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point mutations
dna sequences
point mutation
living organisms
amino acids
base pair
Mutations Within Our Genetic Code
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Mutations are a very common occurrence within DNA sequences of all living organisms. It is the primary source of evolution, causing new alleles and traits to arise from within a species. In addition to aiding evolution and reproduction, mutations can cause detrimental effects, such as disease or disorder within an organism.

Point Mutations

Point mutations are one category of mutation. The first kind is known as a base substitution. This mutation occurs when one base pair is swapped out for another. These subsitutions can be further divided into the subcategories transition and transversion mutations. Transition mutations have purines, adenine and guanine, replaced by another purine, or the pyrimidines, cytosine and thymine, replaced by another pyrimidine. Transversion has a purine replaced by a pyrimidine, or a pyrimidines replaced by a purine.

The second type of point mutation actually contains two mutations, known as indel mutations. “Indel” is a portmanteau of insertion or deletion. True to its name, indel mutations will either insert or remove a base pair. This occurrence is also called a frameshift mutation. Because the nucleotides are shifted closer or further apart rather than replaced, it completely changes the shape and function of the resulting protein, which almost always results in proteins malfunctioning.

Functional Consequences

In addition to being categorized into point substitutions, both base substitution mutations and indel mutations are further divided into categories based on their side effects. Synonymous mutations are mutations where, even though the DNA has been mutated, the amino acid is still the same. This is due to the fact that the genetic code is redundant. These are also known as silent mutations.

The next mutation is known as a missense mutation. This is the opposite of a synonymous mutation, where animo acids in a protein chain are replaced with different amino acids, changing the shape and function of that protein. These mutations can result in a conservatice substitution, where the substituted amino acid is very similar to the original amino acid, only slightly changing the function of the protein. Nonconservative substitutions, on the other hand, greatly alter the function of the protein formed after translation. Missense mutations are also called nonsynonymous mutations.

The final mutation is called a nonsense mutation. This arises from an amino acid frame being changed into a stop codon when translated. These codons, UAA,UGA, and UAG, halt the translation process, resulting in proteins that are nowhere near the original shape and function once translation has been completed.

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