Biochemistry · Topic
Nucleotide structure !
A nucleotide is a nitrogenous base joined to a sugar and one or more phosphates; they build DNA and RNA and serve as the cell's energy currency.
Updated 2026-11-01
Key facts
- Nucleoside = base + sugar. Nucleotide = nucleoside + phosphate(s).
- Purines (two rings): adenine and guanine. Pyrimidines (one ring): cytosine, thymine (DNA) and uracil (RNA).
- RNA carries ribose (OH at C2'); DNA carries 2'-deoxyribose.
- In DNA, A pairs with T (2 hydrogen bonds) and G with C (3 bonds).
- Nucleotides are linked by 3'→5' phosphodiester bonds.
In detail
- The base joins C1' of the sugar by a β-N-glycosidic bond: through N9 in purines and N1 in pyrimidines.
- Names: adenine → adenosine → AMP/ADP/ATP; guanine → guanosine → GMP; hypoxanthine → inosine → IMP; uracil → uridine → UMP; thymine → thymidine → dTMP.
- The phosphates are named α, β and γ from the sugar; the β–γ and α–β bonds are high-energy.
- Besides building nucleic acids, nucleotides are coenzymes (NAD⁺, FAD, CoA), second messengers (cAMP, cGMP) and activated carriers (UDP-glucose, CDP-choline, SAM).
- Bases absorb ultraviolet light at 260 nm, which is how DNA and RNA are measured in the lab.
- Many drugs are nucleoside analogues (aciclovir, zidovudine, gemcitabine): the cell or virus phosphorylates them and mistakes them for its own.
Memory aid
«PURe As Gold»: PURines are A and G. «CUT the PY(e)»: pyrimidines are C, U and T.
Clinical notes
- Uric acid is the end of purines; pyrimidines break down to soluble products (β-alanine, β-aminoisobutyrate), without crystals.
- Base and nucleoside analogues underlie many antivirals, anticancer drugs and immunosuppressants.
Pathways
Related
- ATP (adenosine triphosphate)
- NAD⁺ (nicotinamide adenine dinucleotide)
- IMP (inosine monophosphate)
- dTMP (thymidine monophosphate)
- PRPP (phosphoribosyl pyrophosphate)
- Drugs acting on nucleotide metabolism
- Ribonucleotide reductase
Test yourself
Think of the answer, then tap the question to see it.
What is the difference between a nucleoside and a nucleotide?
A nucleoside is base + sugar; a nucleotide adds one or more phosphates.
Why is the G–C pair more stable than A–T?
G and C form three hydrogen bonds; A and T only two.
Which sugar group distinguishes RNA from DNA?
The 2'-OH of ribose, which DNA's deoxyribose lacks.
Through which atom do purines and pyrimidines attach to the sugar?
Purines through N9 and pyrimidines through N1, by a β-N-glycosidic bond.
Educational information, not medical advice. For any symptom, see a health professional.
Sources: Metabolism of nucleotides (Reactome, 2026); Inosinic Acid (CID 135398640) (PubChem, NCBI, 2026) · Public domain; Textbook of Biochemistry for Medical Students, 6th ed. (Jaypee Brothers Medical Publishers (Vasudevan DM, Sreekumari S, Vaidyanathan K), 2011).
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Representative model, for educational purposes only.