Proteome

The proteome is every protein present in a biological sample, whether a single cell type, an organ such as the liver, a body fluid like blood plasma or a whole organism. The word, a blend of protein and genome, was coined in 1994 by Marc Wilkins, and the field that studies them is proteomics.

Unlike the genome, which is nearly the same in every cell of the body, the proteome differs between cell types and changes over time with development, diet, disease and stress. It is also much more complex than the list of genes suggests. Humans have roughly 20,000 protein-coding genes, but alternative splicing and post-translational modifications such as phosphorylation, glycosylation and cleavage turn these into many more distinct protein forms. Protein levels also do not simply follow mRNA levels, because each protein is made and broken down at its own rate.

Researchers map proteomes mainly with mass spectrometry, often after separating proteins by two-dimensional gel electrophoresis or liquid chromatography. Comparing the proteomes of healthy and diseased tissue helps find biomarkers, measurable signs of disease, and drug targets, since most medicines act on proteins.