Biological membranes

• What is the fluid mosaic model of membranes?

  A model describing membranes as a phospholipid bilayer with embedded proteins.
• What does the term "fluid" refer to in the fluid mosaic model?

  It refers to the phospholipid bilayer where individual phospholipids can move, giving the membrane a flexible shape.
• What does the term "mosaic" refer to in the fluid mosaic model?

  It refers to the extrinsic and intrinsic proteins of different sizes and shapes embedded in the membrane.
• What is the role of cholesterol in membranes?

  Cholesterol connects phospholipids and reduces fluidity, making the bilayer more stable.
• What is the role of glycolipids in membranes?

  Glycolipids are involved in cell signaling and cell recognition.
• What are the functions of extrinsic proteins in membranes?

  They serve as binding sites/receptors, antigens, bind cells together, and are involved in cell signaling.
• What are the functions of intrinsic transmembrane proteins in membranes?

  They function as electron carriers, channel proteins, and carrier proteins for facilitated diffusion and active transport.
• What are the functions of membranes within cells?

  They provide an internal transport system, are selectively permeable, provide a reaction surface, and isolate organelles for specific metabolic reactions.
• What are the functions of the cell-surface membrane?

  It isolates the cytoplasm from the extracellular environment, regulates transport of substances, and is involved in cell signaling and recognition.
• Name three factors that affect membrane permeability.

  Temperature, pH, and the use of solvents.
• How does temperature affect membrane permeability?

  High temperature denatures membrane proteins and increases the kinetic energy of phospholipid molecules, causing them to move further apart.
• How does pH affect membrane permeability?

  pH changes the tertiary structure of membrane proteins, affecting their function.
• How does the use of a solvent affect membrane permeability?

  Solvents may dissolve the membrane, increasing permeability.
• How can colorimetry be used to investigate membrane permeability?

  1. Use plant tissue with soluble pigment in vacuole; disrupt tonoplast and cell-surface membrane to increase permeability.
  2. Select colorimeter filter with complementary color.
  3. Use distilled water to set colorimeter to 0; measure absorbance/% transmission value of solution.
  4. High absorbance/low transmission indicates more pigment in solution.
• Define osmosis.


  Osmosis is the diffusion of water across semi-permeable membranes from an area of higher water potential to an area of lower water potential until equilibrium is established.
• What is water potential (ψ)?


  Water potential is the pressure created by water molecules, measured in kPa.
• What is the water potential of pure water at 25℃ and 100 kPa?

  The water potential of pure water at 25℃ and 100 kPa is 0.
• How does the presence of solute affect water potential?

  More solute results in a more negative water potential.
• How does osmosis affect plant cells?

  Osmosis into plant cells causes the protoplast to swell, making the cell turgid, while osmosis out causes the protoplast to shrink, making the cell flaccid.
• How does osmosis affect animal cells?

  Osmosis into animal cells can cause lysis, while osmosis out can cause crenation.
• Define simple diffusion.


  Simple diffusion is a passive process that requires no energy, involving the net movement of small, lipid-soluble molecules through the bilayer from high to low concentration.
• Define facilitated diffusion.


  Facilitated diffusion is a passive process where specific channel or carrier proteins transport large and/or polar molecules down the concentration gradient.
• How do channel proteins work?

  Channel proteins create hydrophilic channels that bind to specific ions, allowing one side of the protein to close while the other opens.
• How do carrier proteins work?

  Carrier proteins bind to complementary molecules, undergo a conformational change, and release the molecule on the other side of the membrane.
• What is active transport?

  Active transport is an energy-requiring process where ATP hydrolysis releases a phosphate group that binds to a carrier protein, changing its shape to transport molecules from low to high concentration.
• Define exocytosis.


  Exocytosis is an active process involved in bulk transport and transporting large particles, where vesicles fuse with the cell surface membrane.
• Define endocytosis.


  Endocytosis is an active process involved in bulk transport and transporting large particles, where the cell membrane engulfs substances.
• Name five factors that affect the rate of diffusion.

  Temperature, diffusion distance, surface area, size of molecule, and difference in concentration.