Ligand (biochemistry)

In biochemistry and pharmacology, a ligand is a substance that forms a complex with a biomolecule to serve a biological purpose. In protein-ligand binding, the ligand is usually a signal-triggering molecule binding to a site on a target protein. The binding typically results in a change of conformation of the target protein. In DNA-ligand binding studies, the ligand can be a small molecule, ion, or protein which binds to the DNA double helix.

The binding occurs by intermolecular forces, such as ionic bonds, hydrogen bonds and van der Waals forces. The association of docking is usually reversible through dissociation. Measurable irreversible covalent bonding between a ligand and target molecule is rare in biological systems. In contrast to the definition of ligand in metalorganic and inorganic chemistry, it is ambiguous whether the ligand typically binds at a metal site, as is the case in hemoglobin.

Ligand binding to a receptor (receptor protein) alters the chemical conformation (three-dimensional shape). The conformational state of a receptor protein determines the functional state. Ligands include substrates, inhibitors, activators, and neurotransmitters. The tendency or strength of binding is called affinity. Binding affinity is determined not only by host-guest interactions, but also by solvent effects that can play a dominant steric role in driving non-covalent binding in solution.

Affinity

Affinity may refer to:

Commerce, finance and law

Religion and belief

Science and technology

Johnny Alegre Affinity

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The Johnny Alegre AFFINITY is a jazz group originating from the Philippines. It is led by self-taught Philippine guitarist-composer Johnny Alegre, together with bassist Colby de la Calzada, drummer Koko Bermejo, pianist Elhmir Saison and saxophonist Tots Tolentino. The ensemble first gathered in May 2002 at Manila’s Pink Noise Studios for Alegre’s composition, “Stones of Intramuros”, for inclusion in the jazz anthology CD, Adobo Jazz Vol. 1, and thereafter carried on as a working unit.

The band’s first public appearance in October of the same year for the Adobo Jazz album launch at the Monk’s Dream Jazz Bar heralded the AFFINITY’s reputation –as described by aficionados in the ensuing reviews— as “Manila’s Jazz Superband”, with a power trio at its core. For the remainder of the year, the group emerged in various guises and personnel variations, manned by a who’s who of luminaries from the Philippine jazz scene.

Stargate SG-1 (season 8)

Season eight of Stargate SG-1, an American-Canadian military science fiction television series, began airing on July 9, 2004 on the Sci Fi channel. The eighth season concluded on February 22, 2005, after 20 episodes on British Sky One, which overtook the Sci Fi Channel in mid-season. This was the first season of the show to have 20 episodes instead of 22, as well as the first to air concurrently with Stargate SG-1 spinoff series Stargate Atlantis (the first season thereof). The series was originally developed by Brad Wright and Jonathan Glassner, while Brad Wright and Robert C. Cooper served as executive producers. Season eight regular cast members include Richard Dean Anderson, Amanda Tapping, Christopher Judge, and Michael Shanks. The eighth season begins with the SG-1 team trying to revive Colonel Jack O'Neill (Richard Dean Anderson) after the events of the seventh season. At the end of the two-episode season opener, Colonel O'Neill is promoted to General and assumes command of Stargate Command (SGC), while Major Samantha Carter (Amanda Tapping) is promoted to Lieutenant Colonel and assumes command of SG-1. The season arc centers on the growing threat and seemingly final defeat of the Goa'uld and the Replicators, races who were introduced in the first and third season of the show, respectively.