A phosphorylation cascade is organised from many signalling proteins controlled by kinases. A protein kinase is activated by phosphorylation which in turn phosphorylates the next protein kinase in a sequence and so on. As the signal is carried onwards it is amplified and sometimes can spread to other signalling pathways . An example of a phosphorylation cascade is triggered by RAS; a MAP Kinase signalling molecule. Once activated it relays a signal downstream by phosphorylating the protein kinases Raf, Mek and Erk. Raf recieves a signal directly from RAS which in turn phosphorylates and activates Mek, the phosphorylation of Mek can then activate the final kinase in the series Erk .