Describe point mutations, nonsense mutations, and frameshift mutations. Discuss the likely effect of each type of mutation on a protein being built

Question

What will be an ideal response?

Answer 1

A point mutation occurs when one nucleotide is substituted for another. Point mutations sometimes change the sequence of amino acids in a protein. For example, a mutation from AAC to AAG would replace asparagine with lysine. Not all point mutations affect amino acids, however: A mutation from GCA to GCC would have no effect because both codons code for alanine. Does a change in a single amino acid really matter? Sometimes it does and sometimes it doesn't. The sickle cell hemoglobin allele differs from normal hemoglobin by only one amino acid. In addition, for proteins that function as enzymes, the lock-and-key fit of enzyme to substrate can be disrupted by a single amino acid change. A nonsense mutation creates a stop codon in the middle of a protein-coding sequence. Nonsense mutations result in the production of shorter, often nonfunctional proteins. The insertion and deletion of nucleotides can result in a frameshift mutation. In a frameshift mutation, the triplet codons that are "read" and translated are shifted, completely altering the amino acid sequence in the protein being assembled. Frameshift mutations usually have significant disruptive effects on proteins.