A protein, is a protein that changes conformation as each ion or molecule crosses the membrane it is embedded in. This is in contrast to a channel, which lets molecules through without changing conformation for each molecule or ion. Channels can change conformation to open, close or inactivate, but they do not change conformation with each molecule that crosses.

The correct answer is: carrier.

Explanation:

Carrier proteins are a type of integral proteins (meaning they're embedded in the membrane) that facilitate the transport of ions, charged particles, and polar molecules.

Carrier proteins undergo conformational changes when ions or polar molecules bind to them, which makes them rearrange in a way these particles and molecules can cross through the membrane.

during the process of dna replication, brdu can replace thymidine and incorporate into the newly synthesized dna, cell proliferation thus can be reflected in the extent of brdu incorporation.

enzyme active site and substrate specificity

enzymes bind with chemical reactants called substrates. there may be one or more substrates for each type of enzyme, depending on the particular chemical reaction. in some reactions, a single-reactant substrate is broken down into multiple products