GENE MUTATIONS Mutations can happen during DNA replication or recombination; these are permanent. Most genes are completely harmless. Some will lead to cell death, cancer formation, or the production of an abnormal protein. Most of the dangerous complications come when DNA cannot be normally repaired as is the case with certain diseases. There are three major types of DNA mutations that can be seen. Point mutations involve base substitutions. Sickle cell disease stems from a single point mutation in which glutamine is substituted by valine in the making of a hemoglobin molecule. These types of mutations are the most common. There are two types of point mutations. One is called a transition mutation, in which a purine is substituted for another purine base or a pyrimidine is substituted for another pyrimidine base. The other is called a transversion mutation, in which pyrimidines are substituted for purines, or vice versa. Point mutations can also be silent, missense, or nonsense mutations. Silent mutations result in the same amino acid being created. Missense mutations happen when a different amino acid gets made so there is a different protein sequence. The different sequence can be conservative and will have the same basic properties or can be nonconservative, with different properties. Nonsense mutations results in a stop codon being transcribed so there is a shorter protein that isn’t functional. Deletions can result in a frameshift mutation, which is more severe than a point mutation. Frameshift mutations happen when one or two bases are deleted so that the codons after it are completely garbled. The end-product message is completely garbled and nonfunctional. If three bases are deleted, just one amino acid is missing, which is actually better than if one or two bases are deleted. Insertions behave the same way so that, if it occurs in clusters of three base pairs, it isn’t as serious as will be seen if one or two base pairs are inserted. Sometimes, there can be a noncomplementary base incorporated into a daughter strand. This leads to a mutation after the next round of replication. This is very rare because there are enzymes acting in the proofreading process will correct the problem before it
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