Biological Membranes

• What are the features of the phospholipid bilayer and what does it do?

  • Arranged in 2 layers with the phosphate head facing outside which is hydrophilic and fatty acid tails facing inward to one another which are hydrophobic
  • Allows lipid soluble molecules to enter the cells
  • Prevents water soluble substances leaving the cell
• What are features of integral proteins (instrinsic proteins) and what do they do?

  • Proteins that span the whole surface membrane.They generally act as carrier or channel proteins
  • They provide structural support for the cell
  • They also function as enzymes
• What are features of peripheral proteins (extrinsic) and what do they do?

  Features: Associated with the membrane surface, not embedded in lipid bilayer. Face outwards or inwards to cytoplasm of cell Function: Cell signaling, cell adhesion, enzymatic activity.
• What is the features and function of cholesterol?

  • Small compact molecules that embeds between the fatty acid tails of the bilayer.
  • It regulates the fluidity of the cell surface membrane by reducing the movement of phospholipds making membranes less fluid at RT
• What are the features and functions of glycolipids?


  • Generally phospholipids with brances carbohdyrate groups on their head.
  • The act as recognition sites, maintain the stablity of the cell surface membrane and help in cell adhesion
• What are the features and functions of glycoproteins?

  • Proteins with a branched carbohydrate group on their head.
  • They act as a recognition site, receptors and help in cell adhesion
• Whats the 'Fluid Mosaic Model'?

  • Describes the structure of the plasma membrane as a mosaic of componements
  • Mosaic- random pattern of proteins insterted into the phsophlipid bilayer
• Whats the role of internal membrane?

  • The internal membrane acts as protection for a cell
  • Contains a fixed environment inside the cell
  • Provides a transport system
  • Controls entry and exit of substances in membrane
• Whats the roll of the cell surface membrane?

  • Regulates the transport of materials entering and exiting the cells
  • Can act as enzymes to catalyse reactions
• Whats the definition of diffusion?

  • The movement of small, uncharged/ non-polar molecules from a high concentration to a lower concentration untill equilibrium occurs
  • Molecules diffsued directly across the phsopholipid bilayer
• Whats facillitated diffusion?

  • The movement of larger/uncharged molecules from a high concentration to a lower concentration untill equilibrium occurs
  • The method uses carrier or channel proteins to transport the molecule across the membrane
• What is active transport?

  • Active transport is the movement of molecules or ions across a cell membrane against their concentration gradient, requiring energy in the form of ATP.
  • Mainly ions transported by this method
• What is endocytosis?

  • Its the bulk movement of material into a cell by active means
  • Pinocytosis -Vesicles are formed
  • Phagocytosis -Bacteria into white blood cells
• What is exocytosis?

  • Its the bulk movement of material out of a cell
  • Vacuoles or vesicles fuse with the cell membrane and release material out of the cell#
  • Requires ATP
• Whats osmosis?

  • The movement of water from a region of high water potential to a region of lower water potential through a partially permeable membrane
  • The greater the number of water molecules present, the higher the water potential
  • 0kPa= pure distilled water
• What is hypotonic solution?

  • The move of dilute of two solutions
  • Higher water potential
• What is hypertonic solution?

  • The more concentrated of two solution
  • Lower water potential
• What is an isotonic solution?

  • A solution with the same water potential as another solution
• What are the water movements of the solutions?

  Hypotonic-cell becoming full of solution (turgid) may burst

  Hypertonic-cell is becoming shrivelled

  Isotonic-normal distribution of water in and out of cell at an equal rate