Active Transport

• Active transport

  This is the active movement of ions or polar molecules from a lower concentration to a higher concentration using a carrier protein. This movement against the concentration gradient requires energy from ATP. Since the ATP is produced in respiration, oxygen is also required. 
• Molecules move against a concentration gradient.
• Energy from ATP is required.
• Specific protein carriers are required- they change shape to move substances from one side of the membrane to the other.
• Carrier proteins act as pumps. Their shape is specific and complements the shape of the molecule they carry.
• Carrier proteins carry larger or charged molecules through the membranes as they cannot diffuse through the lipid bilayer. 
• Molecules that are actively transported by carrier proteins:

  • Non-lipid soluble  
  • Large & water soluble (polar molecules) 
  • Ions 
• ATP changes the shape of the carrier protein in active transport and hence on one side of the membrane the shape of the protein will complement the specific molecule to be transported. Once energy has been used by the protein carrier it changes shape and releases the specific molecule. This ensures one way flow. 
• Anything that inhibits the production of ATP will prevent the movement of molecules by active transport. For example, cyanide is a respiratory inhibitor that prevents the production of ATP.
• Glucose is absorbed from the lumen of the ileum by co transport.
• Co transporters are a type of carrier protein. They bind two molecules at a time. The concentration gradient of one molecule is used to move the other molecule against its own concentration gradient.
• The epithelial cells lining the ileum have microvilli, finger like projections to increase the surface area. They also have an increased number of protein channels and carrier molecules in their membranes.
• 1. Sodium ions actively transported out of the epithelial cells of the ileum, into the blood by the sodium-potassium pump.
• 2. Concentration gradient of sodium ion is created- the concentration is lower in the epithelial cell and higher in the lumen of the ileum.
• 3. Sodium ions diffuse from the lumen into the epithelial cell, down the concentration gradient, via the sodium-glucose co-transporter proteins. Glucose is co-transported into the cell via the protein.
• 4.The concentration of glucose is higher in the epithelial cell than in the blood, so glucose diffuses down the concentration gradient through a protein channel by facilitated diffusion.