Question

Explain how can changing one base in a segment of DNA can make a protein incapable of carrying out its biological role.

Answer 1

Ans) Some point mutations, insertion and deletions (indel mutations) can result in the alteration of the bases in the segment of a DNA. For example, in the DNA sequence TACTCCAGTTTC, When this will be transcribed we will have AUGAGGUCAAAG. But, if the DNA sequence i.e TACTCCAGTTTC has an alteration of a single base suppose by point mutation at the base number 8 (represented by bold letter) TACTCCACTTTC (i.e G is replaced by C). After this mutated DNA sequence is transcribed we get, AUGAGGUGAAAG. But, UGA is the stop codon and due this premature stop codon formation, AAG will not translate any protein.So, the translation can also get terminated prematurely when there is alteration in a single base of a DNA sequence. This was just one example.

Due to insertion and deletion mutations, the open reading frame (ORF) may get altered thereby coding for the different protein and this can result in the disruption of the protein function. For example, if valine is incorporated instead of glutamic acid at 6th position in the hemoglobin protein, this can result in sickle cell anemia because valine is hydrophobic amino acid and due to this, the abnormal assembly of subunits will occur in the quaternary structure of the hemoglobin protein and this results in sickle cell anemia.