Cell Membrane

Passive Transport
1. Diffusion
  1. The net movement of ions or molecules from an area of higher concentration to an lower concentration.
  2. Molecules and ions are dissolved in the cytoplasm and extracellular fluid are in constant motion.
    1. This random motion causes a NET MOVEMENT from high to regions of low concentration.
  3. The major barrier to crossing the membrane is the hydrophobic interior
    1. That repels polar molecules but not non-polar barrier.
  4. movement in both directions can occur, but there is no NET change in either direction.
  5. Factors that affect rate of diffusion
    1. Molecule polarity
      1. small polar molecules cross membranes, their rates of diffusion are lower than those of non-polar molecules of the same size.
    2. Molecule Size
      1. Diffusion rate decreases with molecule size
      2. The larger the molcule, the harder it is to diffuse across the membrane.
    3. Molecule or ion charge
      1. Generally, charged molecules and ions cannot diffuse across a cell membrane.
    4. Temperature and Pressure
      1. High temperatures = more energy and move faster which increases the rate of diffusion.
      2. High pressures = are forced across the membranes and the rate of diffusion increases.
2. What is it?
  1. Movement of ions or molecules across a cell membrane from a region of higher concentration to lower concentration, without the input of energy.
3. What is a Concentration Gradient?
  1. A difference in concentration between one side of a membrane and the other
4. Osmosis
  1. The aqueous cytoplasm is a solvent for the molecules and ions.
  2. Cells interact with extracellular fluid which constantly changing.
    1. Too much water enters, it swells
    2. Too much water leaves the cell, it shrinks.
    3. Regulating the water entry is crucial to cells.
  3. What is it?
    1. The movement of WATER from an area of higher concentration to low, across a semi-permeable membrane.
      1. Cells must maintain enough water to enable cellular processes.
      2. H2O molecules move because the membrane is impermeable to the solute and concentration can differ on either side of the cell.
  4. Concentration of solutes determines the OSTOMIC CONCENTRATION
    1. same concentration in both the concentration is ISOTONIC
    2. the solution with low concentration is HYPOTONIC
    3. 2 solutions have unequal C, the solution with higher is HYPERTONIC
  5. A process in which the water molecules enter the cell.
5. Facilitated Diffusion
  1. Carrier Proteins
    1. What is it?
      1. A membrane protein that BINDS to and transports one or more particles of substance from one side of the membrane to the other.
    2. Transport larger molecules such as Amino acids and glucose
    3. Structure
      1. Due to the binding, only a few molecules can cross.
      2. Have low rate of diffusion compared to channel proteins
      3. Interior is lined in Amino acids that bind to particles to be transported.
    4. Malfunctions can cause diseases; painful stones (inability to remove cystine and amino acids from urine.
  2. Channel Proteins
    1. Some remain open all the time while others have gates that open or close.
      1. Different types of gates that open or close in response to signals, hormones,pressure or light.
    2. What is it?
      1. A membrane protein that forms a channel across the cell membrane to allow specific particles to cross
    3. Structure
      1. Exterior composed of amino acids with non-polar side chains
      2. composed of amino acids and have polar, polar or charged side chain
      3. Tubular shaped
      4. Non-polar interior of the cell anchors the protein in place
        Hydrophillic interior
    4. Transport small polar molecules
  3. What is it>
    1. The transport of ions or molecules across a membrane protein along the concentration gradient of that ion or molecule.
      1. For those molecules that cannot easily cross the plasma membrane
  4. Occurs only if there is higher concentration of the molecule oustide than the inside of the cell
  5. Glucose enters the intestinal lining through the channels on the membrane of the cell.
    1. Then exit from the other side and into the blood stream.
      1. Occurs due to Facililated difusion
Active Transport
1. Membrane Assisted Transport
  1. a method to move materials that are too large molecules across the cell
  2. Exocytosis
    1. A transport method in which the vesicle fuses with the membrane and releases its contents
      1. The vesicle can release hormones, neurotransmitter, waste and much more.
  3. Endocytosis
    1. a process in which the cell membrane engulfs extracellular material and bring it inside the cell
    2. Phagocytosis
      1. endocytosis involving solid particles
    3. Pinocytosis
      1. endocytosis involving liquid particles
    4. Receptor-mediated endocytosis
      1. use of receptor proteins on a portion of the membrane to bind with specific molecules outside the cell
  4. Still using ATP
2. What is it?
  1. Substances move up or against the concentration gradient with the input of ATP
    1. ATP is the main source of energy in the cell.
      1. Use of ATP can be DIRECT (Primary Active Transport) and INDIRECT (secondary active transport).
3. Primary Active Transport
  1. What is it?
    1. A process that uses ATP directly to move molecules or ions one side of the membrane to the other
      1. Use of Carrier Proteins
  2. Na+/K+ Pump
    1. What is it?
      1. A mechanism that uses ATP to reset the Na+ and K+ ions after a nerve impulse
    2. ATP breaks down to ADP in order to pump 3 Na+ out, and 2 k+ in
      1. E2 CONFORMATION: NA+ IONS
        E1 CONFORMATION: K+ IONS
      2. Phosphate from ATP is covalently attached to the carrier protein
        An important protein for animal cells, it allows the transfer of Na+ and k+ ions in and out of cell membrane
  3. Types of transportation for molecules
    1. Symport
      1. Tranports the solute and a cotransported solute at the same time and direction
    2. Uniport
      1. Transports only one solute at a time
    3. Antiport
      1. Transports the solute and the co-transported solute in the opposite directions
        One goes in, the other goes out
4. Secondary Active Transport
  1. What is it
    1. A process that uses ATP indirect to move molecules or ions thr
What is it?
1. It maintains the integrity of the cell by regulating the passage of ions in and out of the cells.
2. It's functions?
  1. The primary function is to protect thecell from its surrondings and it consists of Phospholipid bilayer.
    1. What is a Phospholipid Bilayer?
      1. A double layer of phospholipid molecules that line up tail to tail to create a hydrophillic cell membrane.
      2. Fluid Mosaic Model?
        A model which explains the structure of functional cell membrane and the pattern of protein molecules in a fluid phospholipid layer
        Each layer is called a Leaflet--> a membrane bilayer composed of various macromolecules.
        They act like scaffolding in which proteins and macromolecules are embedded.
        Held together by weak INTERmolecular forces
      3. The Fluidiity of Phospholipid Bilayer
        If too fluid --> bilayer permits too many molecules to diffuse in and out of the cell.
        If less fluid --> bilayer prevents too many molecules from crossing.
        Factors that affect fluidity:
        Fatty acid length "tail"
        Long tails--> more intermolecular attractions and hold together more tightly compared to the short tails.
        Common length of the fatty acid is 16 or 18 carbon atoms.
        Presence of double bonds in the fatty acid "tails"
        Double bond forms "kinks" in the tail. The presence of one or more double bond causes tails to be less tightly packed and more fluid.
        Temperature
        If temperature rises, unable to act as a barrier
        If temperature sinks, it solidifies into a gel state.
      4. The function of properties in a Phospholipid Bilayer
        Proteins associated with membranes are: Integral or Peripheral Proteins
        Integral proteins
        The proteins are embedded in the membrane
        Proton Pump
        A integral membrane protein that moves protons (H+) across the membrane during oxidation reactions
        The protons move out, and cause a C gradient
        So, they come into the cytoplasm through an enzyme, ATP Synthase
        Enzyme uses the energy from the movement and makes ADP --> ATP.
        The enzyme is a channel, but uses ATP
        Peripheral Proteins
        The proteins are more loosely and temporaily attached to outer regions of the membrane or to integral proteins.
        Membrane proteins help determine the function of the membrane by:
        Reaction catalysis
        Enzymes in the cell membranes carry out chemical reactions.
        Cell recognition
        The carbohydrate chains that protrude from glycoprotein on the outer layer of the cell membrane enable cells to recognize each other.
        It allows the cell to identity the harmful intruders --> bacteria.
        Transport
        Play an important role in transporting substances across the cell membrane
        Signal reception and transduction
        Receptor proteins in the membrane bind to signal molecules such as, hormones and change shape as a result.
        Intiateing a cellular response to signal, enabling the cells to recieve and respond to signals from the brain and the other organs.
        They help stabilize the membrane and hold them in place by linking them with the cytoskeleton of the cell.
      5. If a group of phospholipid are put in water, micelle is formed.
        Micelle are lipid molecules that arrange themselves making a circle in aqueous solutions
        Lipids are HYDROPHOBIC
        A class of proteins, that has CARB groups attached to polypeptide chain is called GLYCOPROTEIN
Ions, molecules, and macro-molecules are impermeable. Along with H2O.
Na+/K+ pump Continued
1. Action Potential is associated with the passage of nerve impulses along the membrane
  1. Nerve sends impulses for this action to occur
  2. Depolarization
    1. Opening of voltage gated Na+ channels
  3. Replorization
    1. Closure of Na+ and opening of K+, voltage gated channels
  4. Resting Potential stages
    1. Voltage gated K+ channels remain open after the potential reaches rest level
      1. Rest state @ -90
  5. This pump requires ATP
  6. When an action potential starts, it moves along an axon automatically.
Calcium pump
1. Powered by ATP.
  1. Active Transport
2. When the signal is released, Ca releases from Sacroplasmic Reticulum
  1. Spread and attach to Tropmyosin on the actin filaments
    1. Will contract so until Ca is removed.
3. Transfers Ca after a muscle contracts
  1. Is a transport protein

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	Created by simran97 about 9 years ago