Which is True About Mediated Transport of Substances Across Cell

Question

Which is true about mediated transport of substances across cell membranes?
A)It involves a specific membrane protein that functions as a carrier molecule.
B)It always involves the movement of substances against a concentration gradient.
C)It is always directly coupled to the splitting of ATP molecules.
D)There is no limit to how fast it can occur as the concentration gradient becomes larger.
E)It is the main mechanism for transporting hydrophobic molecules across membranes.

Accepted Answer

Mediated transport involves a specific membrane protein that functions as a carrier molecule, facilitating the movement of substances across the membrane. These carrier proteins may have specific binding sites for the substances they transport and undergo conformational changes to transport the substance across the membrane.

Option B is incorrect as mediated transport can occur both with and against a concentration gradient.

Option C is incorrect as mediated transport may or may not require the splitting of ATP molecules, depending on the specific carrier protein and the substances being transported.

Option D is incorrect as there is a limit to how fast mediated transport can occur, depending on the number of available carrier proteins, their affinity for the substance being transported, and the concentration gradient of the substance.

Option E is incorrect as hydrophobic molecules may also be transported through other mechanisms such as simple diffusion or facilitated diffusion. Mediated transport can also transport hydrophilic molecules.