Biological membranes

• What is the structure of biological membranes?


  • Composed of a sea of phospholipids
  • Protein molecules are interspersed
  • Partially permeable membrane
• What is the main function of biological membranes?


  • Control movement of substances in and out of cells/organelles
  • Contains receptors for hormones
  • Enables adjacent cells to stick together
• What is the fluid mosaic model?


  • Describes the structure of the cell membrane
  • Fluidity of the membrane
  • Mosaic arrangement of proteins
• What is the arrangement of phospholipids in the cell membrane?


  Hydrophilic heads point outwards and hydrophobic tails point inwards
• What are the roles of proteins in the cell membrane?


  • Aid movement across the membrane
  • Provide mechanical support
  • Act as receptors with glycolipids
• What is the role of cholesterol in the cell membrane?


  • Makes the membrane more rigid
  • Reduces lateral movement of phospholipids
  • Prevents leakage of water and ions
• What are glycolipids and their function?


  • Carbohydrates bound to lipids
  • Act as cell surface receptors
  • Allow cells to adhere to form tissues
• What are glycoproteins and their function?


  • Carbohydrates attached to extrinsic proteins
  • Act as cell surface receptors and neurotransmitters
  • Allow cells to recognize one another
• What are the types of movement through cell membranes?

  • Diffusion
  • Facilitated diffusion
  • Osmosis
  • Active transport
  • Exocytosis and endocytosis
  • Co-Transport
• What is diffusion?


  Passive movement of small, non-polar, lipid-soluble molecules from high to low concentration
• What is facilitated diffusion?


  Movement of polar and charged molecules through channel proteins
• What is osmosis?


  Diffusion of water molecules from high water potential to low water potential
• What is active transport?


  Transport of molecules from low to high concentration using energy (ATP)
• What is exocytosis and endocytosis?


  • Exocytosis: transport of large particles out of the cell
  • Endocytosis: transport of large particles into the cell
• What is co-transport?


  Movement of substances using ions to facilitate transport across membranes
• How does the rate of gas exchange by diffusion increase?


  As the surface area increases and diffusion distance decreases
• What process requires energy in the form of ATP?


  Active transport
• What are the main differences between exocytosis and endocytosis?


  • Endocytosis transports large particles into the cell using vesicles.
  • Exocytosis releases large particles from the cell by fusing vesicles with the cell membrane.
• What is co-transport primarily associated with in epithelial cells?


  Movement of ions and substances
• How do sodium and potassium ions contribute to co-transport in epithelial cells of the ileum?


  Sodium and potassium ions are pumped out, creating a concentration gradient that facilitates the movement of glucose and amino acids.
• What factors increase the rate of gas exchange by diffusion?


  • Increased surface area
  • Decreased diffusion distance
  • Steeper diffusion gradient
  • Increased temperature