CARRIER MEDIATED VS WITHOUT CARRIER TRANSPORT

CARRIER MEDIATED VS WITHOUT CARRIER TRANSPORT

• Division of transport mechanisms based on carrier protein involvement.

1. Transport without carrier:

• No Carrier protein involved.
• E.g., simple diffusion, osmosis.

2. Carrier-mediated transport:

• Carrier protein involved.
• Mainly in transport of solutes.
• All carrier-mediated transport shows saturation.

Transport methods included:

• Facilitated diffusion – 
  • Along concentration gradient (”downhill movement” & no energy required).
• Active transport – 
  • Against concentration gradient (“uphill movement” & energy required).

Subtypes:

1. Uniport:

• Carrier protein transports only one type of molecule.

2. Co-transport/Symport:

• Transport of one substance by carrier protein linked to transporting another substance.
• Both transported in same direction.

Eg:

• Glucose & amino acids – Transported along with Na+.
• An example of secondary active transport (combination of facilitated diffusion & active transport).

3. Counter-transport/antiport:

• Transport protein exchanges one substance for another (two substances transported in opposite direction by carrier protein).

Eg:

• Sodium-calcium counter-transport.
• Sodium-hydrogen counter-transport in proximal tubules.

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