Module 2

cell mediated transport = movement of molecules across a cell membrane by transport protein

Transport Proteins

Types:
- channel- creates open, water-filled pores
- gated channel- channel that opens and closes under various conditions
- carrier- binds to substrate and undergoes a conformational change to move substrates across the membrane
- ATPase pump- uses ATP as an energy source to trigger the conformational change to move the substrates across the membrane
- # of substrates
- uniporter- moves one type of molecule
- cotransporter- moves more than one type of molecule per cycle
  - symporter- same direction
  - antiporter- opposite directions
- direction
- unidirectional- only works in one direction
- bidirectional- works in either direction
- number and directional terms are NOT mutually exclusive
  - uniporter does not = unidirectional always and can be unidirectional or bidirectional
  - cotransporter can move one direction or both direction
  - uniporter CANNOT be a cotransporter
  - unidirectional CANNOT be bidirectional
competition for specificity in transport proteins
- concentration gradient can effect multiple molecules with the same active site

facilitated diffusion
- cell mediated diffusion
- passive process that relies on the concentration gradient
- binding of the substrate will cause the transporter to undergo conformational change
primary (1) active transport
- uses ATP as an energy source so it does not rely on the concentration gradient
  - can pump against the gradient
Na+/K+
- 2 K+ in and Na + out
- utilizes 1 ATP
- lacking one component prevents operation
- must be in correct location
- can go with or against
secondary (2) active transport
- cotransporter using the concentration gradient of one molecule as the energy source to move a second molecule
- one molecule is moving high to low and the other from low to high concentration
- primary active transport must’ve occurred to establish the concentration gradient