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Membrane structure & function

plasma membrane
1. has
  1. lipids
    1. a example is
      1. cholesterol
        helps modify the fluidity of the membrane over a range of temperatures
        is
        selectively permeable
        allowing only certain substances into the cell while keeping other out
  2. phospholipid bilayer
    1. is an
      1. amphipathic molecule
        has both a
        hydrophilic
        water loving
        naturally associate with
        polar water molecules
        require
        no energy to diffuse across membranes
        concentration gradient
        molecules move from an area where their concentration is high to an area where their concentration is low
        all proteins have
        channel proteins
        called
        aquaporins
        allow water to cross a membrane more quickly than expected
        allow
        cells to equalize water pressure difference
        movement of molecules from a higher to a lower concentration, that is down their concentration gradient until equilibrium is achieved
        is
        diffusion
        a
        solution
        contain both
        solute
        solid
        solvent
        liquid
        factors affection
        temp ,pressure, electrical currents and size
        as temp increases the rate of diffusion increases
        osmosis
        the diffusion of water across a selectively permeable membrane from low to high concentration
        always occurs
        from higher to lower concentrations
        osmotic pressure
        is
        pressure that develops in a system due to osmosis, causes a greater possibility that the water will diffuse in a specific direction
        isotonic solutins
        is
        solute concentration and water concentration both inside and out are equal
        tonicity
        strength of solution
        hypotonic solution
        are
        solutions that cause cells to swell or even burst due to intake of water
        the swelling of a plant in a hypotonic solution
        creates
        turgor pressure
        when the cytoplasm expands because the large central vacuole gains water and the plasma membrane pushes against the rigid cell wall
        plants wilt due to decreased turgor pressure
        hypertonic solution
        solutions that cause cells to shrink due to loss of water
        if placed in a hypertonic solution water leaves the cell
        if a plant is placed in solution the plasma membrane pulls away from the cell wall as the large central vacuole loses water
        this is an example of
        plasmolysis
        shrinking of cytoplasm due to osmosis
        polar molecules are chemically incompatible with the center of membrane and require expenditure of energy to drive their transport
        another transport is
        bulk transport
        is a way that large particles can exit or enter a cell
        a cell is selective about what enter by edocytosis
        facilitated transport
        allows
        the rate a which a solute crosses the plasma membrane to speed up by a carrier protein
        requires
        expenditure of energy because the molecules are moving down their concentration gradient
        active transport
        is
        transporting molecules against its concentration gradient
        requires
        energy
        proteins involved in active transport are called
        pumps
        proteins use energy to move a substance against it concentration gradient
        the transporter of sodium and potassium is called
        sodium-potassium pump
        has an initial shape that allows it to bind 3 sodium ions
        phosphate from an ATP molecule is added to the carrier protein and it changes shape, this shape change moves sodium across the membrane. the new shape is no longer compatible with binding to the sodium, falls away and binds with potassuim
        2 potassium and 3 sodium creates a solute gradient and electrical gradient
        hydrohobic
        water fearing
2. what makes one membrane different from another are the types of proteins integrated into the membrane
  1. embedded proteins
    1. are termed
      1. integral proteins
  2. proteins that occur only on the cytoplasmic side of the membrane
    1. are
      1. peripheral proteins
        occur on one surface or the other
        the 2 sides of membrane are not identical
        membrane is
        asymmetrical
  3. only
    1. animal cells
      1. have an
        extracellular matrix
        which contains
        various protein fibers and very large complex carbohydrate molecules
        leads
        eternal support to the plasma membrane to assisting in communications between cells
        when
        phospholipids and proteins have attached carbohydrate(sugar) chains
        is called
        glycolipids and glycoproteins
        occur outside the surface
        carbohydrate
        gives the cell
        a sugar coat
        its called
        glycocalyx
        protects cells and other functions
        each cell has its own finger print
3. model used to describe
  1. is the
    1. fluid-mosaic model
      1. flexible structure
        that states
        cells are pliable because phospholipid bilayer is fluid
        also
        the fluidity of the membrane prevents it form solidifying as external temperature drops
        the greater the concentration of unsaturated fatty acid residue the more fluid the bilayer
      2. is considered mosaic because of
        presence of many proteins
4. excoytosis
  1. an intracellular vesicle fuses with the plasma membrane as secretion occurs
    1. membrane of the vesicles becomes a part of the plasma membrane
      1. because
        both are nonpolar
  2. endocytosis
    1. cells take in substances by forming vesicles around the materials
      1. occurs in 3 way
        phagocytosis
        transports large substances
        cell eating
        pinocytosis
        transports small substances
        cell drinking
        receptor mediated endocytosis
        special form of pinocytosis
        selective and more efficent
5. junctions between cells
  1. are
    1. adhesion junctions
      1. serve to mechanically attach adjacent cells
        2 types
        desmosomes
        high flexible sheet of cells
        gap junction
        allows
        cells to communitcate
functions of proteins
1. channel protein
  1. allows a molecule to cross the plasma membrane, they form a channel that allows a substance to move from one side to the other
    1. cystic fibrosis, an inherited disorder is caused by a faulty chloride channel
  2. carrier protein
    1. interacts with a molecule so that it can cross the plasma membrane, they receive a substance and change their shape and this change serves to move the substance across the membrane
      1. without this carrier protein nerve impulse conduction would be impossible
    2. cell recognition protein
      1. are glycoproteins that help the body to recognize when it is being invaded by pathogens so that an immune response can occur
        without this recognition pathogens would be able to freely invade the body and hinder its function
      2. receptor protein
        have a shape that allow sonly a specific molecule to bind to it, binding the molecule causes the protein to change its shape and bring cellular response
        coordination of bodies organs is dependent on such signaling molecules
        enzymatic protein
        carry out metabolic reactions directly, catalyzes a specific reaction
        wouldn't be able to maintain a metabolism
        junction proteins
        tight junction join cells so that a tissue can fulfill a function, signaling molecules that pass through the plasma membrane allow cilia that line you respiratory tract to beat in unison
        embryo would have no nervous system

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	Created by kenzieaj14 about 9 years ago