Mitogen-activated protein kinase (MAPK) is a type of enzyme that plays a crucial role in transmitting signals within cells. It is part of a signaling pathway that helps cells respond to various external stimuli, such as growth factors, stress, and inflammation. By activating specific proteins, MAPK influences important cellular processes like growth, differentiation, and survival. MAPK pathways are essential for regulating many biological functions, including cell division and apoptosis (programmed cell death). There are several types of MAPKs, including extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and p38 MAPK, each with distinct roles in cellular responses and functions.