2.5 Biological membranes

• What role does cholesterol play in the cell membrane?

  Cholesterol adds structural stability and reduces cell fluidity.
• What is the function of the carbohydrate chains in glycolipids?

  The carbohydrate chains project into surrounding fluids, contributing to cell recognition and signaling.
• Where are glycoproteins found in the cell membrane?

  On the outer phospholipid monolayer
• What are glycoproteins?


  Proteins with carbohydrate chains attached that project into the surrounding fluid
• What type of proteins are integral proteins?

  Proteins embedded within the membrane
• Can you give an example of integral proteins?

  Channel proteins
• Where are peripheral proteins located in the cell membrane?

  On the inner or outer surface of the membrane
• What are the main types of proteins found in the cell membrane and their locations?

  • Glycoproteins: Found on the outer phospholipid monolayer
  • Integral proteins: Embedded within the membrane (e.g., channel proteins)
  • Peripheral proteins: Found on the inner or outer surface of the membrane
• What is the structure of the cell membrane primarily composed of?

  Phospholipid bilayer
• What does the fluid mosaic model describe?

  The movement of phospholipids, proteins, glycoproteins, and glycolipids in the membrane
• What is the role of extrinsic proteins in the cell membrane?

  Provide mechanical support and assist in cell recognition
• How do intrinsic proteins function in the cell membrane?

  They act as carriers or channels to transport molecules across the membrane
• What is the function of protein channels in the membrane?

  They form tubes that allow water-soluble ions to diffuse
• How do carrier proteins transport molecules?

  They bind with ions and larger molecules and change shape to transport them
• What is the role of cholesterol in the cell membrane?

  It restricts lateral movement and regulates fluidity
• How does temperature affect membrane fluidity?

  Increased temperature leads to more kinetic energy, increasing fluidity and permeability
• What happens to membrane structure at high temperatures?

  Carrier and channel proteins can denature, increasing permeability
• How do solvents affect the phospholipid bilayer?

  They can dissolve lipids, damaging the bilayer and increasing fluidity and permeability
• What is simple diffusion?

  Movement of molecules from high to low concentration until equilibrium is reached
• What types of molecules typically undergo facilitated diffusion?

  Ions and polar molecules that cannot diffuse freely
• What is osmosis?

  Movement of water from high water potential to low water potential across a partially permeable membrane
• What characterizes an isotonic solution?

  The kPa of the solution is the same as that of the cell
• What occurs in a hypotonic solution?

  Water moves from the solution into the cell, causing it to swell
• What is the result of a hypertonic solution on a cell?

  Water moves out of the cell, causing it to shrink
• What are the effects of hypertonic and hypotonic solutions on plant and animal cells?

  • Hypertonic (Plant): Plasmolysed
  • Hypertonic (Animal): Crenation
  • Hypotonic (Plant): Turgid
  • Hypotonic (Animal): Cytolysed
• What is active transport?

  Movement of molecules from lower to higher concentration using ATP and carrier proteins
• How does selective process work in active transport?

  Only certain molecules bind to the receptor site on carrier proteins
• What happens to ATP during active transport?

  ATP binds to the protein and is hydrolyzed into ADP and Pi
• What is the role of Pi in active transport?

  It causes the protein to change shape and release the molecule on the other side
• What is endocytosis?

  Bulk transport of molecules into a cell via vesicle formation
• What is phagocytosis?

  Endocytosis of solid particles
• What is pinocytosis?

  Endocytosis of liquid particles
• What is exocytosis?

  Bulk transport of molecules out of a cell via vesicle fusion
• What is required for exocytosis to occur?

  Energy from ATP to move the vesicle along the cytoskeleton
• What do digestive enzymes on the plasma membrane in the small intestine catalyze?

  The final breakdown of certain types of sugar
• Where do metabolic processes occur within a cell?

  Within the cell
• What is an example of a metabolic process that occurs in cells?

  Respiration
• What do the inner membranes of chloroplasts house?

  Chlorophyll
• What is the site of photosynthesis?

  The inner membranes of chloroplasts
• What are the roles of cell membranes?

  • Separates cell components from the external environment
  • Regulates transport of materials into and out of the cell
  • Contains enzymes involved in specific metabolic pathways
  • Releases chemicals that signal to other cells
  • Has antigens for immune system recognition