Pyrimidine molecules, including cytosine and thymine in DNA and cytosine and uracil in RNA, have a single ring structure and bind to purines to form DNA or RNA. Nucleosides and nucleotides consist of pyrimidines or purines, a sugar molecule, and a phosphate group. Fluorouracil, a pyrimidine-like drug, is used to treat skin cancer and other skin disorders.
Pyrimidine is a group of molecules that are part of the structure of DNA and RNA. These molecules exhibit a single ring structure made up of six atoms. There are several pyrimidine molecules, but only cytosine and thymine are part of the DNA structure, while cytosine and uracil are part of the RNA structure. These molecules bind to their purine counterparts to join the two strands of the DNA or RNA polymer. Pyrimidine-like drugs have been used to treat certain conditions, including skin cancer and keratosis.
Cytosine, thymine and uracil exhibit a six-membered ring structure. Uracil has two oxygen atoms attached to the ring. Cytosine has one oxygen atom and one amino group (-NH2) attached to the ring, while thymine has two oxygen atoms and one methyl group (-CH3) attached to the ring. The ring structure of each of these pyrimidine molecules contains two nitrogen atoms and four carbon atoms.
Pyrimidines bind to purines to join the two strands of the DNA or RNA polymer. Adenine and guanine are purines and each have a five-membered and a six-membered ring that are joined together. In DNA, cytosine binds to guanine and thymine binds to adenine. The connection between cytosine and guanine consists of three hydrogen bonds, while the connection between thymine and adenine has two hydrogen bonds. In RNA, uracil takes the place of thymine and binds to adenine.
When a sugar group is attached to a pyrimidine or purine, it is called a nucleoside. Deoxycytosine and (deoxy)thymidine are the pyrimidine nucleosides, and deoxyadenosine and deoxyguanosine are the purine nucleosides. In DNA, the sugar is deoxyribose, which is a five-carbon sugar molecule that lacks the hydroxyl group (-OH) normally found in the ribose sugar molecule. With RNA, the sugar molecule is ribose and nucleosides are usually named without the prefix “deoxy”.
A complete nucleotide consists of a nitrogenous base, which is pyrimidine or purine, a sugar molecule and a phosphate group. The phosphate group binds to the sugar molecule of a nucleoside through an ester bond. A nucleotide is linked to another nucleotide by a phosphodiester bond.
Fluorouracil is a drug similar in structure to pyrimidine uracil. It is usually used to treat a specific type of skin cancer called superficial basal cell carcinoma and other skin disorders, including scaly or crusted lesions caused by excessive sun exposure. The drug is usually sold in the form of a cream.
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