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signal peptide:
Short sequence of amino acids that determines the eventual location
of a protein in the cell. An example is the N-terminal sequence
of 20 or so amino acids that directs nascent secretory and transmembrane
proteins to the endoplasmic reticulum.
signal transduction:
Relaying of a signal by conversion from one physical or chemical
form to another. In cell biology, the process by which a cell
converts an extracellular signal into a response.
signaling molecule:
Extracellular or intracellular molecule that cues the response
of a cell to the behavior of other cells or objects in the environment.
sister chromatid:
see chromatid
Smart Materials and Products:
Materials and products capable of complex behavior due to the
incorporation of nanocomputers and nanomachines. Also used for
products able to respond to their environment.
smooth
endoplasmic reticulum (SER):
Region of the endoplasmic reticulum not associated with ribosomes;
involved in the synthesis of lipids.
smooth muscle:
Type of muscle found in the walls of arteries and of the intestine
and other viscera, and in some other locations of the vertebrate
body. Composed of long, spindle-shaped mononucleate cells. Called
”smooth” because it lacks the striations caused by the
sarcomeres in skeletal and cardiac muscle cells.
sodium
pump (Na+-K+ ATPase):
Transmembrane carrier protein found in the plasma membrane of
most animal cells that pumps Na+ out of and K+ into the cell,
using the energy derived from ATP hydrolysis.
Solute:
Any molecule that is dissolved in a liquid. The liquid is called
a solvent.
somatic cell:
Any cell of a plant or animal other than a germ cell or germ-cell
precursor. (From Greek soma, body.)
somite:
One of a series of paired blocks of mesoderm that form during
early development and lie on either side of the notochord in a
vertebrate embryo. They give rise to the vertebral column; each
somite produces the musculature of one vertebral segment, plus
associated connective tissue including that forming the vertebrae
to which that musculature is attached.
Southern blotting:
Technique in which DNA fragments, separated by electrophoresis,
are immobilized on a paper sheet; specific molecules are then
detected with a labeled nucleic acid probe. (After E.M. Southern,
inventor of the technique.)
Spemann’s
Organizer:
Specialized tissue at the dorsal tip of the blastopore in an amphibian
embryo; a source of signals that help to orchestrate formation
of the embryonic body axis. (After H. Spemann and H. Mangold,
co-discoverers.)
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