cell membrane

• Bubbles and cell membranes

  • Fluid
  • Flexible
  • Can self-repair
• Cell membrane


  Thin, flexible barrier that surrounds all cells
• Plant cells


  • Also produce a strong supporting layer around the membrane known as a cell wall
• Cell (plasma) membrane


  Boundary that separates the cell from its environment and needs to be penetrable to allow things to go in and out
• Things that go in and out of the cell

  • IN: food, carbohydrates, sugars, proteins, amino acids, lipids, salts, O2, H2O
  • OUT: waste, ammonia, salts, CO2, H2O, products
• Phospholipid bilayer


  Makes up the cell membrane, with polar hydrophilic heads and nonpolar hydrophobic tails
• Functions of the cell membrane

  • Protective barrier
  • Regulates transport in & out of cell (selectively permeable)
  • Provides anchoring sites for filaments of cytoskeleton
  • Provides a binding site for enzymes
  • Interlocking surfaces bind cells together
  • Allows cell recognition
  • Contains the cytoplasm
• Fluid Mosaic Model


  Cell membranes consist of a structural framework of phospholipid molecules that is embedded with proteins, steroids, glycoproteins, and glycolipids that can flow around the surface of the cell within the membrane
• Embedded proteins


  Can be hydrophilic, with charged and polar side groups, or hydrophobic, with nonpolar side groups
• What molecules can get through the membrane directly

  • CAN pass through: Small molecules, Lipids (nonpolar), Gases (N2, CO2, O2)
  • CANNOT pass through: Large molecules, Charged molecules, Hydrophilic, Sugars, Na+, Cl-, H2O (passes through in small amounts, mainly enters the cell by aquaporin)
• Osmosis


  A special form of diffusion where the fluid/solvent moves, not the particles/solute
• Types of cell transport

  • Passive Transport: Simple, Osmosis, Facilitated (no energy needed, movement down concentration gradient)
  • Active Transport: Endocytosis, Exocytosis, Na/K Pump (requires energy/ATP, movement against concentration gradient)
• Passive transport


  Movement from high to low concentration, no energy needed, goes to equilibrium
• Active transport


  Movement from low to high concentration, requires energy (ATP), against the concentration gradient
• Diffusion of liquids


  Movement from high to low concentration, passive process with no energy used
• Facilitated diffusion


  Moves molecules from high to low concentration through a protein channel/tunnel, uses transport proteins, still no energy/ATP involved, selective for what goes through
• Osmosis


  Diffusion of water across a membrane, only water moves, from low solute to high solute
• Osmotic conditions


  • Hypertonic - more solute, less water, higher concentration
  • Hypotonic - less solute, more water, lower concentration
  • Isotonic - equal solute, equal water, equal concentration
• Active transport


  Requires energy (ATP), examples include Na/K pump, moves materials from low to high concentration
• Endocytosis


  Takes in macromolecules and forms new vesicles, includes phagocytosis (cellular eating) and pinocytosis (cellular drinking)
• Exocytosis


  Vesicles fuse with cell membrane and expel contents, releases things from the cell