Molecular biology: Protein transport mechanisms

Question

What are the three main intracellular transport mechanisms for proteins? How does cell topology influence the particular mechanisms needed to transport a protein among organelles intracellularly?

Answer 1

Hi Rx V.

There is active and passive transport using carrier proteins and carrier proteins can further be divided into three categories based on the directionality of the transported molecule or ions:

1. Uniport- transport of one solute at a time, in one direction (the root uni means "one")
2. Symport- transports two solutes at the same time in the same direction (the root sym means "agreement" or "together")
3. Antiport- transports two solutes at the same time in opposite directions (the root anti means "opposed to; against")

Cell topology influences the particular mechanisms needed to transport a protein among organelles intracellularly because of polarity (hydrophobic/hydrophilic), particularly the hydrophobic exteriors of cell membranes and hydrophilic interiors. This is the reason transmembrane proteins are often necessary for the transport of large or charged atoms or molecules.

Atomic/molecular gradients also influence passive transport such as diffusion and facilitated diffusion, with molecules flowing from high to low concentrations.