Cell Signalling developed when single cells evolved into multicellular organisms, there was a need for efficient communication between specialized cells.1 Cell signalling is important in homeostasis, the maintenance of an organism’s internal environment – cells are coordinated in tissue repair,tissue development and transfer of substances. The surface of the cell membrane contains embedded proteins and polysaccharides that bind to the extracellular matrix of another cell to mutually work together.
There are many different types of cell signalling: juxtacrine, paracrine and endocrine. In juxtacrine signalling, cells communicate directly with each other by cell-cell contact, or fusing their cytoplasm’s together to form a ‘gap junction’. A defining feature of juxtacrine signaling is ‘notch signaling’ where one cell overproduces a specific protein, which then frequently binds to the receptors on the other cell to cause a feedback loop system. Paracrine signalling travels over short distances, and uses hormones to send a signal to nearby cells. Endocrine signalling occurs over large distances in the organism, it involves the use of hormones as well. The hormones travel in the blood to target specific areas, e.g. follicle-stimulating hormone (FSH) travels from the pituitary gland to the female reproductive system.
Receptors and receptor ligand interactions fuel cell signalling. Ligands are neurotransmitters, hormones, any molecules that bind to receptors in the membrane to send a signal. After a signal has been sent, the ligands are usually recycled in gap junctions so the ongoing signal is halted. Many diseases and conditions in organisms develop due to problems in cell signaling, e.g. problems in serotonin transmission are linked to depression.
1. Cell. (n.d.). In Encyclopedia Britannica online. Retrieved from http://www.britannica.com/EBchecked/topic/101396/cell/37429/Intermediate-filaments#toc37431