The central dogma of molecular biology puts proteins at the functional output stage of the flow of information. Thus, understanding which proteins are present and how they are regulated is instrumental to understanding any biological system.
Proteomics approaches can include detection and quantification of the proteins present and the specific posttranslational modifications (PTMs) at a certain cellular state, as well as the proteins coming together in specific organelles or in macromolecular protein complexes in certain stoichiometries.
Proteomics is a quite diverse field that can be partitioned into general and quantitative workflows. Quantitative proteomics is focused on determining the amount of protein or protein PTM in a sample, while more general workflows cover a broad area of protein mass spectrometry.