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Short answer
A nucleotide is the basic building block of nucleic acids. Each one has a sugar, a phosphate group and a nitrogen-containing base, and DNA is a long chain of these units. In DNA the sugar is deoxyribose and the bases are adenine (A), cytosine (C), guanine (G) and thymine (T). RNA is built from nucleotides too, with ribose and uracil (U) in place of thymine.
Definition and scope
This guide explains how nucleotides relate to DNA and RNA, using the NHGRI Talking Glossary as its source. It covers terminology, not bench procedure. The NHGRI glossary defines a nucleotide as “the basic building block of nucleic acids (RNA and DNA)”, made of a sugar molecule attached to a phosphate group and a nitrogen-containing base. It describes DNA and RNA molecules as polymers made up of long chains of nucleotides, and says the information content of those molecules is encoded in the chains.
The search variants “nucleotide and DNA”, “nucleotide for DNA”, “nucleotide on DNA” and “nucleotides on DNA” all point at the same relationship. The nucleotide is the unit and DNA is the polymer built from it. DNA is not something a nucleotide sits on top of; the nucleotides are the molecule.
How nucleotides build DNA
Per the NHGRI definitions, each nucleotide contributes one sugar, one phosphate group and one base. In DNA the sugar is deoxyribose, and the base is one of A, C, G or T. A DNA strand is a chain of these units, and the order of the bases carries the genetic information.
NHGRI describes DNA as the molecule that carries genetic information, with two strands joined by specific links between bases: A pairs with T and C pairs with G. The twisted-ladder shape is the “double helix”.
Nucleotide, base, base pair and nucleic acid: a terminology ladder
Most confusion behind the query variants comes from using four related words as if they were one. Reading from smallest to largest, using NHGRI’s own definitions:
- Base. The nitrogen-containing part of a nucleotide: A, C, G and T in DNA; A, C, G and U in RNA.
- Nucleotide. The full unit: sugar plus phosphate group plus base.
- Base pair. Per NHGRI, “two complementary DNA nucleotide bases that pair together to form a ‘rung of the DNA ladder.'” The two strands are held together by hydrogen bonds between pairs of bases.
- Nucleic acid. The long chain, either DNA or RNA, made of many nucleotides.
So “a nucleotide” is one unit with all three parts, “a base” is only one part of that unit, and “a base pair” is two bases from opposite strands.
DNA vs RNA vs a single nucleotide
The table sets out the comparison readers usually come for (“difference between DNA and RNA”, “RNA structure”, “nucleotide for RNA”). Every cell comes from the NHGRI glossary pages listed under Sources.
| Feature | Single nucleotide | DNA | RNA |
|---|---|---|---|
| What it is | Basic building block of nucleic acids | Molecule that carries genetic information; a polymer of nucleotides | Nucleic acid present in all living cells; a polymer of nucleotides |
| Sugar | Ribose or deoxyribose | Deoxyribose | Ribose |
| Bases | One nitrogen-containing base per unit | A, C, G, T | A, C, G, U |
| Strands | Not applicable | Two strands; A pairs with T, C pairs with G | Most often single-stranded |
| Examples of types or roles | Not applicable | Carries genetic information | mRNA, rRNA and tRNA; some RNAs help regulate gene expression |
Where it matters for labs
The vocabulary above is the foundation for several bench topics, and the CASRAI guides below cover each in its own right. Because DNA and RNA differ in sugar and bases, CASRAI covers them in separate protocol guides: DNA extraction protocol basics and RNA extraction protocol basics. Reading nucleic acid concentration with light is covered in spectrophotometer for DNA concentration, and checking RNA on a gel in RNA in agarose gel. For the difference between a plasmid and chromosomal DNA, see plasmid DNA vs genomic DNA. For the broader field, see what is molecular biology.
Common misunderstandings
“A nucleotide is the same as a base.”
No. The base is one of the three parts of a nucleotide. The nucleotide also includes the sugar and the phosphate group.
“A nucleotide sits on DNA.”
Nucleotides are the units DNA is made of. The phrases “nucleotide on DNA” and “nucleotide for DNA” are usually shorthand for “a nucleotide in a DNA strand” or “the nucleotide building blocks of DNA”.
“RNA has the same bases as DNA.”
Three of the four are shared (A, C, G). RNA uses uracil where DNA uses thymine.
“RNA is always a double helix.”
NHGRI states that, unlike DNA, RNA is most often single-stranded.
FAQ
What are the nucleotides in DNA?
DNA nucleotides have deoxyribose as the sugar, a phosphate group, and one of four bases: adenine, cytosine, guanine or thymine.
What is the difference between DNA and RNA?
Per NHGRI, RNA has ribose and uracil where DNA has deoxyribose and thymine, and RNA is most often single-stranded while DNA has two strands joined by A-T and C-G base links.
What is a nucleotide for RNA?
An RNA nucleotide is a ribose sugar, a phosphate group and one of the bases A, C, G or U.
Which bases pair in DNA?
Adenine pairs with thymine, and cytosine pairs with guanine, held together by hydrogen bonds.
What is RNA structure like?
RNA is a chain of nucleotides, most often single-stranded. NHGRI lists mRNA, rRNA and tRNA as types, and notes that some RNAs help regulate gene expression.
Sources
- NHGRI Talking Glossary, Nucleotide, checked 2026-10-29.
- NHGRI Talking Glossary, Deoxyribonucleic acid, checked 2026-10-29.
- NHGRI Talking Glossary, RNA (ribonucleic acid), checked 2026-10-29.
- NHGRI Talking Glossary, Base pair, checked 2026-10-29.
