Where does the unit Dalton come from when calculating atomic mass?

What Is the Dalton (Da)?

The Dalton (Da) is a unit of mass commonly used in biochemistry, molecular biology, and structural biology to express the mass of atoms, molecules, and subatomic particles. You may have noticed the Dalton often appears alongside or instead of the atomic mass unit (amu), especially in molecular weight calculations of proteins and biomolecules.

But where does this unit originate from, and how does it relate to atomic mass calculations?

Origin of the Dalton

The Dalton is named after John Dalton (1766–1844), a pioneering English chemist, physicist, and meteorologist who is widely regarded as the father of modern atomic theory.

Dalton proposed that:

• All matter is made up of indivisible atoms.
• Each element consists of identical atoms, and atoms of different elements have different weights.

His revolutionary atomic theory (1808) laid the groundwork for modern chemistry, introducing the idea that chemical reactions involve rearrangements of atoms, not their destruction or creation.

Definition of the Dalton

In modern scientific usage:

1 Dalton (Da) = 1 unified atomic mass unit (u) = 1/12 the mass of a carbon-12 atom.

Numerically:

1 Da = 1 u = 1.66053906660 × 10⁻²⁴ grams

This definition makes the Dalton synonymous with the atomic mass unit (amu).

Dalton vs. Atomic Mass Unit (amu): Are They the Same?

Why the Dalton Became Popular in Biology

In chemistry and physics, scientists traditionally used amu or unified atomic mass unit (u).

However, in biological sciences, researchers work with much larger molecules—like proteins, DNA strands, enzymes—that often exceed thousands or millions of amu.

To simplify communication:

• Dalton (Da) was introduced to express molecular weights more intuitively.
• For example, instead of writing 66,000 amu, biochemists simply write 66 kDa (kilodaltons).

Examples of Dalton Usage in Biology

This makes the Dalton a practical unit when discussing macromolecular structures.

Importance of Dalton in Scientific Research

• Protein Structure Studies: Molecular weights of proteins are almost always reported in Daltons.
• Mass Spectrometry: Output charts label peaks in Da/kDa.
• Genetic Research: DNA sequences are measured using Daltons to estimate mass of fragments.
• Pharmaceutical Industry: Drug molecules are described in Daltons for dosage and efficacy studies.

Dalton in International Scientific Standards

The Dalton is an accepted non-SI unit, but its use is sanctioned by IUPAC and IUBMB (International Union of Biochemistry and Molecular Biology).

The term is officially included in scientific literature because:

• It offers clarity in biological sciences.
• It aligns seamlessly with the atomic mass unit (amu/u).

The Dalton (Da) comes from the historical legacy of John Dalton, who introduced atomic theory to science. Over time, the Dalton became synonymous with the atomic mass unit, offering biological sciences a practical and readable way to express molecular masses. Whether you’re a chemist, physicist, or biologist, understanding the Dalton bridges the gap between atomic theory and biological applications.