Structural Genomics
The effort to determine the 3D structures of large numbers of proteins using both experimental techniques and computer simulation.

Subduction zone
A zone where rocks of an oceanic plate are forced to plunge below much thicker continental crust, along margins between adjoining plates. As the plate descends, it melts and is released into the magma below the earth’s crust. Such a zone is marked by volcanoes and earthquakes. See plate tectonics.

Sum Rule
The rule that states that the probability of the occurrence of mutually exclusive events is the sum of the probabilities of the individual events.

Supercoiled
The coiling of a covalently closed circular duplex DNA molecule upon itself so that it crossed its own axis.

Svedberg Coefficient Unit (S unit)
A measure for the rate at which particles sediment in a centrigugal field. S units are a measure of the relative size of a particle, rather than the absolute size.

Supernatant
The fluid lying above a precipitate in a centrifuge following the centrifugation of a suspension.

Suppressor Gene
A gene that can suppress the action of another gene.
Symbiosis
A relationship of mutual benefit between two organisms that live together.

Sympatric speciation
Speciation via populations with overlapping geographic ranges.