Download Chapter 17. Cytoskeleton Chapter 17. Cytoskeleton Chapter 17

Chapter 17. Cytoskeleton
• Cells are not “bags of enzymes”, but rather
organized in three dimensions.
• This organization is carried out by the
cytoskeleton, the “bones and muscles” (and
more) of cells.
• Cells are thousands of times larger than a
typical molecule. Therefore the cytoskeleton
must logically be made by stringing together
multiple smaller subunits.
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Chapter 17. Cytoskeleton
• Two things to keep an eye on:
– The role of polymerization (and in some cases
depolymerization)
– The manner in which the cytoskeletal molecules
interact with the rest of the cell. Often this is
due to accessory proteins.
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Chapter 17. Cytoskeleton
• An overview of the three major
components of the cytoskeleton.
Intermediate filaments
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Fig. 17.2
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Chapter 17. Cytoskeleton
• An overview of the three
major components of the
cytoskeleton.
– Microtubules
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Fig. 17.2
Chapter 17. Cytoskeleton
• An overview of the three
major components of the
cytoskeleton. (Fig 17-2)
– Actin Filaments
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Fig. 17.2
Chapt 17. Intermediate Filaments
• Intermediate filaments are mostly involved
with strengthening organelles and cells.
• Intermediate filaments are stable.
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Chapt 17. Intermediate Filaments
• The construction of intermediate filaments.
(Fig 17-4)
– The monomer consists of conserved and variable
regions.
– There are multiple kinds of monomers.
– Different kinds of monomers differ primarily in
the NH2 and COOH ends
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Fig. 17.4
Chapt 17. Intermediate Filaments
• The construction of intermediate filaments.
(Fig 17-4)
– Dimerization retains polarity, but the tetramer
is antiparallel (and thus both ends are
equivalent).
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Fig. 17.4
Chapt 17. Intermediate Filaments
• The construction of intermediate filaments.
(Fig 17-4)
– Packing into a filament.
– The overlap between
subunits contributes
to the
strength of
the filament.
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Fig. 17.4
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Chapt 17. Intermediate Filaments
• There are multiple kinds of chemically
distinct intermediate filaments.
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Fig. 17.6
Chapt 17. Intermediate Filaments
• There are multiple kinds of chemically
distinct intermediate filaments.
– The keratins.
Desmosomes
Intermediate Filaments
Hemidesmosomes
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Fig. 17.5
Basement membrane
Chapt 17. Intermediate Filaments
• Evidence that the keratins really function as
structural supports for epithelial cells:
Epidermolysis bullosa simplex.
Fig. 17.5
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The
cytoskeleton
rearranges
depending on
the cell-cell
junctions
that are
present in
the cell.
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Chapt 17. Intermediate Filaments
• There are multiple kinds of chemically
distinct intermediate filaments. (Fig 17-6)
– Vimentin and related IF’s.
• An example: certain Ifs hold muscle sarcomeres in
place.
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Chapt 17. Intermediate Filaments
• There are multiple kinds of chemically
distinct intermediate filaments.
– Neurofilaments.
Cell Body
Axon
AxonTerminus
Dendrite
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Chapt 17. Intermediate Filaments
– The IF typically make much less use of accessory
proteins than do the other 2 classes (MT and
actin).
– However, the accessory protein plectin cross
links many IF to other cytoskeletal polymers and
organelles.
• Abnormal plectin results in symptoms of
– Epidermolysis bullosa simplex
– Muscular dystrophy
– Neurodegeneration.
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Chapt 17. Intermediate Filaments
• There are multiple kinds of chemically
distinct intermediate filaments.
– Lamins.
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Fig. 17.8
Chapt 17. Intermediate Filaments
• Lamins:
– Responsible for the integrity of the nuclear
envelope.
– Differ from most intermediate filaments in that
they form a meshwork rather than a simple
linear filament.
– Also differ from other IFs because they can
disassemble and reassemble.
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Chapt 17. Intermediate Filaments
• Summary: IFs ……..
– Are primarily structural.
– Have long lifetimes -- in most cases an IF is an
IF forever.
– Carry out different functions in different cells
by being chemically distinct.
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