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Saccharomyces cerevisiae Brewer's yeast, familiar to cooks as the yeast used to leaven bread, was the first and is still the most widely used yeast species in biotechnology. Certain strains are used in the manufacture of alcoholic beverages and fermented foods—and also for expression of genes. Biologically active interferons, for example, have been produced in it and it can be used in the manufacture of biologics. Commonly abbreviated: S. cerevisiae.

scale-down To model a biopharmaceutical manufacturing process (or section of that process) at the laboratory scale, usually for validation or other study purposes. Scale-down requires holding the critical parameters constant, and may be confounded by differences in equipment dead volumes, performance, or materials of construction.

Schizosaccharomyces pombe The second most commonly used yeast species in biotechnology, originally used in east Africa to brew millet beer, but which is typically unsuitable for other types of fermentation because of the large amount of sulfurous compounds it emits.

SDMS Scientific Data Management System; an automated, electronic repository that stores and manages all types of scientific data to a centralized database, offering integration with a multitude of research applications.

SDS Sodium dodecylsulfate; an ionic detergent that binds to and denatures proteins, and binds in rough proportion to the size of the protein; used to aid analytical separations.

SDS-PAGE Sodium dodecyl sulfate-polyacrylamide gel electrophoresis the SDS detergent denatures and binds to proteins, aiding in their separation. Analytical separation technique, often used to characterize proteins or mixtures, that uses a charged gel environment through which molecules of varying sizes and electric charges migrate from one pole to the other. Unlike gel-filtration chromatography, larger molecules move more slowly than smaller molecules because migration rate is not dependent on diffusion into and out of particles.

SEC Size-exclusion chromatography, gel-filtration or gel-permeation chromatography. An analytical method that uses porous particles to separate molecules of different sizes. Molecules that are smaller than the pore size can enter the particles and therefore have a longer path and longer transit time than larger molecules that cannot enter the particles. SEC can separate biological molecules and help scientists determine the molecular weights and molecular weight distributions of polymers.

secondary structure In proteins, the folding, twisting, coiled, sometimes springlike chain that results when hydrogen bonds form between the adjacent parts of a molecule, as in an alpha helix or beta sheet.

seed stock The initial inoculum or the cells placed in growth medium from which other cells will grow.

sequence The precise order of bases in a nucleic acid or amino acids in a protein.

Ser Serine; one of more than 20 naturally occurring amino acids.

serum The watery portion of an animal or plant fluid (such as blood) remaining after coagulation. When cheese is made, whey is the milk serum that's left.

shear Tearing force (to cells), such as that caused by blending or stirring.

shelf life The period of time during which a drug can be stored without decreasing in quality, safety, or efficacy.

sialylated oligosaccharides Oligosac-charides that contain sialic acid (N-acetyl) neuramic acid are sialylated). Sialic acid is often found as a terminal residue of oligo-saccharide chains of glycoproteins. Sialic acid imparts negative charge to glycoproteins, because its carboxyl group tends to dissociate a proton at physiological pH.