Question

How does Aspartic acid mutated to glycine?

What are the effects of the mutation to a protein? What would is change

Answer 1

Mutation is sudden, inheritable, discontinuous variation due to change in chromosomes and genes. A mutation in DNA alters the mRNA, which in turn can alter the amino acid chain. If gene mutation arise due to change in single base pair of DNA, it is called point mutation and may take place by deletion, insertion and subsitution of one or more bases in a nucleotide chain. Base substitution have three diffrerent effects in a protein. It can cause mis-sense mutation, non-sense mutation and silent mutation. Change in base in a codon, producing a different amino acid at the specific site in a polypeptide is called mis-sense mutation. Non-sense mutation arise when a normal codon, coding for an amino acid is changed into a chain terminating codon (UAG, UAA, UGA), resulting in the production of an incomplete polypeptide. Silent mutation are mutations in DNA within a protein coding portion of a gene that does not affect the sequence of amino acids that built the gene's protein.

The codon in the mRNA that codes for Aspartic acid (Asp) is GAU and GAC. The middle base of a DNA triplet coding for the amino acid aspartic acid is mutated so that the triplet now codes for glycine (Gly) instead. The DNA template strand having the triplet sequence CTA and CTG via transcription codes for aspartic acid in the triplet codon, GAU and GAC in mRNA. But when the middle base, T of the DNA triplet coding for aspartic acid is mutated with the substitution of T by C, it produces triplet codon GGU and GGC in the mRNA that now codes for amino acid Glycine. This is how aspartic acid is mutated to glycine via substitution (transition) of the gene coding for aspartic acid.

This will simply results the expression of glycine amino acids in place of aspartic acid in the protein molecule, as a result of mis-sense mutation.

Another similar example of mis-sense muation is found in case of sickle cell anaemia which is caused by mutation (transversion) of the gene controlling beta-chain of haemoglobin. It replaces glutamic acid (Glu) present at 6th position of the beta-chain by amino acid valine (Val). Here also the middle base of a DNA triplet coding for the amino acid glutamic acid is mutated so that the triplet now codes for valine instead.