Aquaporin-1 exists in the cell membrane as a tetramer. Each monomer is a water channel that can hold 4 molecules of water at a time. How many water molecules would be present in a complete aquaporin complex in the membrane of a red blood cell at one time?

16

Explanation:

Aquaporin 1 is a protein coding which exists as a tetramer {a tetramer is an oligomer formed from four monomers}. It functions as a molecular water channel proteins and also a non-selective cation channels. Each monomer in a complete aquaporin complex can form four (4) water molecules. As such, there will be sixteen (16) molecules of water present in an Aquaporin-1 Complex.