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S phase:
Period of a eucaryotic cell cycle in which DNA is synthesized.
Saccharomyces:
Genus of yeasts that reproduce asexually by budding or sexually
by conjugation. Economically important in brewing and baking,
they are also widely used in genetic engineering and as simple
model organisms in the study of eucaryotic cell biology.
Salmonella:
Rod-shaped, motile, aerobic genus of bacteria. Includes species
that cause food poisoning.
sarcoma:
Cancer of connective tissue.
sarcomere:
Repeating unit of a myofibril in a muscle cell, composed of an
array of overlapping thick (myosin) and thin (actin) filaments
between two adjacent Z discs.
sarcoplasmic reticulum:
Network of internal membranes in the cytoplasm of a muscle cell
that contains high concentrations of sequestered Ca2+
that is released into the cytosol during muscle excitation.
satellite DNA:
Regions of highly repetitive DNA from a eucaryotic chromosome,
usually identifiable by its unusual nucleotide composition. Satellite
DNA is not transcribed and has no known function.
saturated molecule:
Molecule containing carbon-carbon bonds that has only single covalent
bonds.
Scanning Tunneling Microscope (STM):
An instrument able to image
conducting surfaces to atomic accuracy; has been used to pin
molecules to a surface.
Schwann cell:
Glial cell responsible for forming myelin sheaths in the peripheral
nervous system.
second messenger:
Small molecule that is formed in or released into the cytosol
in response to an extracellular signal and helps to relay the
signal to the interior of the cell. Examples include cAMP, IP3
and Ca2+.
secondary structure:
Regular local folding pattern of a polymeric molecule; in proteins,
a helices and b-pleated
sheets.
secretory vesicle:
Membrane-bounded organelle in which molecules destined for secretion
are stored prior to release. Sometimes called secretory granule
because darkly staining contents make the organelle visible as
a small solid object.
SER:
see smooth endoplasmic reticulum
serine/threonine kinase:
Protein kinase that phosphorylates serines or threonines on its
target protein.
Sertoli cell:
Supporting cell of the mammalian testis that surrounds and nourishes
developing sperm cells.
sex chromosome:
Chromosome that may be present or absent, or present in a variable
number of copies, according to the sex of the individual; in mammals,
the X and Y chromosomes.
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