Kaffein on puriinirakenne kuten A ja G DNA.ssa

Wikipedia: 
Caffeine is a central nervous system (CNS) stimulant of the methylxanthine class of psychoactive drugs.^[9]
  It is the world's most widely consumed psychoactive drug, but unlike many other psychoactive substances, it is legal and unregulated in nearly all parts of the world.
It is a bitter, white crystalline purine, a methylxanthine alkaloid, and thus closely related chemically to the adenine and guanine contained in deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).
 It is found in the seeds, nuts, or leaves of a number of plants native to South America and East Asia.
The most well known source of caffeine is the seed (commonly incorrectly referred to as the "bean") of Coffea plants. Beverages containing caffeine are ingested to relieve or prevent drowsiness and to increase one's energy level.
 Caffeine is extracted from the plant part containing it for making beverages by steeping it in water, a process

Name	R1	R2	R3	R8	IUPAC nomenclature	Found In
Xanthine	H	H	H	H	3,7-dihydro-purine-2,6-dione	Plants, animals
Caffeine	CH3	CH3	CH3	H	1,3,7-trimethyl-1H-purine-2,6(3H,7H)-dione	Coffee, Guarana, Yerba mate, Tea, Kola, Guayusa, Holly
Theobromine	H	CH3	CH3	H	3,7-dihydro-3,7-dimethyl-1H-purine-2,6-dione	Cacao (chocolate), Yerba mate, Kola, Guayusa, Holly
Theophylline	CH3	CH3	H	H	1,3-dimethyl-7H-purine-2,6-dione	Tea, Cacao (chocolate), Yerba mate, Kola
Paraxanthine	CH3	H	CH3	H	1,7-dimethyl-7H-purine-2,6-dione	Animals that have consumed caffeine
8-Chlorotheophylline	CH3	CH3	H	Cl		Dimenhydrinate

See also

called infusion. These beverages are very popular; in North America, 90% of adults consume caffeine daily.