Question

Aquaporins are integral proteins of the plasma membrane whose role is to allow the passage of water molecules down its concentration

gradient. Recent observations have shown an interesting arrangement of charged amino acids residues along the inner surface of the
channel, resulting in the entry of water via its oxygen then flipping the lead with its hydrogens half way through the channel. How might
this explain aquaporin's specificity for water and not cations or protons?
A Cations such as K* and Na* would be repelled at the opening of the channel
B Water gains access because it is electrically neutral
Protons cannot cross since they do not interact with water
Water, a small polar molecule, is able to interact with both negative and positive residues in the channel

Answer 1

Answer:**D. Water, a small polar molecule, is able to interact with both negative and positive residues in the channel.**

Step-by-step explanation:

The specificity of aquaporins for water and not cations or protons can be explained by the arrangement of charged amino acid residues along the inner surface of the channel. The correct explanation is:

Here's why this explanation is accurate:

1. **Amino Acid Residues:** The arrangement of charged amino acid residues along the inner surface of the aquaporin channel creates a polar environment. Water is a polar molecule, which means it has a partial positive charge (hydrogen) and a partial negative charge (oxygen). These charged amino acid residues can interact with water molecules through hydrogen bonding, allowing water to pass through.

2. **Size and Charge:** Cations like K+ and Na+ are larger ions with a full positive charge. The arrangement of charges in the channel may not favor the passage of these larger, positively charged ions, which would be repelled or obstructed. Protons (H+ ions) are also smaller than cations but may not interact favorably with the charged residues in the same way that water does.

3. **Specificity for Water:** Water's ability to form hydrogen bonds with both negatively and positively charged residues in the aquaporin channel allows it to pass through the channel efficiently. The interaction between water and the charged residues ensures that water can move through the channel while excluding other ions and molecules that do not interact as effectively with the channel's charges.

So, the arrangement of charged amino acid residues in aquaporins creates a favorable environment for water molecules to pass through the channel, making aquaporins specific for water and not cations or protons.