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[Biochemistry](https://durgical.com/en/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

- [De novo purine synthesis](https://durgical.com/en/biochemistry/pathways/de-novo-purine-synthesis/)
- [Pyrimidine synthesis](https://durgical.com/en/biochemistry/pathways/pyrimidine-synthesis/)

## Related

- [ATP (adenosine triphosphate)](https://durgical.com/en/biochemistry/molecules/atp/)
- [NAD⁺ (nicotinamide adenine dinucleotide)](https://durgical.com/en/biochemistry/molecules/nad/)
- [IMP (inosine monophosphate)](https://durgical.com/en/biochemistry/molecules/imp/)
- [dTMP (thymidine monophosphate)](https://durgical.com/en/biochemistry/molecules/dtmp/)
- [PRPP (phosphoribosyl pyrophosphate)](https://durgical.com/en/biochemistry/molecules/prpp/)
- [Drugs acting on nucleotide metabolism](https://durgical.com/en/biochemistry/topics/drugs-acting-on-nucleotide-metabolism/)
- [Ribonucleotide reductase](https://durgical.com/en/biochemistry/enzymes/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.

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Educational information, not medical advice. For any symptom, see a health professional.

Sources: [Metabolism of nucleotides](https://reactome.org/PathwayBrowser/#/R-HSA-15869) (Reactome, 2026); [Inosinic Acid (CID 135398640)](https://pubchem.ncbi.nlm.nih.gov/compound/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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