Proteomics is the branch of science that deals with the study of proteins, particularly their structures and functions. Proteins are important parts of living organisms, as they are the vital components of the physiological metabolic pathways of cells. Proteomics is the next step in the study of biological systems. It is more complicated than genomics because an organism's genome is more or less constant, whereas the proteome differs from cell to cell and from time to time. Distinct genes are expressed in different cell types, which mean that even the basic set of proteins that are produced in a cell needs to be identified. Proteomics has been defined as “the systematic analysis of the protein population in a tissue, cell, or subcellular compartment”.