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4.8 The Cytoskeleton
The structure and function of actin filaments are compared.
Cells are exposed to a lot of physical forces.
Cell shape, movement, and internal transport all require structural support.
Prior to the 1970s, it was thought that the cytoplasm was a mixture of organic molecules.
The cytoplasm was shown to be highly organized by high-voltage electron microscopes.
The makeup of the cytoskeletal network was identified by the technique of immunofluorescence microscopy.
The cell's shape is maintained by the cytoskeleton.
The cytoskeleton is made up of three types of components.
They can be seen using labeling and microscopy.
Cells have a twisted double chain of actin.
The animal cells have ropelike intermediate fibers.
A peacock's colorful feathers are strengthened.
The animal cells are hollow and made of tubulin dimers.
A chameleon's skin cells use microtubules to move their pigment around so that they can see the color of their environment.
The bones and muscles of an animal are compared to the cytoskeleton.
In response to changes in internal and external environments, the cytoskeleton can rearrange its components.
There are a number of different mechanisms that regulate this process.
There are two chains of actin monomers twisted around each other.
Actin filaments are anchored by special proteins and provide structural support as a dense, complex web.
When an amoeba moves over a surface with pseudopods, actin filaments can rearrange themselves and facilitate cellular movement.
In plant cells, actin filaments form the tracks along which chloroplasts move in a specific direction.
The actin filaments are pulled along this way by the motor molecule myosin.
Myosin has a head and a tail.
In muscle cells, the myosin molecule's tails are joined together.
Actin and myosin pinch off the cells from one another during animal cell division.
Intermediate filaments are named because they are intermediate in size between actin and microtubules.
They form a ropelike assembly of polypeptides, but the specific type varies according to the tissue.
The formation of cell-to-cell junctions is supported by some intermediate filaments and not by others.
The skin cells have great mechanical strength due to the intermediate filaments made of the keratin protein.
Intermediate filaments are similar to other components in that they are highly dynamic and disassemble when added to them.
"small" cylinders are 25 to 25 um in diameter and 0.2 to 25 um in length.
There are two types of tubulin, alpha and b.
When assembly occurs, a and b tubulin molecules come together as dimers, and the dimers arrange themselves in rows.
There are 13 rows of tubulin dimers surrounding what appears to be an empty central core.
The Page 76 microtubule-organizing center is in charge of the microtubule assembly.
The main MTOC is located in the centrosome.
The center is near the nucleus.
Microtubules help to maintain the shape of the cell and act as tracks that can be moved.
Different types of kinesin are used to move different types of cells.
The molecule dynein is found in flagella.
Page 77 reassembles into a structure called a spindle, which distributes chromosomes in an orderly manner, before a cell divides.
Plants have evolved different types of poisons that prevent them from being eaten.
colchicine is a plant poison that blocks the assembly of tubulin.
There are two centrioles lying at right angles to each other in animal cells.
The major microtubule-organizing center for the cell is a centrosome.
It is possible that centrioles are involved in the process of assembling and disassemble.
Before an animal cell divides, the centrioles replicate, and the members of each pair are at right angles to one another.
Each pair becomes a separate centrosome.
The centrosomes move apart during cell division, which is the most likely function.
Each new cell has its own centrosome and pair of centrioles.
The equivalent of a centrosome is found in plant and fungal cells, but they don't have centrioles.
Two centrioles are positioned at right angles to each other in the centrosome of an animal cell.
There is a micrograph of one centrosome.
What the centrosome does for the cell may be what a basal body does for a cilium or flagellum.
The centrioles are believed to give rise to the basal bodies.
"whip") are projections that can move either in an undulating fashion, like a whip, or stiffly, like an oar.
In free cells, flagella move the cell through liquid.
Single-celled paramecia are organisms that move by means of cilia, whereas sperm cells move by means of flagella.
The cells that line our upper respiratory tract have cilia that can sweep mucus back up into the throat, where it can be swallowed or expelled.
The action helps keep the lungs clean.
There is a similar construction to flagella in eukaryotic cells.
There are two cylinders enclosing a matrix area.
The matrix has nine pairs of microtubules arranged in a circle around two central microtubules, which is called the 9 + 2 pattern.
When the pairs of microtubules slide past one another, Cilia and flagella move.
The flagellum has a 9 + 0 pattern of microtubule triplets.
The flagellum's shaft has a 9 + 2 pattern, with a ring of nine pairs of microtubules around the central pair.
The flagellum's outer pairs have side arms of dynein, which is a motor molecule.
Thedynein side arms attempt to move along their neighbors in the presence of ATP.
Because of the spokes connecting the pairs, bending occurs.
Each cilium and flagellum has a body in the cytoplasm.
Basal bodies are believed to be derived from microtubule triplets.
It is possible that the microtubules are organized by the bodies, but this idea is not supported by the fact that cilia and flagella grow by the addition of tubulin dimers to their tips.
The components of the cell's skeleton are different.
The exchange of materials between the inside and outside of the cell is regulated by the plasma membrane.
The archaeans are included in the prokaryotes.
THelakoids are included in the cytoplasm of cyanobacteria.
The membranous are in constant communication.
The nucleus is copied from the DNA and then the nucleus is exited through a nuclear pore.
Most of the time this assembly goes to the rough ER to make a protein after a ribosome is attached to an mRNA.
The Golgi apparatus modifies, sorts, and repackages things.
Microbodies have specific functions.
Cells need constant input of energy.
Actin, intermediate, and microtubules are found in the cytoskeleton.
The shape of the cell is maintained by these.
They are used as an internal transport system.
Pick the best answer for the question.
The basic units of life are cells.
A spherical cell is called a coccus.
The _____ is responsible for the synthesis of the molecule in the cell.
Vesicles from the ER are on their way to the peroxisomes.
Vesicles have specific functions in a cell.
This type of microbody contains catalase to break down hydrogen peroxide.
The cells are involved in cellular respiration.
The same pattern of microtubules is found in flagella a.
Scientists have discovered that an antibiotic that is effective against the protist will kill the parasites.
The lysosome is not able to produce the enzymes necessary for normal functioning due to a faulty gene.
Suggest a cellular organelle that could be genetically modified to perform the same function as the lysosome.
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