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src gene:
Name of the first retroviral oncogene discovered (v-src)
and its precursor proto-oncogene (c-src). The product of
these genes is a membrane-associated protein kinase that phosphorylates
many target proteins on tyrosine residues. (From sarcoma,
the type of cancer that the src virus causes; pronounced ”sark.”)
starch:
Polysaccharide composed exclusively of glucose units, used as
an energy store in plant cells.
Start:
Important checkpoint in the eucaryotic cell cycle. Passage through
Start commits the cell to enter S phase.
stem cell:
Relatively undifferentiated cell that can continue dividing indefinitely,
throwing off daughter cells that can undergo terminal differentiation
into particular cell types.
stereocilium:
A large, rigid microvillus found in ”organ pipe” arrays
on the apical surface of hair cells in the ear. A stereocilium
contains a bundle of actin filaments, rather than microtubules,
and is thus not a true cilium.
steroid:
Hydrophobic molecule related to cholesterol. Many important hormones
such as estrogen and testosterone are steroids.
striated muscle:
Muscle composed of transversely striped (striated) myofibrils.
Skeletal and cardiac muscles of vertebrates are the best-known
examples.
stroma:
(1) The connective tissue in which a glandular or other epithelium
is embedded.
(2) The large interior space of a chloroplast, containing enzymes
that incorporate CO2 into sugars.
structural gene:
Region of DNA that codes for a protein or for an RNA molecule
that forms part of a structure or has an enzymatic function; as
distinct from regions of DNA that regulate gene expression.
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