In cell biology, mitogen-activated protein kinases (MAPKs) (EC 2.7.1.37) are serine/threonine-specific protein kinases that respond to extracellular stimuli (mitogens) and regulate various cellular activities, such as gene expression, mitosis, differentiation, and cell survival/apoptosis. Extracellular stimuli lead to activation of a MAPK via a signaling cascade composed of MAPK, MAPK kinase (MAPKK), and MAPKK kinase (MAPKKK). A MAPKKK that is activated by extracellular stimuli phosphorylates a MAPKK on its serine and threonine residues, and then this MAPKK activates a MAPK through phosphorylation on its serine and tyrosine residues. This MAPK signaling cascade has been evolutionarily well-conserved from yeast to mammals. Cell biology (also called cellular biology or cytology, from the Greek kytos, container) is an academic discipline which studies cells. ... EC numbers (Enzyme Commission numbers) are a numerical classification scheme for enzymes, based on the chemical reactions they catalyze. ... Serine is one of the 20 most common natural amino acids on Earth. ... Threonine is one of the 20 most common natural amino acids on Earth. ... A protein kinase is an enzyme that can transfer a phosphate group from a donor molecule (usually ATP) to an amino acid residue of a protein. ... A mitogen is a substance that causes a cell to begin dividing. ... Gene expression (also protein expression or often simply expression) is the process by which a genes information is converted into the structures and functions of a cell. ... Light micrograph of a newt lung cell in early anaphase of mitosis. ... Cellular differentiation is a concept from developmental biology describing the process by which cells acquire a type. The morphology of a cell may change dramatically during differentiation, but the genetic material remains the same, with few exceptions. ... In biology, apoptosis (from the Greek words apo = from and ptosis = falling, pronounced ap-a-tow-sis[1]) is one of the main types of programmed cell death (PCD). ... The word cascade can have many meanings: In biochemistry, a cascade is a consecutive series of chemical reactions. ... Phosphorylation is the addition of a phosphate (PO4) group to a protein or a small molecule. ... Tyrosine (from the Greek tyros, meaning cheese, as it was first discovered in cheese), 4-hydroxyphenylalanine, or 2-amino-3(4-hydroxyphenyl)-propanoic acid, is one of the 20 amino acids that are used by cells to synthesize proteins. ... Yeasts constitute a group of single-celled (unicellular) fungi, a few species of which are commonly used to leaven bread and ferment alcoholic beverages. ... Orders Subclass Monotremata Monotremata Subclass Marsupialia Didelphimorphia Paucituberculata Microbiotheria Dasyuromorphia Peramelemorphia Notoryctemorphia Diprotodontia Subclass Placentalia Xenarthra Dermoptera Desmostylia Scandentia Primates Rodentia Lagomorpha Insectivora Chiroptera Pholidota Carnivora Perissodactyla Artiodactyla Cetacea Afrosoricida Macroscelidea Tubulidentata Hyracoidea Proboscidea Sirenia The mammals are the class of vertebrate animals primarily characterized by the presence of mammary...

To date, four distinct groups of MAPKs have been characterized in mammals: (1) extracellular signal-regulated kinases (ERKs), (2) c-Jun N-terminal kinases (JNKs), (3) p38 isoforms, and (4) ERK5. The ERKs (also known as classical MAPKs) signaling pathway is preferentially activated in response to growth factors and phorbol ester (a tumor promoter), and regulates cell proliferation and cell differentiation. The JNKs (also known as stress-activated protein kinases; SAPKs) and p38 signaling pathways are responsive to stress stimuli, such as cytokines, ultraviolet irradiation, heat shock, and osmotic shock, and are involved in cell differentiation and apoptosis. And ERK5, which has been found recently, is activated both by growth factors and by stress stimuli, and it participates in cell proliferation. Growth factor is any of about twenty small proteins that attach to specific receptors on the surface of stem cells in bone marrow and promote differentiation and maturation of these cells into morphotic constituents of blood. ... Cytokines are small protein molecules that are the core of communication between immune system cells, and even between immune system cells and cells belonging to other tissue types. ... Ultraviolet (UV) radiation is electromagnetic radiation of a wavelength shorter than that of the visible region, but longer than that of soft X-rays. ...