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A mitogen is any substance that triggers the process of mitosis, or cell division. Frequently, mitogens are proteins — compounds consisting of amino acid molecules that facilitate biochemical reactions in organisms. Mitogens are often encountered in the field of immunology due to their importance in inducing signal transduction pathways. These pathways are processes in an organism by which biochemical “signals” are passed from outside a cell to inside it, causing an alteration to take place within the cell. One such pathway, the mitogen-activated protein kinase (MAPK), can sometimes mutate and lead to cancer.
When a cell undergoes mitosis, it divides into two daughter cells that are identical to each other. In a series of phases, the cell splits so that one copy of genetic material is given to each daughter cell, along with about half the parent cell’s cytoplasm – the fluid inside the cell. The process of mitosis allows a cell to replicate itself. A mitogen operates by interacting with the cell membrane, the envelope surrounding the cell, and stimulating a reaction which leads to mitosis.
In immunology, mitogens can be used to stimulate mitosis of lymphocytes, or white blood cells — cells that protect the host organism from invading bacteria or viruses. The mitotic ability of lymphocytes can be used as a test to determine whether the immune system is functioning correctly. If a mitogen is introduced and the lymphocytes fail to respond by dividing, the immune system is considered to be impaired.
Mitogens also have importance in signal transduction pathways that mediate cell division, including the MAPK pathway. When a mitogen in the extracellular environment binds to a receptor element on the cell membrane, the chemical change it causes triggers activity in other molecules within the cell. The interaction of these molecules and proteins create a chain of signals that eventually produces MAPK, a protein that facilitates cell division and other processes.
If a component of the signal transduction pathway is mutated — for example, if one of the proteins is malformed — the pathway may have adverse consequences for the organism. The MAPK pathway, for instance, is thought to be a factor in the development of cancer. Cancers proliferate at an uncontrolled rate, creating a tumor that affects other tissues in the body. A malfunctioning protein in the MAPK pathway could cause the pathway to stimulate cell division in an uncontrolled manner, without shutting down, leading to tumor development.