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Transcript
Cytoskeleton
Cristina Botello-Godoy, Karina Garcia,
Takara Reed, Aida Rogonich
Eukaryotic vs. Prokaryotic
Cytoskeleton
• Animals, fungi,
protozoans, algae, etc.
• Much larger & more
complex, as are the cells
• Structure’s include: shape
& strong cell wall, allow
for cell movement (within
cells & endocytosis), cell
division
• Bacteria
• Smaller & less complex,
as are the cells
• Structure’s include: shape
& strong cell wall, cell
division
Prokaryotic Cytoskeleton
• Recent study has found that bacteria cells
too consist of a cytoskeleton
• Research is based on the fact that the
proteins of prokaryotic & eukaryotic cells
are homologues
• Evolution is diverse between the two cell
types, so more concepts allowed for this
approach
Prokaryotic Cytoskeleton
• Network of structural filaments
• 3-D structure
• Maintains cell shape, structure, protection,
polarity, and cell division
• Some structures are still UNIDENTIFIED
• Proteins similar to those of eukaryotic cells
discovered
Protein Functions
FtsZ:
• tubulin-like
• forms filaments, but
they do not group into
tubules
• maintains
organization
• required for cell
division
MreB:
• actin-like
• determines cell shape
• positions polar
proteins
• forms a network (helix
shaped) under the
cytoplasmic
membrane, that
directs proteins
Protein Functions
CreS:
• crescentin
• intermediate filament like
• maintains cell shape and
form of bacteria
• filament connects from
pole to pole
ParM:
• actin-like
• allow for cell division
• acts like kinetochore
complez
• separation of plasmids by
the filaments is
analogous to
microtubules allowing cell
division during eukaryotic
mitosis
Cytoskeleton
Cytoskeleton Function
• The Cytoskeleton has many important functions. One of
its most important functions is to provide structure for the
cell, it makes sense if you break up the word cytoskeleton.
• -The cytoskeleton also acts as a scaffolding, with this the
organelles in the cell are able to stay attached.
• -The cytoskeleton is also used for the movement of the
cell. The internal movement of cell organelles, as well as
cell locomotion and muscle fiber contraction could not
take place if it wasn’t for the cytoskeleton.
• -The cytoskeleton is also required for the division of cells
during mitosis or meiosis.
Endoplasmic Reticulum (E.R.)
• The Endoplasmic Reticulum is the factory in the cell that produces
proteins and lipids of most of the cells’ s organelles.
• The E.R is mainly responsible for transporting proteins and other
carbohydrates to wherever they are needed in the cell.
• The E.R is composed of many folds, say you fold a piece of gum
over and over that’s how the E.R looks.
• There are two types of E.R, a Rough E.R and a Smooth E.R
• The Rough E.R is rough because it has ribosome attached to it. In
the Rough E.R proteins are made .
• The Smooth E.R doesn’t have any thing attached to it, that’s why its
called smooth
• The Smooth E.R is the one that releases the proteins produced in
the Rough E.R
Cell Shape
• The cell shape depends on what type of
cell it is
• If the cell is an animal cell than most likely
the cell is circular because it doesn’t
contain a cell wall
• If the cell is rectangular or like a square
then the cell is an animal cell, the cell
takes the shape of the cell wall
Cytoskeleton Structure
• Imagine walking into George’s basement.
All you see is a bunch of glow in the dark
cables hanging over your head. These
cables surround the machines that operate
our school. These cables are the
cytoskeleton, which surrounds the cells
that help function our body. =)
Cytoskeleton Structure
• The Cytoskeleton is a complex threedimensional structure that is found in
the cytoplasm of the cell. It’s composed
of fibers primary microtubules being the
thickest of three, microfilaments, the
thinnest, and intermediate filaments in
the middle range.
Microtubules
• Microtubules are one of the
components of the
cytoskeleton.
• They are rigid hollow rods that
have a diameter of 25
nanometers and length of
anywhere between 200
nanometers and 25
micrometers.
• Microtubules serve as
structural components within
cells and are involved in many
cellular processes including
mitosis, cytokinesis, and
vesicular transport.
Centrosomes, Centrioles, Cilia &
Flagella
• Centrosomes organize the
microtubules.
• They also regulate cell-cycle
progression.
• This occurs in the cytoplasm
attached to the outside of the
nucleus.
• In nine triplet sets (star
shaped), microtubules form
Centrioles surrounded by a
solid mass of protein called the
“pericentriolar material.”
• In nine doublets oriented
about additional microtubules
(wheel-shaped) microtubules
form cilia & flagella.
Centrosomes & Centrioles
Centrosomes & Centrioles
ANIMAL CELLS:
•
•
The centrosome, also called the •
"microtubule organizing center“
(MTOC), is a region in the cell
where microtubles are formed.
•
Within an animal cell centrosome,
there is a pair of small organelles
known as the centrioles which
each make up of a ring of nine
groups of microtubules. (see
•
picture).
The two centrioles are arranged
so that one is perpendicular to the
other.
During animal cell division, the
centrosome divides and the
centrioles replicate which results
in two centrosomes that each
have its own pair of centrioles.
The two centrosomes move to
opposite ends of the nucleus, and
from each centrosome,
microtubules grow into a "spindle"
which is responsible for separating
replicated chromosomes into the
two daughter cells (Mitosis
process).
Centrosomes & Centrioles
• PLANT CELLS:
• Plant cells have centrosomes that function
much like animal cell centrosomes.
However, unlike centrosomes in animal
cells, they do not have centrioles.
Cilia & Flagella
•
Both cilia and flagella are created from
microtubules, and both supply:
–
–
•
Both have the same basic structure.
–
–
•
•
•
•
“Locomotion” for the cells (like sperm)
And the movement of fluid past the
cells
If the microtubules are short, they are
cilia
Or only one or a few long ones, they
are flagella.
Each cilium or flagellum is made of:
a cylindrical collection of 9 evenlyspaced microtubules, each with an
incomplete microtubule attached to it.
This gives the structure a "figure 8"
appearance when view in cross
section. (see bottom picture).
2 single microtubules run up through
the center of the bundle, completing
the so-called "9+2" pattern.
The entire assembly is enclosed in a
membrane that is basically an
expansion of the plasma membrane.
Microfilaments (actins filaments)
• Solid rods about 7 nm
in diameter
• made from actin a
globular protein, in
the form of a double
twisted chain
• Structural role is to
bear tension, resist
the pulling forces
within the cell
Actin subunit
7 nm
Microfilaments (actins filaments)
• Forms a 3-D network
called the cortex just
inside the plasma
membrane to help
support the cell’s
shape
• make up the core of
microvilli of intestinal
cells
Microfilaments (actins filaments)
• Microfilaments are known to assist in cell
motility.
– In muscles cells thousands of actin filaments
are arranged parallel to one another along the
length of a muscle cell, interlinking with
thicker filaments made of the protein myosin.
Myosin acts as a motor protein as projections
walk along the actin filaments.
Muscle cell
Actin filament
Myosin filament
Myosin arm
(a) Myosin motors in muscle cell contraction
Microfilaments (actins filaments)
Cortex (outer cytoplasm):
gel with actin network
Extending
pseudopodium
Inner cytoplasm: sol with
actin subunits
– Amoeboid movement
interaction of actin
filaments with myosin
near the cell’s trailing
end squeezes the
interior fluid forward
into the pseudopodium
Microfilaments (actins filaments)
• Main functions:
– Maintenance of cell shape (tension-bearing
elements)
– Changes in the cell shape
– Muscle contraction
– Cell motility
• Myosin
• Pseudopodia
– Cytoplasmic streaming
Intermediate Filaments
Keratin proteins
Fibrous subunit (keratins
coiled together)
• Diameter of 8-12nm,
• As well as
Microfilaments, it is
specialized for
bearing tensions.
• Constructed of
different molecular
subunits belonging to
a family of proteins
whose members
include the keratin
Intermediate Filaments
• Are more permanent fixtures of cells then microtubules and
microfilaments
– After cells die intermediate filaments are still found on the cells
• Experiments suggest that intermediate filaments are of greater
importance in reinforcing the shape of a cell and organelles .
– Nucleolus is surrounded by intermediate filaments that hold it in place
within the cell
– Also makes up the nuclear lamina inside the nuclear envelope
Resources
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Internet:
http://student.ccbcmd.edu/courses/bio141/lecguide/unit3/eustruct/cytosk.ht
ml
http://en.wikipedia.org/wiki/Cytoskeleton
http://en.wikipedia.org/wiki/Prokaryotic_cytoskeleton
www.bio.miami.edu
www.cancerquest.org
www.darwin.nmsu.edu
http://www.cellsalive.com/cell/centriol.htm
http://users.rcn.com/jkrmball.ma.ultranet/BiologyPages/c/Cytoskeleton.htm
http://www.ncbI.nlm.nih.gov/books/bv.fcgi?indexed+google&rid+cooper.secti
on1820
Books:
AP Biology (7th Edition) by Campbell Reece