Correct option is B
The correct answer is option (b): Aquaporins are not absent in bacteria. This statement is incorrect, as aquaporins are found in bacteria, plants, and animals. In fact, the first aquaporin was discovered in Escherichia coli (a bacterium), where it was known as AqY (Aquaporin Y). These proteins form water channels and are essential for regulating water transport across cell membranes in all domains of life.
Let’s break down why the other options are correct:
Option (a): Aquaporins are indeed integral membrane proteins that belong to the Major Intrinsic Protein (MIP) family. This family also includes other transport proteins such as glycerol channels. Aquaporins specifically facilitate the rapid transport of water molecules across the membrane.
Option (c): A highly conserved Asn-Pro-Ala (NPA) triad is a well-known structural feature of aquaporins. The NPA motif plays a critical role in the selective permeability of aquaporins to water molecules, ensuring that only water can pass through while excluding other small molecules.
Option (d): The Asn-Pro-Ala (NPA) triad is present in both the N-terminal and C-terminal halves of the aquaporin protein. This motif is crucial for maintaining the channel structure and functionality of aquaporins. Its position in both halves of the protein ensures the proper alignment and functioning of the water channel.
Thus, option (b) is the correct answer because aquaporins are indeed present in bacteria, and not absent as the statement suggests.
Information Booster:
Aquaporins and the MIP family: Aquaporins belong to the Major Intrinsic Protein (MIP) family of membrane proteins, which also includes other water- and solute-transporting proteins. These proteins are characterized by their structure, which typically includes six transmembrane helices and a highly conserved NPA motif that helps form the channel for water molecules.
Presence in Bacteria: Aquaporins were first identified in bacteria, where they are known as AqY in E. coli. These bacterial aquaporins share the same structural features as the aquaporins found in plants and animals. The presence of aquaporins in all three domains of life (bacteria, plants, and animals) emphasizes their evolutionary importance in water transport across cell membranes.
The NPA Motif: The Asn-Pro-Ala (NPA) triad is conserved across all aquaporins. It plays a key role in forming the selective permeability barrier for water molecules. The NPA triads are critical for the function of the protein, ensuring that the channel allows only water molecules to pass while excluding ions and other small molecules.
