DNA mutations

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Types and effects of mutations

Mutation can be defines as an error in the DNA that is being inherited.Contrary to  popular belief mutations may have deleterious side effects, no effect, or positive side effects for an organism.

Mutations can be categorized into three categories based on their effect on the normal functioning of the cell.

1. Silent mutation:if a mutation happens in introns (non coding part of the DNA) it is known as silent mutation.Introns are cut out of mRNA during processing. A mutation can also be silenced due to the redundant nature of the genetic code. In genetic code more than one codon code for the same amino acid. If the mutation happens and the resulting codon codes for the same amino acids then that mutation is silenced. For example, if a mutation happens on the third nucleotide of UUU, because which it changes to UUC it will not change the amino acid in the polypeptide that is being produced from this mRNA. This is due to the fact that UUU and UUC code for the amino acid Phenyl alanine.

Illustration of a silent mutation.

Silent mutation

2. Mis sense mutation:If a mutations results in change of a single amino acid in the polypeptide chain, it is known as mis sense mutation.Mis sense mutation can happen anywhere in the DNA and in any nucleotide of the codon.

Missense mutation

As you can see from above illustration, change of 4th nucleotide from G to C results in change of amino acid from Valine to leucine. Change of a single nucleotide may result in production of a polypeptide which is non functional.

3.Non sense mutation:When a mutation results in formation of a stop codon it is known as non sense mutation.There are three stop codons in the genetic code UAA,UAG and UGA. The process of making a polypeptide chain stops when the translation machiney reaches a stop codon.

non sense mutation

 


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