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Passive Transport
PASSIVE TRANSPORT
- Requires no energy input because all molecules still move down their concentration gradient
- All channels and many transporters work via passive transport
- Somewhat specific, only allowing a molecule through if it is the right size and charge
- Allow for faster transport than transporters or diffusion
- Some channels require a signal before solutes can travel through
- Aquaporins are an example of channels – increase the rate of water travel
- Also called carrier proteins
- Very specific for the molecules that they transport
- Transporters can reverse direction if the concentration gradient flips
- Glucose transporter is an example
- Concentration gradient is important for movement of molecules, but voltage difference between the two sides of the membrane can also play a role
Electrochemical gradient
Combined force due to the membrane voltage and concentration gradient
Electrochemical gradient when molecules are non-charged
- Movement based on concentration gradient ONLY, voltage difference plays no role
Electrochemical gradient when molecules are charged and voltage and concentration gradient work together
- Larger electrochemical gradient when voltage and concentration gradient work in the same direction
Electrochemical gradient when molecules are charged and voltage and concentration gradient oppose one another
- Smaller electrochemical gradient when voltage and concentration work in opposite directions