Question

Determine the amino acid chain coded for by the following sequence. Suppose a mutation occurs where another A is added after the first codon. What would the new sequence of amino acids be? Normal DNA: T G G A G T C G A G G T Normal RNA: Amino Acids: Mutant DNA: T G G A A G T C G A G G T Mutant RNA: Amino Acids: Why are frameshift mutations likely to cause more problems than a point mutation?

Answer 1

Answer:

Normal DNA: T G G A G T C G A G G T

Normal RNA: A C C U C A G C U C C A

Normal amino acids: Theronine - Serine - Alanine - Proline

Mutant DNA: T G G A A G T C G A G G T

Mutant RNA: A C C U U C A G C U C C A

Mutant amino acids: Theronine - Phenylalanine - Serine - Serine

Explanation:

Frameshift mutations cause more serious problems as compared to point mutations because in frameshift mutations the entire reading frame changes after the insertion or deletion of a nucleotide. Change in the reading frame further leads to the incorporation of all wrong amino acids after the insertion/deletion.

For example in the given question, in normal DNA which is T G G A G T C G A G G T after TGG the next codon is A G T but in mutant DNA after TGG a wrong nucleotide which is A has been inserted which is causing the rest of the triplet codons to change. As a result of this insertion, the entire amino acids which are being added subsequently are different than the original peptide chain. In the given question, Theronine - Serine - Alanine - Proline is the original peptide chain but because of frame shift mutation the entire peptide chain has changed after threonine with the amino acids Theronine - Phenylalanine - Serine - Serine in the mutant chain.

In contrast to this, a point mutation causes the insertion of a wrong nucleotide by replacement of the original nucleotide and does not cause insertion or deletion of any nucleotide. As a result of this replacement only one amino acid in the chain differs and rest of the amino acids remain the same as of the original peptide. So, the severity of disease is comparatively less.

For example: In the given question if 4th nucleotide which is 'A' is replaced by G then DNA will be  T G G G G T C G A G G T and RNA will be A C C C C A G C U C C A. The peptide chain synthesized from this RNA will be Theronine - Proline - Alanine - Proline. Only one amino acid which proline is different than the original peptide chain so the severity of disease is less because a protein with just one or two different amino acids in the peptide chain can still work but if there will be more amino acids which are different from the original protein then protein may become non-functional.