10 11 105 fa13 cell cell interactions skel

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  • Only some of the cells in a plant that can make them, have secondary cell wallsXylem plants have secondary cell walls
  • 10 11 105 fa13 cell cell interactions skel

    1. 1. Cell-Cell Interactions Dr. Corl BIOL 105 September 13, 2013
    2. 2. Cell-Cell Interactions • The cell surface • The extracellular layer • Cell-cell connections – Cell-cell attachments – Cell-cell gaps • Cell-cell communication (long distance)
    3. 3. The Cell Surface • Recall the structure of the plasma (cell) membrane: – Phospholipid bilayer w/ cholesterol molecules interspersed – Both integral proteins and peripheral proteins • Many of which have carbohydrate groups covalently attached!
    4. 4. The Extracellular Layer • Most organisms have an extracellular layer just exterior to the plasma membrane: – Provides an extra layer of protection / defense. – Helps define cell shape. – Helps attach one cell to a neighboring cell. • Broad types of extracellular layers: – Cell wall: • Surrounds plant, fungi, bacteria, and algal cells. – Extracellular matrix: • Surrounds animal cells.
    5. 5. The Extracellular Layer • Usually “fiber composites”: – Cross-linked network of long filaments (fibers) surrounded by a stiff ground substance. – Protects cell from stretching (tension) and compression.
    6. 6. The Plant Primary Cell Wall • Fibrous components = Cellulose microfibrils. • Ground substance = Pectins and other gelatinous polysaccharides.
    7. 7. The Plant Cell Wall • Primary cell wall: – Defines shape of plant cell. – Counteracts force of water entering the plant cell via osmosis: cell wall exerts wall pressure. • Secondary cell wall: – Secreted by certain plant cells. (e.g. xylem cells, above) – Secreted interior to the primary cell wall. – Can provide tough structural support (contains lignin).
    8. 8. The Plant Cell Wall • Secondary cell wall: – Contains the durable polymer lignin. – Found primarily in the xylem (water conducting) tissue of plants with a true vascular system: • e.g. Ferns, “evergreen plants,” and flowering plants. – Adaptation that allows vascular plants to grow tall and resist the force of gravity: • Xylem system acts like an internal skeleton!
    9. 9. The Extracellular Matrix (ECM) • Fiber composite secreted by animal cells. • Fibrous component: – Cable-like collagen protein • Ground substance: – Rich in proteoglycan complexes: • Contain hundreds of proteoglycan molecules: – Core protein with many hydrophilic carbohydrate chains attached.
    10. 10. The Extracellular Matrix (ECM) • Provides structural support. • More pliable (flexible) than the plant cell wall. • Helps cells adhere to each other.
    11. 11. The Extracellular Matrix (ECM) • The cell’s internal cytoskeleton is physically connected to the ECM via protein-protein interactions.
    12. 12. The Extracellular Matrix (ECM) • Specifically, actin filaments are linked to transmembrane proteins called integrins, which are linked to proteins (e.g. fibronectins and laminins) which are linked to collagen proteins.
    13. 13. Cell-Cell Interactions • The cell surface • The extracellular layer • Cell-cell connections – Cell-cell attachments – Cell-cell gaps • Cell-cell communication (long distance)
    14. 14. Cell-Cell Connections • Unicellular organisms may secrete polysaccharide-rich biofilms, connecting them to each other and to the substrate. – e.g. Dental plaque in your mouth!
    15. 15. Multicellularity Through Cell-Cell Connections • In multicellular organisms (e.g. plants and animals), various types cell-cell attachments and cell-cell gaps help to connect neighboring cells within a given tissue.
    16. 16. Cell-Cell Attachments • Middle lamella (plants) – Joins neighboring cell walls. • Tight junctions (animals) • Desmosomes (animals)
    17. 17. Middle Lamella (Plants) • Gelatinous polysaccharides (pectins) glue together neighboring plant cell walls.
    18. 18. Tight Junctions (Animals) • Specialized proteins from adjacent cell membranes line up and bind to each other, “stitching” the cells together.
    19. 19. Tight Junctions • Can form a watertight seal between cells. • Common in cells lining your skin, stomach, intestines, and bladder.
    20. 20. Desmosomes (Animals) • Anchoring and membrane proteins binding to each other and to intermediate filaments link the cytoskeletons of adjacent cells.
    21. 21. Desmosomes • Made of proteins that link the cytoskeletons of adjacent cells. • Common in epithelial and muscle cells.
    22. 22. Cadherins • A major class of cell adhesion proteins. • An important component of desmosomes. • Different types of cells express different types of cadherins on their plasma membranes. – Selective adhesion: adjacent cells of the same cell type often adhere to one another due to interactions of their cell-type specific cadherins.
    23. 23. Cell-Cell Interactions • The cell surface • The extracellular layer • Cell-cell connections – Cell-cell attachments – Cell-cell gaps • Cell-cell communication (long distance)
    24. 24. Cell-Cell Gaps • Create a direct connection between the cytoplasm of adjacent cells. • Allows neighboring cells to communicate directly through membrane “holes” and channels. • Two major types: – Plasmodesmata (plants) – Gap junctions (animals)
    25. 25. Plasmodesmata (Plants) • Cell-cell gaps connecting adjacent plant cells. • Lined with plasma membrane. • Allows a plant cell to directly share cytoplasm with neighboring plant cells.
    26. 26. Plasmodesmata (Plants) • Function in movement of water: – Speeds the movement of water from the root exterior to the root interior (location of xylem). • Function in movement of sugars: – Speeds the movement of sugars between adjacent phloem cells.
    27. 27. • Water, sugars, and other molecules can travel through plant tissues via the: – Symplastic route: • Traveling via the symplast (continuous network of shared cytoplasm between plant cells connected by plasmodesmata) – Apoplastic route: • Traveling around plant cells (e.g. through porous cell walls and the middle lamella) without actually entering the cytoplasm of individual cells. • Apoplast: Extracellular space around cells. Plasmodesmata (Plants)
    28. 28. Gap Junctions (Animals) • Each gap junction consists of many channels (made of _______) that connect adjacent ______ cells. • Allow water, ions, and small molecules to move between adjacent cells.
    29. 29. Gap Junctions (Animals) • Extensively found within _____ muscle tissue: – Speeds conduction of electrical impulses throughout the heart, coordinating heart muscle contraction (your heartbeat!). • Also found (to a limited extent) within ________ tissue: – Allow electrical impulses to directly flow from neuron to neuron.
    30. 30. Cell-Cell Connections: Summary ______ junctions __________ _____ junction
    31. 31. Cell-Cell Interactions • The cell surface • The extracellular layer • Cell-cell connections – Cell-cell attachments – Cell-cell gaps • Cell-cell communication (long distance)
    32. 32. Long Distance Communication • Distant cells communicate with each other via ________: – Information carrying molecules that: • Are secreted by a cell, • ________ in the body, and • Act on target cells far from the original cell. – ____ concentrations of hormones can have a large impact on target cells! – Hormone function and structure vary widely. • Lipid soluble (steroids) vs. non lipid soluble.
    33. 33. Hormone Signal Receptors • Signal receptors are ________ that change conformation (shape) upon hormone binding. • Each hormone binds to a specific type of signal receptor: – Steroid receptors: Located in ______. – Other hormone receptors: Located in cell ________. • To _______ to a particular hormone, a cell must express the appropriate signal receptor!
    34. 34. Steroid Hormone Receptors • ______ diffuses across plasma membrane and binds to receptor in cytosol. • Hormone-receptor complex can enter ______ and change gene activity.
    35. 35. Steroid Hormone: Estradiol • Estradiol, for example: – Is released by follicle cells in the _______ of females. – Binds to ________ within the ______ of various cell types, ultimately causing target cells to: • Differentiate (mammary gland cells during puberty). • Proliferate (endometrial cells lining the uterine wall). • Produce and secrete its own hormones (hypothalamic neurons).
    36. 36. Other Hormone Receptors • Non-lipid soluble (non-steroid) hormones bind to receptors on plasma ________. • Signal ____________: – Conversion of an extracellular signal (hormone) to an intracellular signal.
    37. 37. Signal Transduction Pathways • Involve several steps. • Message is _________ as it changes form.
    38. 38. Non-Steroid Hormone: Epinephrine • Epinephrine is a non-steroid hormone: – Produced and released by the _______ glands in response to short-term stress. – Binds to epinephrine ________ embedded in the cell membranes of liver cells: • Triggers a signal transduction cascade that ultimately activates phosphorylase: – Enzyme that helps convert glycogen to ________.
    39. 39. Signal Transduction Pathways • G-protein cascades: – Binding of hormone to receptor activates a _____ inside the cell, which then in turn activates other proteins inside the cell. – e.g. Epinephrine binding to epinephrine receptor on liver cell membranes. • Enzyme-linked receptor cascades: – Binding of hormone to receptor triggers a cascade of phosphorylation events inside cell. • Usually, the hormone-bound receptor is the first target to be phosphorylated. (Autophosphorylation) – e.g. _______ binding to insulin receptor on liver cell membranes.
    40. 40. G-Protein Cascades • G-protein initially in “___” conformation. • Signal (hormone) binds to _______.
    41. 41. G-Protein Cascades • Receptor changes _____ and activates. • G-protein activates (turns on) and ____.
    42. 42. G-Protein Cascades • Activated G-protein binds to and activates an _____. • Enzyme catalyzes formation of a ______ messenger. • Second messenger triggers a ______.
    43. 43. Second Messengers • ________ intracellular signaling molecules. • May open ion ______ or activate protein kinases. • Protein _______: – Enzymes that activate/inactivate other proteins by adding phosphate groups to them (phosphorylation).
    44. 44. Epinephrine Action • 1.) Epinephrine binds to and activates the epinephrine _______ on liver cell membranes. • 2.) Receptor activates an intracellular _______: – G-protein activates an enzyme, adenylyl cyclase. • 3.) Adenylyl cyclase catalyzes the formation of a second messenger, cyclic AMP (_______).
    45. 45. Epinephrine Action • 4.) cAMP activates the enzyme protein _____ A. • 5.) Protein kinase A activates phosphorylase kinase. • 6.) Phosphorylase kinase activates phosphorylase. • 7.) Activated phosphorylase catalyzes the cleavage of _______ into _______ monomers!
    46. 46. Enzyme-linked Receptors • Hormone binding to receptor results in autophosphorylation and __________ of receptor. • Activated receptors then induce phosphorylation of many other _______ in the cell: a phosphorylation cascade. • Cascade causes _________ of signal. • Best understood subgroup: – Receptor tyrosine kinases (RTKs)
    47. 47. Enzyme-linked Receptors
    48. 48. Enzyme-linked Receptors
    49. 49. Enzyme-linked Receptors Signal amplification!
    50. 50. Insulin Action • Insulin is a non-steroid hormone: – Released by the _______ in response to elevated blood glucose levels. – Binds to insulin _______ on the cell membrane of ______ cells: • Enzyme-linked receptors that initiate a “phosphorylation” cascade within the liver cell.
    51. 51. Insulin Action • 1.) Insulin binds to insulin receptor on liver cells. • 2.) Insulin ______ becomes phosphorylated. • 3.) _____ protein becomes activated. • 4.) Ras activates an ______ called MAPKKK. • 5.) MAPKKK activates another enzyme: MAPKK.
    52. 52. Insulin Action • 6.) MAPKK activates another enzyme: MAPK. • 7.) MAPK activates a transcription factor, which enters the ______. • 8.) Transcription factor increases the the expression of _______ involved in glycogen synthesis. • 9.) Liver synthesizes more _________ from glucose monomers.
    53. 53. Signal Transduction Pathways • Convert an extracellular signal to an intracellular signal. • Original message is __________ as it changes form. • May ultimately lead to the activation of: – Intracellular _______ – _________ factors – Membrane channels
    54. 54. Signal Deactivation • How are cell signals turned off? – Hormone ______ away from receptor. – G-proteins turn back “____” - deactivate. – Second messengers are degraded. – Phosphatases remove _______ groups from proteins.
    55. 55. Signal Transduction Pathways • As a biologist, you will encounter signal transduction pathways often, especially when studying: – The _______ system – The _______ system – The nervous system
    56. 56. Cell-Cell Interactions • The cell surface • The extracellular layer • Cell-cell connections – Cell-cell attachments – Cell-cell gaps • Cell-cell communication (long distance)
    57. 57. Review Questions • Contrast the extracellular matrix in animals versus the plant cell wall. • What are some different ways that neighboring cells can be joined to one another? • How do plasmodesmata differ from gap junctions?
    58. 58. Review Questions • How do steroid hormones differ from non-steroid hormones? • Draw out a G-protein signaling cascade. • Draw out an enzyme-linked receptor signaling cascade.

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