Cell membranes and transport

• What are the principle components of the plasma membrane?


  Intracellular and extracellular proteins, Glycoproteins, Phospholipids, Cholesterol
• What is the fluid-mosaic model?


  A model that describes membrane structure as a 'sea' of mobile phospholipids studded with various proteins.
• What are intrinsic proteins?


  Proteins found within the phospholipid bilayer. Includes channel and carrier proteins.
• What are the functions of intrinsic proteins?


  Structural support, Carry water-soluble molecules across the phospholipid bilayer, Form ion channels to enable active transport
• What are extrinsic proteins?


  Proteins found at the edges of the phospholipid bilayer.
• What are the functions of extrinsic proteins?


  Receptors, Act as antigens, enabling cell recognition, Help cells adhere to each other
• What is glycocalyx?


  A glycoprotein and glycolipid coating surrounding the cell membrane of some cells.
• What factors affect the permeability of the plasma membrane?


  Temperature, Organic solvents, pH
• How does temperature effect permeability?


  As temperature increases, the phospholipids have more kinetic energy and move more, increasing the fluidity and permeability of the plasma membrane.
• How does high temperature effect the plasma membrane?


  Channel and carrier proteins will become denatured, affecting membrane permeability. The cell will eventually break down completely.
• How do organic solvents effect permeability?


  Organic solvents dissolve membranes, disrupting cells. This increases the fluidity and permeability of the plasma membrane.
• What is diffusion?


  The passive movement of small non-polar, lipid-soluble molecules from an area of high concentration to an area of low concentration.
• What factors affect the rate of diffusion?


  Temperature, Steepness of concentration gradient, Size of molecule, Diffusion distance, Surface area
• What is osmosis?


  The passive diffusion of water molecules from a region of high water potential to a region of lower water potential (down a water potential gradient) through a selectively permeable membrane.
• What is water potential (Ψ)?


  A measure of the tendency of water molecules to move from one area to another.
• What is incipient plasmolysis?


  The effect produced by placing plant cells in an isotonic solution. Causes the cell membrane to pull away from the cell wall in some areas. The cell is neither plasmolysed nor turgid.
• What is facilitated diffusion?


  The net movement of substances from a high concentration to a lower concentration (down their concentration gradient) through transport proteins without the use of energy.
• What is an example of facilitated diffusion?


  Co-transport
• What is active transport?


  The movement of substances from a low concentration to a higher concentration (against the concentration gradient) through carrier proteins with the use of energy in the form of ATP.
• How does cyanide effect active transport?


  Cyanide inhibits cytochrome oxidase, stopping the production of ATP. This prevents active transport.
• What are the mechanisms of bulk transport?


  Endocytosis, Exocytosis
• What is endocytosis?


  The bulk uptake of substances into a cell by invagination of the membrane to form a vesicle. Uses energy in the form of ATP.
• What types of endocytosis are there?


  Phagocytosis, Pinocytosis
• What is pinocytosis?


  The bulk uptake of liquids into the cell using energy in the form of ATP.
• What is phagocytosis?


  The bulk uptake of solids into the cell using energy in the form of ATP.
• What is exocytosis?


  The bulk transport of substances out of a cell via a vesicle that fuses with the plasma membrane. Uses energy in the form of ATP.