Question

multiple choice question
a carrier protein that transports solute molecules by facilitated diffusion has ____ configuration(s) because ____.

• two; it needs to bind solute outside the cell and then release it in the cytoplasm
• one; each solute binds to only one carrier protein
• one; the protein has a single active site for binding solute
• multiple; each solute has a different binding site

Explanation:

To solve this, we analyze each option:

• Option 1: Carrier proteins in facilitated diffusion (like those for glucose) have two conformations (e.g., open to extracellular space, then open to cytoplasm) to bind solute outside and release inside. This matches how facilitated diffusion carriers work.
• Option 2: Solutes can bind to specific carriers, but this doesn't explain configuration count. Incorrect.
• Option 3: Carrier proteins change conformation (so more than one), so "one" is wrong. Incorrect.
• Option 4: Facilitated diffusion carriers for a solute have a specific binding site, not multiple per solute. Incorrect.

Answer:

A. two; it needs to bind solute outside the cell and then release it in the cytoplasm