Cells are like small cities. They contain all the necessary parts that allow their infrastructure, function, growth, and communication to operate. For over a century scientists have been looking at the structures and organelles in cells using microscopic methods, and then drawing conclusions about their function. Biochemical methods have allowed scientists to examine the inner life of the cell, an organisational unit basic to all life. Now, they are clarifying its structures in detail: from mitochondria, the "factories" of cells, which create energy; to the endoplasmic reticulum, necessary for protein synthesis and metabolic processes; to the Golgi apparatus, responsible for lipid synthesis and producing important energy reserves for cell growth.
Now scientists led by Matthias Mann have specialised in identifying individual proteins in protein complexes. Proteins have various functions in a cell, from transport to mechanical support. As enzymes, they catalyse all kinds of metabolic processes. They are also important components of signal chains, like those which transmit information from the exterior of the cell to its nucleus. In this way, proteins also control the transcription of genetic information and the synthesis of new proteins that comes with it.
In this study, the proteome researchers looked at liver cells in mice. Using mass spectrometry, and by comparing databases, the scientists were able to detect more than 1400 proteins, localised in ten different cell compartments. Previous analyses had shown that certain proteins assign themselves clearly to particular cell organelles. When the scien