They read the methylation patterns of these cells using a chemical trick that turns methylated cytosine (letter C) into another base, called uracil.
(RNA, which is used in various intermediate stages by many organisms, and also by viruses, substitutes another molecule, uracil for thymine, but the two are very similar).The unnatural molecule is 3-fluorobenzene (3FB for short), which forms a pair with itself.
Triplets of this type are represented by one uracil (U) preceding, and adjacent to, two adenines (UAA) or preceding one adenine and one guanosine in either order (UGA, or UAG).
Each nucleic acid contains four of five possible nitrogen-containing bases: adenine (A), guanine (G), cytosine (C), thymine (T), and uracil (U).
The uracil in RNA has exactly the same hydrogen-bonding properties as thymine, so there are no changes at the information level.
In the most important nucleosides, the sugar is either ribose or deoxyribose, and the nitrogen-containing compound is either a pyrimidine (cytosine, thymine, or uracil) or a purine (adenine or guanine).
In addition, the pyrimidine base uracil, found in RNA, is replaced in DNA by thymine.
The major differences between 86] and [87] are that, in the latter, the nucleotides contain ribose instead of deoxyribose, and that, in RNA, uracil replaces the thymine of DNA.
Anions such as bisulfite can deaminate cytosine to form uracil, changing the genetic message by causing C-to-T transitions.
Halogens such as chlorine and bromine react directly with uracil, adenine, and guanine, giving substituted bases that are often mutagenic.
One of the two DNA strands is transcribed exactly into messenger RNA (mRNA), with the exception that the thymine base of DNA is replaced by uracil.
