Protein Chain 1 is a substitution. The nucleotide at position 10 (T) is changed into a G resulting in the following DNA sequence: TTT TCG CGA GAT GCT GGT. The amino acid TYR is then changed into an ASP.

Protein Chain 2 is a deletion. The nucleotide at position 10 (T) is deleted and the resulting DNA sequence is TTT TCG CGA ATG CTG GT. There is then a different reading frame after nucleotide 9, which causes the amino acid sequence to change after the ARG.

Protein Chain 3 is an insertion (addition). After nucleotide at position 9, a C is added resulting in the following DNA sequence TTT TCG CGA CTA TGC TGG T. There is, as for protein chain 2, a different reading frame after nucleotide 9, which causes the amino acid sequence to change after the ARG.