active transport

• active transport

  = movement of molecules into or out of a cell from a region of lower concentration to a region of higher concentration.

  • requires energy and carrier proteins.
  • energy is needed as the particles move up a concentration gradient.
  • carrier proteins span the membranes and act as 'pumps'
• 1. molecule to be transported binds to receptors in the channel of the carrier protein on the outside of the cell.
  2. on the inside of the cell ATP binds to the carrier protein and is hydrolysed into ADP and phosphate.
  3. binding of the phosphate molecule to the carrier protein causes the protein to change shape- opening up to the inside of the cell.
  4. the molecule is released to the inside of the cell.
  5. the phosphate molecule is released from the carrier protein and recombines with ADP to form ATP.
  6. the carrier protein returns to it's original shape.
• Bulk transport

  = form of active transport, large molecules like enzymes, hormones and whole cells like bacteria are too large to move through channel or carrier proteins, so they are moved into and out of the cell by bulk transport.
• examples of bulk transport

  -Endocytosis= bulk transport of material into cells. (Phagocytosis for solids and Pinocytosis for liquids) The cell surface membrane invaginates when it comes into contact with the material to be transported. The membrane then enfolds the material until the membrane fuses, forming a vesicle. The vesicles then pinches off and moves into the cytoplasm to transport the material further processing in the cell.

  -Exocytosis= reverse of endocytosis, vesicles move towards and fuse with the cell surface membrane, contents of vesicle released out cell