n. [from the chemist John Dalton, proponent of the modern atomic theory of matter.] a unit of mass, approximately 1.66 x 10-24 grams; -- it is approximately equal to the mass of one hydrogen atom, but the exact value differs slightly as used in physics and chemistry. It is used mostly to describe the size of proteins and nucleic acids in biochemistry. Molecular weights are often expressed as dimensionless units, the unit being understood (in chemistry) to be the atomic mass unit with carbon equal to 14. Thus having a "molecular weight of 255" means the same as each molecule having a mass of 255 daltons.
Syn. atomic mass unit.


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