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Cell Skeleton and Cell Movement - Q&A
1. What is a cytoskeleton? What are its main constituents in animal cells?
Cytoskeleton is the cytoplasmic structure that supports the cell, keeps its shape and fixates and moves the cell organelles. It is made of an extensive network of fibers dispersed in the cytoplasm and anchored in the plasma membrane. Its components are microtubules, microfilaments and intermediate filaments.
Cell Skeleton and Cell Movement - Image Diversity: the "cell skeleton"
2. Of which substance are microtubules made? In which structures and cellular processes do microtubules participate?
Microtubules are made of consecutive dimers of the protein tubulin (each dimer has an alpha and a beta tubulin associated). Microtubules participate in cell division, they are constituents of cilia and flagella and they also form the centrioles.
Cytoskeleton and Cell Movement - Image Diversity: microtubules tubulin
3. Of which substance are microfilaments made? What are the properties of these elements that give motility to cells?
Microfilaments are made of actin (a protein). The contractile association of actin with myosin and other cytoplasmic proteins give to microfilaments the ability to promote cell movement.
Cytoskeleton and Cell Movement - Image Diversity: microfilaments actin and myosin intermediate filaments
4. What are cell movements? How are these movements created?
Cell movements are movements performed by cell structures, like the movements of cilia and flagella, the pseudopod movements (in amoeba, macrophages, etc.), the cyclosis of the cytoplasm and the sarcomere contraction in muscle cells.
Cell movements can be created by the cytoskeleton action, by differences of viscosity among cytoplasmic regions and by intracellular contraction systems.
5. What are cilia and flagella? How do these structures acquire movement? What are some examples of ciliated and flagellated cells in humans?
Cilia and flagella are structures found in some prokaryotes as well in some eukaryotic cells. They play defense, nutrition and movement roles for the cell. In eukaryotic cells of protists and animals they originate from centrioles that migrate towards the plasma membrane and differentiate into structures projected outside the cell. Each cilium or flagellum is made of nine peripheral pairs of microtubules and one central pair all covered by membrane. (In bacteria, flagella are made of a protein named flagellin and there can also be fimbria made of pilin.)
In the fixation base of each cilium or flagellum in the plasma membrane there are proteins that work as molecular motors providing movement for these structures with energy spending. Due to this energy spending ciliated or flagellated eukaryotic cells have a large number of mitochondria.
In humans ciliated cells can be found, for example, in the bronchial and tracheal epithelium. In these tissues the cilia have the defensive function of sweeping mucous and foreign substances that enter the airways. Sperm cells are a typical example of flagellated cells, their flagellum is the propulsion equipment for the movement towards the ovule.
Cytoskeleton and Cell Movement - Image Diversity: ciliated cell flagellate cell
6. How does the amoeboid movement occur? What are examples of beings and cells that use such movements for locomotion?
Amoeboid movements are created by cytoplasmic movements and plasma membrane projections called pseudopods. Their formation actively changes the external shape of some portions of the cell surface making it move along a substratum. Pseudopods appear from differences of viscosity among neighboring regions of cytoplasm near the plasma membrane and from the contractile action of microfilaments.
Amoeboid movements occur, for example, in amoebas (a protozoan), organisms that use their movement to find food. The leukocytes, cells of the immune system, when attracted by chemical substances (immune mediators) use amoeboid movements to get out from capillaries in regions of tissue damage to participate in the inflammatory process.
Cytoskeleton and Cell Movement - Image Diversity: pseudopods
7. What are some examples of movement created by the contraction of sarcomeres of the muscle cells?
The handling of a cup of coffee, the peristaltic movements of the bowels, the cardiac beats and even a smile are examples of movement created by contraction of the sarcomeres of the muscle cells. This contraction is a type of cell movement.
8. What is cyclosis?
Cyclosis is a type of internal cell movement in which an oriented flow of circulating material is created and maintained in the cytoplasm by the action of microfilaments. Cyclosis is more easily observed in plant cells.
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