Question

2. The function of channel proteins in membrane is to: A. Transport phospholipids across the membrane B. Act as receptor molecules which can bind to ligands C. Permit the diffusion of specific substances through the membrane D. Bind to a substance on one side and release it on the other side of the membrane​

Answer 1

A) The simplest mechanism by which molecules can cross the plasma membrane is passive diffusion. During passive diffusion, a molecule simply dissolves in the phospholipid bilayer, diffuses across it, and then dissolves in the aqueous solution at the other side of the membrane.

B) G-protein-linked receptors bind a ligand and activate a membrane protein called a G-protein, which then interacts with either an ion channel or an enzyme in the membrane. Enzyme-linked receptors are cell-surface receptors with intracellular domains that are associated with an enzyme.

C) Water moves across cell membranes by diffusion, in a process known as osmosis. Osmosis refers specifically to the movement of water across a semipermeable membrane, with the solvent (water, for example) moving from an area of low solute (dissolved material) concentration to an area of high solute concentration.

D) Carrier proteins bind specific molecules to be transported on one side of the membrane. They then undergo conformational changes that allow the molecule to pass through the membrane and be released on the other side.