What is a kinase cascade?

A kinase cascade is a sequence of covalent modification cycles, in which the activated protein in one series promotes the activation of the protein in the next tier. More specifically, a kinase cascade is a series of reactions in which a signal is transmitted onto intracellular downstream proteins by protein phosphorylation and activation of cascade components. The activation of one kinase leads to the activation of downstream kinases. This results in the activation of specific effector molecules and downstream cellular responses. 

A kinase cascade can be initiated by various extracellular stimuli like cytokines, growth factors or hormones. These bind to specific cell surface receptors and activate intracellular signaling pathways. When they become activated, the receptor also activates a downstream kinase. This in turn activates another kinase, generating the cascade of kinase activity.