In the past 15 years, scientists have discovered more of the code the cells use for their internal communications. Signal transmission begins when a messenger "docks" temporarily with a specific receptor on a recipient cell. This receptor is physically connected to the cytoplasm, and because of this is able to relay a message. The receptor is usually a protein that includes three domains: an external docking region for the messenger, a component that spans the cell's outer membrane, and a tail that extends into the cytoplasm. When the messenger binds to the external site, it generates a change in the shape of the tail. This eases the tail's interactions with the information-relaying molecules in the cytoplasm, which lead to more cellular signaling.

Kinases and phosphatases control most activities in cells. If one kinase activates a protein, a phosphatase will be charged with inactivating that protein, or vice versa. Human cells will manufacture hundreds of different kinases and phosphatases. Scaffolding proteins seem to be a common strategy for preventing the wrong kinases and phosphatases from acting on a target; they create the proper reactions by holding selected kinases and phosphatases near the precise proteins they are supposed to maintain.

Even when a full protein is formed from nothing but protein-binding modules, it can function as an indispensable adapter. One module plugs into a developing signaling complex, and the other modules allow more proteins to join the network. The adapters enable cells to make use of enzymes that otherwise might not fit into a particular signaling circuit.

Knowledge of the time held that the messages were transmitted within cells primarily through enzymatic reactions, where one molecule alters a second without tightly binding to it and without being distorted. The receptors did not necessarily alter the chemistry of the SH2-containing proteins. Many merely stimulated the SH2 domains to latch onto the phosphate-decorated tyrosines.

Studies of receptor tyrosine kinases and of SH2 domains have also helped clarify how cells guarantee that only the precise proteins combine to form any chosen signaling pathway. Diverse hormones and receptors produce different effects on the cells. SH2 domains have been found to be present in over 100 separate proteins. Every SH2 domain includes a region that fits securely over a phosphate-bearing tyrosine, as well as a second region. These regions differ from one SH2 domain to another, and the region recognizes a particular sequence of three or so amino acids next to the phosphate-bearing tyrosine, or phosphotyrosine. For this reason, all SH2 domains can bind to phosphorylated tyrosine, but

Some common words found in the essay are:
Communication Physiology, sh2 domain, kinases phosphatases, receptor tyrosine kinases, amino acids, sh2 domains, receptor tyrosine, tyrosine kinases, human body, adapter proteins, impulse produced, sh2-containing proteins,
Approximate Word count = 1321
Approximate Pages = 5 (250 words per page double spaced)