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Cell Structure, Motility and Junctions

Cell Structure, Motility and Junctions. Chapter 6. Microscopes. Size limitations. Organelles . See chart Part to Whole and What Kind of Cell Lysosome. Organelles. Interactions of endomembrane. Organelles . Mitochondria and Chloroplasts. Cytoskeleton.

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Cell Structure, Motility and Junctions

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  1. Cell Structure, Motility and Junctions Chapter 6

  2. Microscopes

  3. Size limitations

  4. Organelles • See chart Part to Whole and What Kind of Cell • Lysosome

  5. Organelles • Interactions of endomembrane

  6. Organelles • Mitochondria and Chloroplasts

  7. Cytoskeleton • A network of protein filaments that extends throughout the cytoplasm • Functions: • Support and reinforce the cell and maintains shape • Organize the cell by anchoring the organelles in place • Movement (motility) of the cell by moving part or whole using motor proteins (break down skeleton in one part and rebuild in another part = new shape of cell) • Composed of 3 types of molecular structures • Microtubules • Microfilaments • Intermediate filaments

  8. Microtubules • Structure: Straight, hollow cylinder • Size: Largest cytoskeletal part • Protein: tubulin (globular) • Functions: • Spindle fibers to move chromosomes (from centrosomes) • Can disassemble and rebuild quickly • Cell shape • Move organelles using motor proteins • Make up the structure of cilia and flagella which are used for cell locomotion or for moving substances across the cell surface (windpipe, fallopian tubes)

  9. Microfilaments • Structure: Thin, solid part of the cytoskeleton • Size: smallest • Protein:Made of actin (2 helically twisted polypeptide chains) • Functions: • Maintains cell shape or changes cell shape • Anchors membrane proteins • Work in muscular contractions (actin and myosin filaments) by sliding past one another • Help with cytoplasmic streaming to circulate nutrients • Pseudopodia • Cleavage furrow formation in cell division

  10. Microfilaments and Motility • Muscular contractions • Amoeboid movement • Cytoplasmic streaming

  11. Intermediate Filaments • Structure: Made of fibrous proteins supercoiled into thick cables; More permanent part of cytoskeleton • Size: between microtubules and microfilaments • Protein: keratin family • Function: • Helps to maintain cell shape and shape of cell parts • Helps to anchor organelles and nucleus • Often dissembled and reassembled

  12. Motility • Cells move vesicles, chromosomes and others using microtubules and microfilaments • Motor proteins provide energy from ATP hydrolysis to make cells and vesicles move along “monorails” • Motor proteins in microtubules: kinesins and dyneins • Motor proteins in microfilaments: myosins

  13. Cell Junctions • Places in adjoining cell membranes where a cell sends and receives signals and materials and where it recognizes and attaches itself to similar cells • Types: • Tight Junctions • Adhering/Anchoring Junctions (Desmosomes) • Gap Junctions (animals) OR plasmodesmata (plants)

  14. Tight Junctions • Plasma membranes of neighboring cells are tightly pressed together; bound by proteins • Link cells of most body tissues (skin, internal cavities, organs) • Prevent leakage • Ex – skin cells (watertight) • Ex – stomach cells (keep acid in)

  15. Anchoring/Adhering Junctions (Desmosomes) • Fasten cells together in strong sheets • Join cells in skin, heart, organs • Can stretch • Ex – bladder • Ex – muscles (“muscle tears” = breakage of these junctions)

  16. Gap/Communicating Junctions • Link cytoplasm of neighboring cells for open channel of signals and substances (sugar, ions, AAs) through a pore • Helps in cell communication • Ex – heart cells beat as one • Ex – embryonic development • Ex – plasmodesmata in plants move water and small solutes

  17. Cell Communication • One cell signals another to change its activities • Coordinates activities of multicellular organisms *More on this later in Ch 11*

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