STPM Form 6 Biology Cytoskeleton


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STPM Form 6 Biology Cytoskeleton

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STPM Form 6 Biology Cytoskeleton

  1. 1. Cytoskeleton
  2. 2. Cytoskeleton Means “cell skeleton” Internal framework of cell Has many functions  Anchoring cell organelles  Provide cell shape  Aids in cell motility  Response to environmental signals Comprises  Microtubules  Microfilaments  Intermediate filaments
  3. 3. Made of proteins Dynamic properties Coordinate with each otherCoordinate with external signal
  4. 4. The cytoskeleton is composed ofnetworks of 3 different filaments
  5. 5. The cytoskeleton is dynamic
  6. 6. Microtubules Hollow tubes made of the protein tubulin  Alternating dimers of and tubulin Largest of cytoskeleton filaments Is used for:  Maintenance of cell shape  Motility  Flagella or cilia  Movement of organelles through cell  Often involves motor molecule  Often originate from centrosome  Spindle Fibres formation  Cell wall formation  Mechanical Support
  7. 7. Table 6-1a 10 µm Column of tubulin dimers 25 nm Tubulin dimer
  8. 8. Microtubules are organized toperform specific functions
  9. 9. Maintain Cell Shape
  10. 10. Holding Organelles in Place
  11. 11. Mechanical Support
  12. 12. Microtubule structure
  13. 13. The centrosome is the primarymicrotubule nucleation site inmost cells
  14. 14. Centrosome Microtubules Organizing Centre Hold centrioles
  15. 15. Location of Centrosome
  16. 16. Centrosomes act to polarize themicrotubule network Plus end - fast growing, usually in the cytoplasm Minus end - slow growing, anchored at the centrosome in most cells
  17. 17. Centrioles  Located in centrosome of animal cells  Occur in perpedicular pair  Have 9 triplets of microtubules  Facilitate microtubule assembly and chromosome separation in some cells  Divide during cell division
  18. 18. Fig. 6-22 Centrosome Microtubule Centrioles 0.25 µm Longitudinal section Microtubules Cross section of one centriole of the other centriole
  19. 19. Flagellum structure Basal body links flagellum or cilia to cell surface  Basal body looks just like a centriole 9 +2 arrangement of microtubules (eukaryotes) 9+0 arrangement of microtubules (prokaryotes) Radial spokes prevent dramatic sliding and only bending
  20. 20. Microtubule Organization ofFlagella
  21. 21. Movement of Cillia and Flagella
  22. 22. Fig. 6-24 Outer microtubule 0.1 µm Plasma doublet membrane Dynein proteins Central microtubule Radial spoke Protein cross- Microtubules linking outer doublets (b) Cross section of Plasma cilium membrane Basal body 0.5 µm (a) Longitudinal 0.1 µm section of cilium Triplet (c) Cross section of basal body
  23. 23. Basal Body
  24. 24. Structure  Microtubules  Alpha & Beta Tubulin  Microfilament  Actin molecules
  25. 25. Cell motility Cell movement facilitated by flagella or cilia Unlike in prokaryotes, eukaryotic flagella undulate Cilia are small appendages and they move like a swimmers arm-active stroke and return stroke
  26. 26. Fig. 6-25 Microtubule doublets ATP Dynein protein (a) Effect of unrestrained dynein movement ATP Cross-linking proteins inside outer doublets Anchorage in cell (b) Effect of cross-linking proteins 1 3 2 (c) Wavelike motion
  27. 27. Microfilaments Made of two intertwined strands of actin Helps maintain cell shape  Actin rearrangements allow engulfment events  Psuedopod formation in ameoba Promote cytoplasmic streaming in plants Essential for muscle contraction Used by invading bacteria to move around cell Frequently being assembled and disassembled within cell Cytokinesis
  28. 28. Table 6-1b 10 µm Actin subunit 7 nm
  29. 29. Microfilaments 2  Myosin interacts with actin to cause contraction  Cytoplasmic streaming and ameoboid motion are similar  Cortical cytoplasm around the perimiter of cell contains perpendicular actin (wind fence)  Streaming portion has parallel actin which facilitates cytoplasm movement  Plant cell wall prevents amoeboid movement of plant cell
  30. 30. Intermediate Filaments Resemble cable in structure Are made of protein subunits Help maintain cell shape Are durable and not assembled and disassembled as other cytoskeleton components May help maintain organelle position
  31. 31. Table 6-1c 5 µm Keratin proteins Fibrous subunit (keratins coiled together) 8–12 nm