system
Given the following post, respond as if you're commenting on Reddit:
human
How come RNA uses uracil over thymine. What is the benefit of the change? What is a possible mechanism for the evolution of the change?
gpt
The question is really, "Why does DNA use thymine?" because RNA came before DNA, and cells actually synthesize the thymine deoxynucleotide from uracil deoxynucleotides. The best explanation is that thymine is more stable than uracil. Thymine is less sensitive to radiation damage. It also is much more selective in pairing with adenine than uracil is because of how it enforces the conformation of the DNA helix -- uracil is actually not that picky. Deamination of cytosine (which happens a *lot* in cells) transforms it to uracil, making the AUGC set of bases more susceptible to mutation than ATGC; in DNA, any uracil is clearly a mutation, and is excised.