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|Chapter Six: DNA, RNA, and Protein Synthesis|
A mutation is a change in the DNA of an organism. Most mutations are harmful, but because of the redundancy of DNA (that certain codes are repeated over and over), a mutation in a single area may have only a minimal effect. We will discuss the two main types of mutations: point mutations and frame shift mutations.
A point mutation is very easy to understand. It simply means that one base is replaced with another. For example, if a part of the DNA should read TAC GGA ACT ATG but instead reads TAC GCA ATT ATG, then a point mutation has occurred in the third codon. Notice that all of the other codons remained the same. So if this part of the DNA were transcribed into mRNA which was later translated into a protein molecule, only one amino acid would be different than usual since only one codon was changed. Usually, a protein with only one amino acid different can still function normally.
By contrast to this minor effect, frame shift mutations can have much more serious consequences. A frame shift mutation occurs when a base is either added or deleted from the DNA sequence. Taking the example from before, suppose that a nucleotide with thymine was added in the second codon so that the sequence becomes TAC GGCA ACT ATG. Since the codons are triplets, this would actually be read as TAC GGC AAC TAT G... The first codon is the same, but all of the other ones are completely different, so the protein produced would also be very different from what it should be. Usually, the resulting protein will not be able to perform the function that the original one was meant to do. This is why frame shift mutations have far more severe effects than do point mutations.