Point mutation question

Question

How can a point mutation result in a bad protein consisting of amino acid sequence different from the wild type protein? Thanks!

Answer 1

The change of one nucleotide can drastically change the sequence of amino acids in a protein.

For example, the code is groups of three letters so we'll create a genetic code such as "The dog saw the cat!"  Now change the sentence to "The dog saw the rat!"  It still makes sense but not the same as the first.  So this could generate a functional protein.  Now drop a letter from one of the codons such as, "The ogs awt hec at!"  Now the sentence is nonsense and any protein made from this sentence would be non-functional.  If the sentence has an extra letter inserted, then it could read, "The dog ssa wth eca t!"  Again the sentence is scrambled and non-functional.  In some cases in which there are more than one codon for an amino acid, the sentence could still mean the same thing but be different.  "The Dog saw the cat!" could produce the proper protein.  Here is a link for the table of amino acids and genetic codes:  http://users.rcn.com/jkimball.ma.ultrane...

Ultimately, the insertion of a different amino acid in the polypeptide chain could cause improper folding of the protein molecule making it non-functional.

Answer 2

A point mutation, or single base substitution, is a type of mutation that causes the replacement of a single base nucleotide with another nucleotide

For example, sickle-cell disease is caused by a single point mutation (a missense mutation) in the beta-hemoglobin gene that converts a GAG codon into GTG, which encodes the amino acid valine rather than glutamic acid.