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Thymine (/ ˈ θ aɪ m ɪ n /) (symbol T or Thy) is one of the four nucleotide bases in the nucleic acid of DNA that are represented by the letters G–C–A–T. The others are adenine, guanine, and cytosine. Thymine is also known as 5-methyluracil, a pyrimidine nucleobase. In RNA, thymine is replaced by the nucleobase uracil.
The purine nitrogenous bases are characterized by their single amino group (−NH 2), at the C6 carbon in adenine and C2 in guanine. [5] Similarly, the simple-ring structure of cytosine, uracil, and thymine is derived of pyrimidine, so those three bases are called the pyrimidine bases. [6]
Uracil is also involved in the biosynthesis of polysaccharides and the transportation of sugars containing aldehydes. [22] Uracil is important for the detoxification of many carcinogens, for instance those found in tobacco smoke. [23] Uracil is also required to detoxify many drugs such as cannabinoids (THC) [24] and morphine (opioids). [25]
These symbols are also valid for RNA, except with U (uracil) replacing T (thymine). [1] Apart from adenine (A), cytosine (C), guanine (G), thymine (T) and uracil (U), DNA and RNA also contain bases that have been modified after the nucleic acid chain has been formed. In DNA, the most common modified base is 5-methylcytidine (m5C).
Methylation of cytosine to form 5-methylcytosine occurs at the same 5 position on the pyrimidine ring where the DNA base thymine's methyl group is located; the same position distinguishes thymine from the analogous RNA base uracil, which has no methyl group. Spontaneous deamination of 5-methylcytosine converts it to thymine. This results in a T ...
Methylated forms of the major bases are most common in DNA. In viral DNA, some bases may be hydroxymethylated or glucosylated. In RNA, minor or modified bases occur more frequently. Some examples include hypoxanthine, dihydrouracil, methylated forms of uracil, cytosine, and guanine, as well as modified nucleoside pseudouridine. [3]
Deoxythymidine is non-toxic and is part of one of the four nucleosides in DNA. It is a naturally occurring compound that exists in all living organisms and DNA viruses. Instead of thymidine, RNA contains uridine (uracil joined to ribose). Uracil is chemically very similar to thymine, which is also known as 5-methyluracil.
Nucleosides are glycosylamines that can be thought of as nucleotides without a phosphate group.A nucleoside consists simply of a nucleobase (also termed a nitrogenous base) and a five-carbon sugar (ribose or 2'-deoxyribose) whereas a nucleotide is composed of a nucleobase, a five-carbon sugar, and one or more phosphate groups.