Final answer:
Protein carrier-mediated transport shows specificity, competition, and saturation, as each carrier protein targets specific molecules, competes for limited transport spots, and reaches a maximum rate when saturated.
Step-by-step explanation:
Protein carrier-mediated transport of molecules displays specificity, competition, and saturation. Carrier proteins in cell membranes are specialized to facilitate the movement of substances into and out of the cell. Each carrier protein is unique and specific for a single solute or a closely related family of solutes. This specificity ensures that the transport is selective, only permitting the passage of certain molecules while excluding others.
Competition occurs because there are a finite number of carrier proteins within the membrane. When multiple molecules are present that can bind to the same carrier protein, they will compete for transport spots, potentially limiting the rate at which each molecule can be transported.
Saturation happens when all carrier proteins are occupied by their ligands, reaching a maximum transport rate. At this point, any increase in the concentration gradient will not result in an increase in the rate of transport, as there are no more available carrier proteins to facilitate the transfer of additional molecules.
In summary, protein carrier-mediated transport shows all three characteristics: specificity, competition, and saturation, embodying the complexity of cellular transport mechanisms.