A Dalton (Da) is a unit of mass used in the field of chemistry and molecular biology to express the molecular weight or mass of atoms, molecules, and compounds. It is named after John Dalton, a British chemist and physicist who contributed to the development of modern atomic theory.
One Dalton (Da) is defined as one twelfth of the mass of an unbound carbon-12 atom, which is roughly equivalent to 1.66053906660 x 10^-27 kilograms. This definition was adopted as the standard for atomic mass units (u) and is now used internationally.
Daltons are useful in the following contexts:
Atomic and Molecular Mass: The molecular weight or mass of a molecule is often expressed in Daltons. For example, the molecular weight of water (H2O) is approximately 18.01528 Da, which means that one molecule of water has a mass of approximately 18.01528 Daltons.
Proteomics and Biochemistry: In biology, particularly in the study of proteins, the mass of biomolecules like proteins and nucleic acids is often measured in Daltons. This is important for understanding their structure and function.
Mass Spectrometry: Mass spectrometry is a powerful analytical technique used to determine the mass and composition of molecules. Mass spectrometry results are often reported in Daltons.
Chemical Reactions: In chemical reactions, the mass of reactants and products can be expressed in Daltons to understand the stoichiometry of the reaction.
A picogram (pg) is a metric unit of mass in the International System of Units (SI). It represents one trillionth of a gram or 10^-12 grams. The metric system is a decimal-based system of measurement used worldwide, and it is particularly useful for expressing extremely small quantities of mass.
To provide context for the size of a picogram:
Picograms are primarily used in scientific and technical fields, especially in situations where measuring minuscule quantities of substances or particles is essential. Some common applications of picograms include: