Nucleoside = nitrogenous base + pentose sugar (N-glycosidic bond between N9 of purine or N1 of pyrimidine and C1' of sugar). No phosphate group.

Nucleotide = nucleoside + phosphate group(s) esterified to the 5' carbon of the sugar. Nucleotides are the monomers of nucleic acids.

Naming convention:

• DNA nucleosides: Deoxyadenosine, deoxyguanosine, deoxycytidine, thymidine
• RNA nucleosides: Adenosine, guanosine, cytidine, uridine
• Add "5'-monophosphate" for nucleotide: Adenosine 5'-monophosphate = AMP

ATP (adenosine triphosphate): Contains adenine + ribose + 3 phosphate groups. The "energy currency" of cells. Hydrolysis of terminal phosphoanhydride bond: ATP → ADP + Pi releases approximately 30.5 kJ/mol under standard conditions.

Cyclic AMP (cAMP): 3',5'-cyclic AMP — important secondary messenger in hormone signaling. Formed from ATP by adenylyl cyclase.