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 10 11 105 fa13 cell cell interactions skel Presentation Transcript

  • Cell-Cell Interactions Dr. Corl BIOL 105 September 13, 2013
  • Cell-Cell Interactions • The cell surface • The extracellular layer • Cell-cell connections – Cell-cell attachments – Cell-cell gaps • Cell-cell communication (long distance)
  • 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!
  • 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.
  • 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.
  • The Plant Primary Cell Wall • Fibrous components = Cellulose microfibrils. • Ground substance = Pectins and other gelatinous polysaccharides.
  • 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).
  • 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!
  • 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.
  • The Extracellular Matrix (ECM) • Provides structural support. • More pliable (flexible) than the plant cell wall. • Helps cells adhere to each other.
  • The Extracellular Matrix (ECM) • The cell’s internal cytoskeleton is physically connected to the ECM via protein-protein interactions.
  • 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.
  • Cell-Cell Interactions • The cell surface • The extracellular layer • Cell-cell connections – Cell-cell attachments – Cell-cell gaps • Cell-cell communication (long distance)
  • 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!
  • 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.
  • Cell-Cell Attachments • Middle lamella (plants) – Joins neighboring cell walls. • Tight junctions (animals) • Desmosomes (animals)
  • Middle Lamella (Plants) • Gelatinous polysaccharides (pectins) glue together neighboring plant cell walls.
  • Tight Junctions (Animals) • Specialized proteins from adjacent cell membranes line up and bind to each other, “stitching” the cells together.
  • Tight Junctions • Can form a watertight seal between cells. • Common in cells lining your skin, stomach, intestines, and bladder.
  • Desmosomes (Animals) • Anchoring and membrane proteins binding to each other and to intermediate filaments link the cytoskeletons of adjacent cells.
  • Desmosomes • Made of proteins that link the cytoskeletons of adjacent cells. • Common in epithelial and muscle cells.
  • 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.
  • Cell-Cell Interactions • The cell surface • The extracellular layer • Cell-cell connections – Cell-cell attachments – Cell-cell gaps • Cell-cell communication (long distance)
  • 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)
  • 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.
  • 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.
  • • 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)
  • 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.
  • 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.
  • Cell-Cell Connections: Summary ______ junctions __________ _____ junction
  • Cell-Cell Interactions • The cell surface • The extracellular layer • Cell-cell connections – Cell-cell attachments – Cell-cell gaps • Cell-cell communication (long distance)
  • 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.
  • 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!
  • Steroid Hormone Receptors • ______ diffuses across plasma membrane and binds to receptor in cytosol. • Hormone-receptor complex can enter ______ and change gene activity.
  • 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).
  • 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.
  • Signal Transduction Pathways • Involve several steps. • Message is _________ as it changes form.
  • 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 ________.
  • 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.
  • G-Protein Cascades • G-protein initially in “___” conformation. • Signal (hormone) binds to _______.
  • G-Protein Cascades • Receptor changes _____ and activates. • G-protein activates (turns on) and ____.
  • G-Protein Cascades • Activated G-protein binds to and activates an _____. • Enzyme catalyzes formation of a ______ messenger. • Second messenger triggers a ______.
  • 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).
  • 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 (_______).
  • 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!
  • 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)
  • Enzyme-linked Receptors
  • Enzyme-linked Receptors
  • Enzyme-linked Receptors Signal amplification!
  • 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.
  • 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.
  • 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.
  • 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
  • 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.
  • Signal Transduction Pathways • As a biologist, you will encounter signal transduction pathways often, especially when studying: – The _______ system – The _______ system – The nervous system
  • Cell-Cell Interactions • The cell surface • The extracellular layer • Cell-cell connections – Cell-cell attachments – Cell-cell gaps • Cell-cell communication (long distance)
  • 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?
  • 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.