Purines vs Pyrimidines

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Purines and Pyrimidines are nitrogenous bases that make up the two different kinds of nucleotide bases in DNA and RNA. The two-carbon nitrogen ring bases (adenine and guanine) are purines, while the one-carbon nitrogen ring bases (thymine and cytosine) are pyrimidines.

Comparison chart

Purines versus Pyrimidines comparison chart
	Purines	Pyrimidines
Introduction (from Wikipedia)	A purine is a heterocyclic aromatic organic compound, consisting of a pyrimidine ring fused to an imidazole ring.	Pyrimidine is a heterocyclic aromatic organic compound similar to benzene and pyridine, containing two nitrogen atoms at positions 1 and 3 of the six-member ring. It is isomeric with two other forms of diazine.
Function	Production of RNA and DNA, proteins and starches, the regulation of enzymes and cell signaling.	Production of RNA and DNA, proteins and starches, the regulation of enzymes and cell signaling.
Nucleobases	Adenine and guanine	Cytosine, thymine, uracil
Structure	A pyrimidine ring fused to a imidazole ring. Contains two carbon-nitrogen rings and four nitrogen atoms.	Contains one carbon-nitrogen ring and two nitrogen atoms.
Melting point	214 °C, 487 K, 417 °F	20–22 °C
Type of Compound	Heterocyclic aromatic organic compound	Heterocyclic aromatic organic compound
Molecular formula	C5H4N4	C4H4N2
Molar mass	120.11 g mol−1	80.088 g mol-1
MeSH	Purine	Pyrimidine
SMILES	c1c2c(nc[nH]2)ncn1	C1=CN=CN=C1
CAS number	120-73-0	289-95-2 Y
PubChem	1044	9260
Synthesis in Lab	Traube Purine Synthesis	Biginelli Reaction

Structure

Purine (L) and Pyrimidine (R) molecules, where Black= Carbon, White=Hydrogen, Blue=Nitrogen

A purine is a heterocyclic aromatic organic compound containing 4 nitrogen atoms. It contains two carbon rings, and is made of a pyrimidine ring fused to an imidazole ring.

Structure of a purine

A pyrimidine is a heterocyclic aromatic organic compound containing 2 nitrogen atoms. It contains only one carbon ring.

Structure of a pyrimidine

Function

Both purines and pyrimidines have the same function: they serve as a form of energy for cells, and are essential for production of DNA and RNA, proteins, starch, regulations of enzymes, cell signaling.

Nucleobases

Purines make up two of the four nucleobases in DNA and RNA: adenine and guanine. Pyramidines make up the other bases in DNA and RNA: cytosine, thymine (in DNA) and uracil (in RNA). Useful mnemonics to remember these bases are:

"CUT the Py": CUT: Cytosine, Uracil, Thymine; Py (Pyrimindines)
"Pure As Gold (Pur AG)": Purines are Adenine, Guanine