are more than three K-40 half-lives old. In other words, these organisms existed when potassium had about eight times the radioactivity it does today. One might expect resistance to radiation-induced DNA damage to have been an even more important survival trait then, than today.
I can remember the first time I read a statement like this:
DNA undergoes major changes as a result of thermal fluctuations: for example, about 5000 purine bases (adenine and guanine) are lost every day from the DNA of each human cell because their N-glycosyl linkages to deoxyribose hydrolyze, a spontaneous reaction called depurination. Similarly, a spontaneous deamination of cytosine to uracil in DNA occurs at a rate of about 100 bases per cell per day (Figure 5-47).
I thought it was a little frightening to realilze how often such errors were generated; I had not known about DNA repair enzymes at the time.
The excerpt is from
this textbook; not one from which I learned what little biochemistry I know -- I used even older texts -- but one that might be worth acquiring. Just reading the little bit excerpted at the link added enormously to my awareness of the role of repair enzymes.
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