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mosaic:
In genetics, an organism made of a mixture of cells with different
genotypes.
motif:
Element of structure or pattern that recurs in many contexts;
specifically, a small structural domain that can be recognized
in a variety of proteins.
motor protein:
Protein that uses energy derived from nucleoside triphosphate
hydrolysis to propel itself along a filament or polymeric molecule.
MPF (M-phase-promoting factor):
Protein complex containing cyclin and a protein kinase that
triggers a cell to enter M phase. (Originally called maturation-promoting
factor.)
mRNA (messenger RNA):
RNA molecule that specifies the amino acid sequence of a protein.
Produced by RNA splicing (in eucaryotes) from a larger RNA molecule
made by RNA polymerase as a complementary copy of DNA. It is
translated into protein in a process catalyzed by ribosomes.
MTOC:
see microtubule-organizing center
mutation:
Heritable change in the nucleotide sequence of a chromosome.
myelin sheath:
Insulating layer of specialized cell membrane wrapped around
vertebrate axons. Produced by oligodendrocytes in the central
nervous system and by Schwann cells in the peripheral nervous
system.
myoblast:
Mononucleated, undifferentiated muscle precursor cell. A skeletal
muscle cell is formed by the fusion of multiple myoblasts.
myofibril:
Long, highly organized bundle of actin, myosin, and other proteins
in the cytoplasm of muscle cells that contracts by a sliding
filament mechanism.
myosin:
Type of motor protein that uses ATP to drive movements along
actin filaments. Myosin II is a very large protein that forms
the thick filaments of skeletal muscle that slide over actin
filaments during contraction. Myosin I is smaller, more widely
distributed, and not assembled into filaments; it is often membrane-bound.
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