In biology, second messengers are low-weight diffusible molecules that are used in signal transduction to relay signals within a cell. They are synthesized or released by specific enzymatic reactions, usually as a result of an external signal that was received by a transmembrane receptor and pre-processed by other membrane-associated proteins. There are three basic types of second messenger molecules: Biology is a branch of science, dealing with the study of life. ... Schematic drawing of the effects of diffusion through a semipermeable membrane. ... In general, a molecule is the smallest particle of a pure chemical substance that still retains its composition and chemical properties. ... In biology, signal transduction is any process by which a cell converts one kind of signal or stimulus into another. ... Cells in culture, stained for keratin (red) and DNA (green). ... Ribbon diagram of the enzyme TIM. TIM is catalytically perfect, meaning its conversion rate is limited, or nearly limited to its substrate diffusion rate. ... Transmembrane receptors are integral membrane proteins, which reside and operate typically within a cells plasma membrane, but also in the membranes of some subcellular compartments and organelles. ... A membrane protein is a protein molecule that is attached to, or associated with the membrane of a cell or an organelle. ...

• Hydrophobic molecules like diacylglycerol, InsP₃ and phosphatidylinositols are membrane-associated and diffuse from the plasma membrane into the juxtamembrane space where they can reach and regulate membrane-associated effector proteins.
• Hydrophilic molecules are water-soluble molecules, like cAMP, cGMP, and Ca²⁺, that are located within the cytosol.
• gases, nitric oxide (NO) and carbon monoxide (CO), that can diffuse both through cytosol and across cellular membranes.

These intracellular messengers have some properties in common: Hydrophobe (from the Greek (hydros) water and (phobos) fear) in chemistry refers to the physical property of a molecule that is repelled by water. ... Diacylglycerol (DAG) is a second messenger molecule made by phospholipase C (a membrane-bound enzyme), together with inositol triphosphate. ... Inositol triphosphate (also commonly known as inositol trisphosphate or triphosphoinositol; abbreviated InsP3 or IP3), together with diacylglycerol, is a second messenger molecule used in signal transduction in biological cells. ... Phosphatidylinositol (PI), a phospholipid that is located in the plasma membrane. ... Drawing of a cell membrane A component of every biological cell, the cell membrane (or plasma membrane) is a thin and structured bilayer of phospholipid and protein molecules that envelopes the cell. ... Hydrophile, from the Greek (hydros) water and φιλια (philia) friendship, refers to a physical property of a molecule that can transiently bond with water (H2O) through hydrogen bonding. ... Structure of cAMP Cyclic adenosine monophosphate (cAMP, cyclic AMP or 3-5-cyclic adenosine monophosphate) is a molecule that is important in many biological processes; it is derived from adenosine triphosphate (ATP). ... Cyclic guanosine monophosphate (cGMP) is a second messenger derived from GTP. Cyclic guanosine monophosphate (cGMP) is a cyclic nucleotide derived from guanosine triphosphate (GTP). ... Calcium plays a vital role in the biochemistry of the cell, particularly in signal transduction pathways. ... ÃThe cytosol (as opposed fatty cytoplasm, which also includes the organelles) is the internal fluid of the cell, and a large part of cell metabolism occurs here. ... In biology, signal transduction is any process by which a cell converts one kind of signal or stimulus into another. ... Carbon monoxide, chemical formula CO, is a colorless, odorless, tasteless, flammable and highly toxic gas. ...

• They can be synthesized/released and broken down again in specific reactions by enzymes.
• Some (like Ca²⁺) can be stored in special organelles and quickly released when needed.
• Their production/release and destruction can be localized, enabling the cell to limit space and time of signal activity.

Schematic of typical animal cell, showing subcellular components. ...

External links

• Kimball, J. Second Messengers. URL accessed on February 10, 2006.