Biological membranes

• What is a glycolipid?

  A phospholipid with carbohydrate chain
• What is a glycoprotein?

  Protein with a carbohydrate chain
• Why are cell membranes described as partially permeable barriers?

  They allow some molecules to pass through
• What does permeability refer to in cell membranes?

  Ability to let substances pass through
• How do small molecules pass through the cell membrane?

  They diffuse through structural molecules
• What role do special protein channels play in cell membranes?

  They allow specific substances to pass through
• What determines the permeability of a cell membrane?

  Properties of the component molecules
• What are the roles of the plasma membrane at the surface of cells?

  • Separates cell components from the environment
  • Regulates transport of materials
  • Contains enzymes for metabolic pathways
  • Has antigens for immune recognition
  • Releases signaling chemicals
  • Site for cell communication
  • May be site of chemical reactions
• What is the function of membranes around organelles in eukaryotic cells?

  • Separate organelle contents from cytoplasm
  • Allow organelles to perform specific functions
  • Some metabolic processes occur on membranes
• What are cristae in mitochondria?

  Folded inner membranes for reactions
• What do thylakoid membranes in chloroplasts contain?

  Chlorophyll for photosynthesis reactions
• How does the fluid mosaic model describe cell membrane structure?

  Phospholipid bilayer with floating proteins
• What is the role of cholesterol in cell membranes?

  Regulates fluidity and stability
• What is the thickness of a cell membrane?

  Between 5 and 10 nm
• What is the glycocalyx?

  Carbohydrate chains on the membrane surface
• How do cell membranes differ in composition?

  • Differentiated and specialized cells have unique proteins
  • Neurones have channels for ion conduction
  • Myelin sheath has high lipid content
  • White blood cells have receptors for antigens
• What is the protein composition of mitochondria's inner membranes?

  76% protein and 24% lipid
• What is diffusion?

  Movement from high to low concentration
• What is facilitated diffusion?

  Movement across a membrane via protein channels
• Why do cells need to receive raw materials?

  • To sustain biochemical processes
  • To produce ATP for energy
  • To remove toxic waste products
  • To export signaling molecules
• What happens when molecules reach equilibrium during diffusion?

  They remain evenly dispersed, no more diffusion
• What is simple diffusion?

  Free movement of molecules in a medium
• How do small molecules like oxygen pass through membranes?

  By simple diffusion through the membrane
• What are aquaporins?


  Specific water channel proteins in membranes
• How is the concentration gradient maintained in cells?

  • Molecules enter cells and pass into organelles
  • Oxygen is used in aerobic respiration
  • Carbon dioxide diffuses into plant cells
• What is the role of aquaporins in cell membranes?

  They allow water to cross the membrane.
• Why can water diffuse through the phospholipid bilayer despite being polar?

  Because water is present in high concentrations.
• How does oxygen maintain the concentration gradient in cells?

  It diffuses into mitochondria for respiration.
• What happens to carbon dioxide in palisade mesophyll cells?

  It diffuses into chloroplasts for photosynthesis.
• What factors affect the rate of simple diffusion?

  • Temperature: Higher temperature increases diffusion rate.
  • Diffusion distance: Thicker membranes slow diffusion.
  • Surface area: Larger areas increase diffusion.
  • Size of molecule: Smaller molecules diffuse faster.
  • Concentration gradient: Steeper gradients increase diffusion speed.
• What is facilitated diffusion?

  Diffusion through protein channels in membranes.
• How do glucose molecules cross the plasma membrane?

  They bind to carrier proteins for transport.
• Why can't ions diffuse through the lipid bilayer?

  They are insoluble in lipid due to polarity.
• What is the diameter of protein channels used in facilitated diffusion?

  About 0.8 nm in diameter.
• How do neurone plasma membranes facilitate nerve impulse conduction?

  They have specific channels for sodium and potassium ions.
• What role do chloride ion channels play in epithelial cells?

  They regulate mucus composition in airways.
• How does the addition of solute molecules affect water potential?

  It lowers the water potential of the solution.
• What is osmosis?

  Diffusion of water across a partially permeable membrane.
• What happens to water potential when solute molecules dissociate?

  It decreases as more particles are created.
• What occurs when cells are placed in a solution with higher water potential?

  Water enters the cells by osmosis.