3.3 Cytoskeleton Flashcards
What is the cytoskeleton?
contains actin filaments, intermediate filaments, and microtubules, which maintains cell shape and allows its parts to move
How is the cytoskeleton structured?
the protein components interconnect and extend from the nucleus to the plasma membrane in eukaryotic
What is the cytoskeleton often compared to?
the bones and muscles of an animal
Why is the cytoskeleton dynamic?
because its protein components can assemble and disassemble as needed
What are actin filaments?
long, extremely thin, flexible fibres that occur in bundles or meshlike networks
What does each actin filament contain?
2 chains of globular actin monomers twisted about one another in a helical manner
What is the role of actin filaments?
they play a structural role when they form a dense, complex web just under the plasma membrane, to which they are anchored by special proteins
Where are actin filaments also seen?
in the microvilli that project from intestinal cells, and their presence accounts for the formation of pseudopods
What are pseudopods (false feet)?
extensions that allow certain cells to move in an amoeboid fashion
How do actin filaments produce movement?
they interact with motor molecules
What are motor molecules?
proteins that can attach, detach, and reattach farther along the actin filament
Give an example of a motor molecule.
myosin in muscle cells pull actin filaments along using the energy of ATP
myosin has both a head and a tail
the tails of several myosin molecules are joined to form a thick filament, while the heads interact with ATP and the actin filament
How are actin filaments involved in animal cell division?
the two new cells form when actin, in conjunction with myosin, pinches off the cells from one another
What are intermediate filaments?
roplelike assembly of fibrous polypeptides that vary according to the type of tissue
What’s the size of intermediate filaments?
intermediate in size between actin filaments and microtubules that will perform a structural role in the cell
What is the function of intermediate filaments?
- some support the nuclear envelope
- some support the plasma membrane
- some take par in the formation of cell-to-cell junctions
What do intermediate filaments do in skin cells?
intermediate filaments made of the protein keratin, provide mechanical strength
they are dynamic structures
What are microtubules?
small, hollow cylinders
have 13 rows of tubular dimers, surrounding what appears to be an empty central core
What are microtubules made up of?
the globular protein tubulin, which is of the 2 types, alpha and beta
What is the regulation of microtubule assembly controlled by?
a microtubule organizing centre
What is the centrosome?
the main microtubule organizing centre that lies near the nucleus in most eukaryotic cells
What do microtubules do?
they radiate from the centrosome, helping to maintain the shape of the cell and acting as tracks along which organelles can move
What motor molecule are associated with actin filaments?
myosin
What motor molecules are associated with microtubules?
kinesin and dynein
How are microtubules involved in cell division before it occurs?
they disassemble and then reassemble into a structure called a spindle
What is a spindle?
the spindle apparatus attaches to the chromosomes and ensures that they are distributed in an orderly manner
Are microtubules involved during cell division?
yes
How are microtubules involved after cell division?
the spindle disassembles and microtubules reassemble once again into their formal array
In animal cells, what do centrosomes contain?
2 centrioles lying at right angles to each other
What are centrioles involved in?
may be involved in the process of microtubule assembly and disassembly
What are centrioles?
short cylinders of microtubules with a 9+0 pattern of microtubule triplets (ring with 9 sets of microtubule triplets with none in the middle)
How are centrioles involved before animal cell division?
the centrioles replicate such that the members of each pair are again at right angles to one another
then, each pair becomes part of a separate centrosome
What happens to centrosomes after cell division?
centrosomes move apart and may function to organize the mitotic spindle
What are cilia and flagella?
hairlike projections that can move either in an undulating fashion, like a whip, or stiffy, like an oar
How do unicellular organisms called paramecia move?
by means of cilia
How do sperm cells move?
by means of flagella
What do cilia do in the human body?
the cells that line our upper respiratory tract have cilia that sweep debris trapped within mucus back up into the throat where it can be swallowed or ejected, this helps keep lungs clean
Describe cilia and flagella in eukaryotic cells.
- cilia are much shorter than flagella, but they have a similar construction
- both are membrane-bound cylinders
- cylinders are composed of 9 microtubule doublets arranged in a circle around 2 central microtubules
- 9+2 pattern of microtubules
- cilia and flagella move when the microtubule doublets slide past one another
What is the shaft of a flagellum or cillium?
the shaft of the flagellum has a ring of 9 microtubule doublets anchored to a central pair of microtubules
contains microtubule doublets whose side arms are motor molecules that cause the projection to move
