II. D. 2 - Cell Membrane: Transport

• Plasma membrane - boundary that separates the living cell from the surroundings
• Structure of the plasma membrane

  1. Phospholipid bilayer
  2. Hydrophilic head
  3. Hydrophobic tail
  4. Chain of fatty acids
  5. Cholesterol
  6. Protein
• Function of proteins

  1. Transport
  2. Enzymatic Activity
  3. Signal transduction
  4. Cell-cell recognition
  5. Intercellular jointing
  6. Attachment to the extracellular matrix (ECM)
• Permeability guidelines of the lipid bilayer

  1. Hydrophobic/nonpolar - rapidly dissolves in the lipid bilayer
  2. Hydrophilic/polar - doesn't dissolve easily
• Types of protein regions

  1. Integral - Penetrate the hydrophobic core
  2. Peripheral - Surface
  3. Transmembrane - spans the membrane
• Transport proteins

  1. Carriers - bind molecules and changes shape
  2. Channel - hydrophobic channel that acts as a tunnel
  3. Aquaporins - facilitate the passage of water
• Transport of macromolecules via packaging in vesicles

  1. Endocytosis - forms vesicles to take in molecules
  2. Exocytosis - secretion of molecules by fusion of vesicles with the plasma membrane
• Transports:

  1. Passive transport - diffusion of a substance across a membrane with no energy investment from a high to low solute concentration
  2. Osmosis - movement of water from a low to high solute concentration
  3. Active transport - requires ATP to transport molecules
  4. Facilitated diffusion - involves transport proteins that speed passive movement
  5. Channel - aquaporins and ion channels
  6. Carrier
• Environments based on osmosis

  1. Hypertonic - low solute concentration in the cell (shrivel)
  2. Isotonic - equal solute concentration out of the cell
  3. Hypotonic - high solute concentration in the cell (burst)
• Phagocytosis - cell engulfs a particle in a vacuole and fuses with a lysosome for digestion

  Pinocytosis - molecules are taken up when extracellular fluid is gulped into tiny vesicles
• Bulk transport systems:

  1. Exocytosis - transport vesicles from the golgi apparatus to the plasma membrane to fuse and release content
  2. Endocytosis - Entrance of content via vesicles
  3. Receptor-mediated - binding of ligands to receptors trigger vesicle formation