Mutation

In order for us to evolve, mutation of our genes is necessary. However, not all of these mutations are beneficial. 

 Define gene mutation.
 A gene mutation is a change in the nucleotide sequence of a gene. 
 Since each new strand of DNA is proofread for errors by DNA Polymerase, it's rare that there is an error in replication. Apparently, the chance that the DNA is repicated incorrectly is about one in 1 billion replicated nucleotides. 

There are two types of mutations that are relevant to this section of coursework: Frameshift and Point mutations. 

A frameshift mutation is an error on the  'reading frame' or sequence of codons that are presented for replication. Since replication begins at a specific point ,when one codon is deleted, the results can be devastating since it shifts the entire row codons down one slot and turns the result into something that doesn't make sense. Imagine you deleted the first letter out of a sentence but kept the spacing the same.
'When is dinner ready?' turns into 'heni sdinne rready?". Nonsensical and it has lost its intended meaning. This is how frameshift mutations occur- by deleting or adding a nucleotide into DNA, rendering it nonfunctional.

A point mutation  happens anywhere along the gene and does not involve a deletion or addition but a change in a specific nucleotide.  

Remember our chart of codons. Each three letters actually stand for a specific amino acid. 61 of them are amino acids, two are Stop codons (describes where termination of synthesis occurs) and one is a Start codon. 

In most instances, replacing one base with another does not have a drastic effect. It can change one codon to another and through luck of the draw, the change results in the same kind of amino acid and life goes on (called a silent mutation)  for instance, CGC is arginine. Substitute CGG and the result is still arginine.
 
In some cases, the codon can be changed to become a stop codon, prematurely ending synthesis and resulting in a too short protein that is non functional (nonsense mutation). 
 
Other times, a missense mutation happens. This is when the meaning of the codon is changed completely when one amino acid is substituted. if CAC is incorporated into the protein instead of UAC, then histidine is added instead of tyrosine. This is disastrous especially since the polarity of the two differ.


Sickle Cell disease is caused by a missense mutation. 
Along the chain, Valine is substituted for Glutamate long the hemoglobin chain. This results in the sickling of the red blood cells and among other things, their premature breakdown-- causing anemia and other complications.