Question

10. Examine more closely how DNA changes in a co questions. Write the codon for the DNA sequence ATA then change only one nucleotide so that it codes for an RNA codon that is a STOP codon. If a codon changes to cause an mRNA to have a STOP codon instead of a codon for an amino acid, what type of protein mutation is this? Write the RNA codon(s) for histidine then change the last letter to a "G." What changes, if anything, in the protein that is produced? If a codon changes and it causes the amino acid sequence of the protein to change, what type of protein mutation is this?

Answer 1

1.If the DNA sequence is ATA the codon is complementary to it and in RNA thymmine is replaced by uracil so the codon will be UAU (which codes for tyrosine). If the final U is changed to A then the codon becomes UAA which is a stop codon.

2. The mutation that causes the change of an aminoacid coding codon to a stop codon is called a nonsense mutation and it generally leads to a shortened protein / peptide.

3. The codons for Histidine are CAU and CAC. If the last letter is changed to G , then the codon becomes CAG which codes for Glutamine. So glutamine will be present in the primary structure of the protein instead of histidine, which might lead to further structural and functional changes in the final protein.

4. The point mutation in the codon that leads to a change of amino acid sequence is known as missense mutation. Insertion, deletion or substitution of 1 or 2 bases may also result in change in aminoacid sequence due to frame shift mutation.