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Actin Filaments: 968 PANEL 16-1: The Three Major Types of Protein Filaments That Form The Cytoskeleton

The document summarizes the three major types of protein filaments that make up the cytoskeleton: 1) Actin filaments are flexible polymers of actin proteins that appear as networks and gels throughout the cell, but are most concentrated just under the plasma membrane. 2) Microtubules are rigid, hollow cylinders of tubulin proteins that are long and straight with one end attached to a centrosome. 3) Intermediate filaments are rope-like fibers made of various intermediate filament proteins that form meshworks like the nuclear lamina and span the cytoplasm, strengthening cells and tissues.

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342 views1 page

Actin Filaments: 968 PANEL 16-1: The Three Major Types of Protein Filaments That Form The Cytoskeleton

The document summarizes the three major types of protein filaments that make up the cytoskeleton: 1) Actin filaments are flexible polymers of actin proteins that appear as networks and gels throughout the cell, but are most concentrated just under the plasma membrane. 2) Microtubules are rigid, hollow cylinders of tubulin proteins that are long and straight with one end attached to a centrosome. 3) Intermediate filaments are rope-like fibers made of various intermediate filament proteins that form meshworks like the nuclear lamina and span the cytoplasm, strengthening cells and tissues.

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John
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968

PANEL 161: The Three Major Types of Protein Filaments That Form the Cytoskeleton

ACTIN FILAMENTS

ii

iii

100 nm

iv

25 nm
Actin filaments (also known as microfilaments) are two-stranded helical
polymers of the protein actin. They appear as flexible structures, with a
diameter of 59 nm, and they are organized into a variety of linear bundles,
two-dimensional networks, and three-dimensional gels. Although actin
filaments are dispersed throughout the cell, they are most highly
concentrated in the cortex, just beneath the plasma membrane.
Micrographs courtesy of Roger Craig (i and iv); P.T. Matsudaira and D.R. Burgess (ii); Keith Burridge (iii).

MICROTUBULES

ii

100 nm
iii

iv

25 nm
Microtubules are long, hollow cylinders made of the protein tubulin.
With an outer diameter of 25 nm, they are much more rigid than actin
filaments. Microtubules are long and straight and typically have one
end attached to a single microtubule-organizing center (MTOC)
called a centrosome.
Micrographs courtesy of Richard Wade (i); D.T. Woodrow and R.W. Linck (ii); David Shima (iii); A. Desai (iv).

INTERMEDIATE FILAMENTS

ii

iii

100 nm

iv

25 nm
Intermediate filaments are ropelike fibers with a diameter of around
10 nm; they are made of intermediate filament proteins, which constitute a
large and heterogeneous family. One type of intermediate filament forms a
meshwork called the nuclear lamina just beneath the inner nuclear
membrane. Other types extend across the cytoplasm, giving cells mechanical
strength. In an epithelial tissue, they span the cytoplasm from one cell-cell
junction to another, thereby strengthening the entire epithelium.
Micrographs courtesy of Roy Quinlan (i); Nancy L. Kedersha (ii); Mary Osborn (iii); Ueli Aebi (iv).

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