4.4 - Active Transport

• active transport

  the movement of molecules or ions into or out of a cell against a concentration gradient using ATP and carrier proteins
• direct active transport

  molecule attaches to carrier protein on membrane

  ATP binds to protein and is hydrolysed into ADP and Pi (inorganic phosphate) releasing energy which causes protein to change shape and open on the opposite side of the membrane releasing molecule

  Pi is released from protein so it goes back to its original shape so process can be repeated
• use of ATP in active transport

  directly move molecules

  individually move molecules using a concentration gradient that has been set up by direct active transport
• differences between active transport and facilitated diffusion

  active transport uses energy in the form of ATP, facilitated diffusion is a passive process

  in active transport molecules are moved against a concentration gradient, in facilitated diffusion it moves down a concentration gradient
• similarities between active transport and facilitated diffusion

  both use carrier proteins

  both are very selective in the substances being transported
• factors affecting rate of active transport

  speed of individual carrier proteins: the faster they work the faster the rate of active transport

  number of carrier proteins: the more there are the faster the rate of active transport

  rate of respiration and ATP availability: energy is required so if respiration is inhibited so active transport can't take place
• how decreasing the concentration gradient affect rate of active transport

  won't have an impact because molecules and ions are being moved against their concentration gradient
• bulk transport

  a type of active transport that involves the intake of larger molecules
• types of bulk transport

  endocytosis: substances move into cells

  exocytosis: removing substances from cells
• receptor mediated endocytosis

  receptor molecules on cell membrane bind with specific substance from extracellular environment

  surface folds inwards until a coated vesicle separates from the cell surface membrane