10 11 105 fa13 cell cell interactions skel
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.