|Lecture Notes:: 10 October
© R. Paselk 2001
Practice Exam First Hour
The Cell, cont.
The Eukaryote Cytoskeleton
Eukaryotic cells also have a cytoskeleton of protein fibers
providing support , organization, and enabling mobility within
and by the cell. There are three major types of cytoskeletal elements
(Table7.2, p 119):
- Microtubules (Figures 7.21-25. pp 121-3): 25 nm diameter
hollw tubes made up of the protein tubulin (a,b-dimers)
arranged in 13 columns of protein monomers. Used for:
- Maintaining cell shape as compressive elements.
- As "tracks" for the rapid movement of cell organells
via cell "motors" (Dyneins) [overhead].
- They make up the mitotic apparatus for cell division, providing
the basis of chromosome movement (involves treadmilling?).
- They make up the centrioles, which seem to function in organizing
the microtubules of the mitotic apparatus in animal cell division.
- The make up the skeleton and are the base of sliding motility
in cilia and flagella [overhead]
- Actin Filaments (microfilaments) (Figures 7.26-7,
pp 123-4): 7 nm diameter helical double strands made up
of two intertwined filaments of actin monomers. Used for:
- Maintaining cell shape as tension elements.
- "Treadmilling" used in some aspects of changing
- Interaction with myosins enable various types of cell motility:
- ameboid movement - extension and contraction of pseudopodia.
- cytoplasmic streaming - circular movement of cytosol and
cell contents to distribute materials within cells.
- Cleavage furrow formation in cell division.
- As tension elements and "tracks" in muscle contraction
- Intermediate Filaments (Figures 7.20, .26, pp 119
& 123): 8-12 nm diameter bundles of supercoiled fibrous proteins
(keratins). Used for:
- Maintaining cell shape as tension elements - more permanent
than either microtubules or microfilaments tend to be.
- Anchor the nucleus and other cell organelles.
- Last modified 15 October 2001
- © R Paselk