The Cytoskeleton

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The Cytoskeleton

• Protein filaments in the cytoplasm of eukaryotic
  cells that
• provide structural support for cell shape
• generate force for the movement of
  chromosomes, organelles, and whole cells

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Coomassie blue stain of fixed epithelial cell
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Electron Micrograph of a Detergent-Extracted
Platelet
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Microfilaments are double stranded polymers of
actin
Microtubes are hollow cylinders of the protein
tubulin
Intermediate filaments are very heterogeneous
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Keratin intermediate filaments and desmosomes
form cell sheets
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Electron micrographs of two types of intermediate
filaments in cells of the nervous system. (A)
neurofilaments in a nerve cell axon, showing the
extensive protein cross-bridges to provide great
tensile strength in this long cell process. (B)
glial filaments without cross-bridges. (C)
cross-section of an axon showing the regular
side-to-side spacing of the neurofilaments, which
greatly outnumber microtubules.
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Recessive Epidermolysis bulosa
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The nuclear lamina is made of lamin
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Indirect immunofluorescence
A bovine pulmonary artery endothelial cell
labeled with antibovine tubulin mouse monoclonal
antibody in combination with goat antimouse IgG
antibody) to stain microtubules.
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The CENTROSOME is an MTOC (microtubule organizing
center)
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axoneme
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Build A Microtubule
http//nessie.bch.ed.ac.uk/PAUL/MT/
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The Forth Railway Bridge across the Firth of
Forth in Scotland.
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Dynamic instability of microtubules
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http//www.bio.davidson.edu/misc/movies/tread3.MOV
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Selective stabilization of dynamic microtubules
by capping proteins can polarize a cell
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• Motor molecule families
• the dyneins move along microtubules
• the kinesins move along microtubules
• the myosins move along microfilaments

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kinesin moves toward plus end dynein moves
toward minus end
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cytoplasmic dynein and kinesin
http//www.kcl.ac.uk/depsta/biomedical/randall/ima
ges/squid.mov
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kinesin dynein
Membrane vesicle attached to MT
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Organelle placement
ER
Golgi
PLUS
MINUS
MT
MT
http//www.bio.unc.edu/faculty/salmon/lab/cler2b.m
ov
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Microtubules control chromosomal movement during
mitosis
http//www.bio.umass.edu/biology/wadsworth/movies/
prometaphase/reeling1.html
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This Sprite is named Twink
CILIA AND FLAGELLA
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Ciliated epithelium of human trachea
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Flagellum on sperm Flagella on Chlamydomonas
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Demonstration of microtubule sliding in a beating
sperm flagellum http//www.cco.caltech.edu/broka
wc/Demo1/BeadExpt.html
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Dynein deficiencies in humans lead to chroninc
bronchitis and sterility
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F-actin filaments from 3T3 cells stained with
phalloidin
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Cytochalasin produces binucleate cells
EM lab
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Monomeric G (globular) actin
G to F polymerization Blocked by cytochalasin
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G-actin (globular) F-actin (filamentous)
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Integrin clutch initiates forward movement
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Actin filament bundles terminate at contact
points with the glass slide on which cells are
crawling
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Muscle thin filaments
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