Microtubles

1. http://literacy.purduecal.edu/student/djgibson/sunriseuniversity/sr-buttons-and-quicktips2http://literacy.purduecal.edu/student/djgibson/sunriseuniversity/sr-buttons-and-quicktips2 Introduction Introduction Cytoskeleton Begin Quiz Microtubles Microtubles Microfilaments Microfilaments Internal Screen Tip – Tutorial Banner Cell Movement Cell Movement External You should learn that the cytoskeleton is both a muscle and a skeleton, and is responsible for cell movement, cytokinesis, and the organization of the organelles within the cell. Intermediate Filaments Intermediate Filaments Quiz Quiz Back Cytoskeleton Tutorial http://www.biology.arizona.edu/cell_bio/tutorials/cytoskeleton/main.html

3. Introduction You should learn that the cytoskeleton is both a muscle and a skeleton, and is responsible for cell movement, cytokinesis, and the organization of the organelles within the cell.

4. Cytoskeleton The cytoskeleton is unique to eukaryotic cells. It is a dynamic three-dimensional structure that fills the cytoplasm. This structure acts as both muscle and skeleton, for movement and stability. The long fibers of the cytoskeleton are polymers of subunits. The primary types of fibers comprising the cytoskeleton are microfilaments, microtubules, and intermediate filaments.

5. Microfilaments Microfilaments are fine, thread-like protein fibers, 3-6 nm in diameter. They are composed predominantly of a contractile protein called actin, which is the most abundant cellular protein. Microfilaments' association with the protein myosin is responsible for muscle contraction. Microfilaments can also carry out cellular movements including gliding, contraction, and cytokinesis.

6. Microtubules Microtubules also form the spindle fibers for separating chromosomes during mitosis. When arranged in geometric patterns inside flagella and cilia, they are used for locomotion. This structure acts as both muscle and skeleton, for movement and stability. The long fibers of the cytoskeleton are polymers of subunits. The primary types of fibers comprising the cytoskeleton are microfilaments, microtubules, and intermediate filaments.

7. Intermediate Filaments Intermediate filaments are about 10 nm diameter and provide tensile strength for the cell.

8. Examples of the cytoskeleton in epithelial cells In the epithelial (skin) cells of the intestine, all three types of fibers are present.

11. External cell movement Cellular movement is accomplished by cilia and flagella. Cilia are hair-like structures that can beat in synchrony causing the movement of unicellular paramecium. Cilia are also found in specialize linings in eukaryotes. For example, cilia sweep fluids past stationary cells in the lining of trachea and tubes of female oviduct. Flagella are whip-like appendages that undulate to move cells. They are longer than cilia, but have similar internal structures made of microtubules. Prokaryotic and eukaryotic flagella differ greatly. Cellular movement is accomplished by cilia and flagella. Cilia are hair-like structures that can beat in synchrony causing the movement of unicellular paramecium. Cilia are also found in specialize linings in eukaryotes. For example, cilia sweep fluids past stationary cells in the lining of trachea and tubes of female oviduct. Flagella are whip-like appendages that undulate to move cells. They are longer than cilia, but have similar internal structures made of microtubules. Prokaryotic and eukaryotic flagella differ greatly. Flagella & cilia have a 9 + 2 arrangement of microtubules. This arrangement refers to 9 fused pairs of microtubules on the outside of a cylinder, & 2 unfused microtubules in the center. Dynein "arms" attached to microtubules serve as molecular motors. Defective dynein arms cause male infertility and lead to respiratory tract and sinus problems. Flagella & cilia have a 9 + 2 arrangement of microtubules. This arrangement refers to 9 fused pairs of microtubules on the outside of a cylinder, & 2 unfused microtubules in the center. Dynein "arms" attached to microtubules serve as molecular motors. Defective dynein arms cause male infertility and lead to respiratory tract and sinus problems.

12. SpermBelow are two cross-sections of sperm tails (flagella).

13. Internal cell movement The cytoskeleton acts as a "track" on which cells can move organelles, chromosomes and other things. Some examples are: Vesicle movement between organelles and the cell surface, frequently studied in the squid axon.

14. Internal Cell Movement Examples

15. Cellular Motors Cells have protein motors that bind two molecules, and using ATP as energy, cause one molecule to shift in relationship to the other. Two types of these protein motors are myosin and actin, and dynein or kinesin and microtubules. These families of proteins all have a motor end, but may have several kinds of different molecular structures on the binding end. When these proteins bind, they can cause many different molecules, organelles, etc. to move.

16. Broken Motors In healthy individuals, the protein dystrophin is part of the linkage between the cellular cytoskeleton and the adhesive proteins on the outside of the cell. In Duchenne Muscular Dystrophy, however, the gene that codes for dystrophin is defective, resulting in muscle degeneration and finally death. This disease is X-linked recessive and occurs in 1 out of every 3,500 males.

17. To the right is an example of the different binding ends found in the kinesin family of motors. When linked to other microtubules, protein motors can cause motion if the ends are fixed or extend the lengths of the fiber bundles if the ends are free. INTERNAL, Cellular Motors

18. Immotile cilia syndrome patients have defective ________. Cytochalasins Drugs that interfere with actin polymerization into microfilaments. Microtubules The group of related genes are called a _________. Dynein What Dynein mechanism is responsible for movements of cilia and flagella? Family

19. Problem 1: Immotile Cilia Syndrome Immotile cilia syndrome patients have defective _______. • myosin • tubulin • dynein • actin C.cCorrect.Dynein is the molecular motor responsible for the movement of microtubules in cilia and flagella. The defect in immotile cilia syndrome is caused by alterations in dynein. Drag and Drop Quiz - Cytoskeleton

20. Problem 2: Single Kind of Motor Explain how a single kind of "motor" can cause movement of a wide variety of substances, including vesicles, chromosomes, proteins, etc. A. Nature has evolved many different mechanisms or motor proteins, each unrelated to the other and with independent mechanisms/including vesicles, chromosomes, proteins, etc. B. Multi-gene families of motor proteins have the mechanism for moving along microtubules in common and have the other part of the same protein altered to allow binding to a variety of substances. B. Multi-gene families of motor proteins have the mechanism for moving along microtubules in common and have the other part of the same protein altered to allow binding to a variety of substances. Correct.Nature invents a trick, i.e. movement along microtubules, and then uses the mechanism in many different ways. The group of related genes are called a family.

21. Problem 3: Cilia and Flagella • What mechanism is responsible for movements of cilia and flagella? A.Kinesin moving on microfilaments B. Dynein moving on microfilaments C. Dynein moving on microtubules D. Myosin moving on microfilaments C. Dynein moving on microtubules Correct.Dynein is the correct motor for microtubules functional as cilia and flagella.

22. Problem 4: Cytochalasins • Cytochalasins are drugs that interfere with actin polymerization into microfilaments. If you add cytochalasin to cultured mammalian cells that have just begun mitosis what is most likely to happen? A. The cells will arrest at mitotic metaphase. B. The cells will cease metabolism and die. C. The cells will complete mitosis and arrest at cytokinesis. D. The cells will arrest at mitotic anaphase. C. The cells will complete mitosis and arrest at cytokinesis. Correct.Microfilaments are needed for cytokinesis.

23. Problem 5: Chromosome Movement • Which of the following experimental observations would suggest that chromosomes move by polymerization of tubulin subunits? • A. Energy is expended in the process of chromosome movement. • B. Chemicals that block tubulin subunit interactions also block chromosome movement. • C. Chromosomes move by sliding past one another. • D. Chromosomes are individually attached to microtubules. B. Chemicals that block tubulin subunit interactions also block chromosome movement. Correct.Colchicine blocks tubulin subunit interaction, and blocks mitosis.

24. The following content was adapted from the University of Arizona’s Department of Biochemistry and Molecular (2004) “The Biology Project”