Special enzymes remove damage in DNA Using bacterial DNA which, just like human DNA, consists of nucleotides with the bases adenine, guanine, cytosine, and thymine, Tomas Lindahl began to look for repair enzymes. One chemical weakness in DNA is that cytosine easily loses an amino group, which can lead to the alteration of genetic information. In DNA’s double helix, cytosine always pairs with guanine, but when the amino group disappears, the damaged remains tend to pair with adenine. Therefore, if this defect is allowed to persist, a mutation will occur the next time DNA is replicated. Lindahl realised that the cell must have some protection against this, and was able to identify a bacterial enzyme that removes damaged remains of cytosines from DNA. In 1974, he published his findings.
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