Only answer \'C\' please. The more detail the better. Thank you! Aquaporins are
ID: 166500 • Letter: O
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Only answer 'C' please. The more detail the better. Thank you!
Aquaporins are protein channels embedded in the plasma membrane of certain organisms. As their name suggests, these channels move water through the membrane at a very high rate. Several features of aquaporin channels are dependent upon specific amino acids at various points in the channel and are important for the function of the protein. Aquaporins are selective for water but not hydronium ions. Proton movement through the channel would allow depolarization of the membrane and imminent death of the cell or organism. Near the top of the channel, certain conserved amino acids work to attract the polar water molecule but strongly repel hydronium ions. Which amino acids might these be? Why is moving hydronium through a water channel so undesirable? Aquaporins at their narrowest point in the channel itself is 2.8A, which happens to be the approximate size of a water molecule. A histidine projects into the channel at this point forming the size gate of the aquaporin. Propose what you think might happen to the function of the channel if histidine were replaced with lysine, phenylalanine or alanine. Aquaporins have a region near the center of the pore called a water dipole reorientation. The conserved asparagine's are present at this point and each forms a hydrogen bond from its amino hydrogen to the oxygen on a single water molecule. In this way, all the H-bonding donor potential of a single water molecule is satisfied by the protein. What does this mean about hydrogen bonding from this single water molecule with neighboring water molecules in the channel? Why is this important? What part of asparagine H-bonds with water? Note that a chain of water molecules H-bonded to one another allows for "proton hopping" through the channel, which would effectively move hydronium. Propose what would happen to the function of the protein if the asparagines in the water dipole reorientation were mutated to glutamine or to aspartate. In order for water molecules to pass through the channel, they must "slide" at some points. We have already discussed the various points in the channel that contain amino acids that interact with and attract water molecules to the protein channel. However, for continued movement through the channel, there must be regions that are slick and effectively repel water toward the next sticky spot in the channel. Which amino acids might be present in the slick spots?Explanation / Answer
1. Two signature NPA motifs are juxtapose by van der Waals associated each other.
2. The dipoles caused by two short alfa-helices results positive change surrounding conserved asparagine.
3. Water molecule form partial hydrogen bonds with both the hydrogen. Thus undergoing a temporary dipole reorientation of the water molecule.
4. After further water molecule interacts with sting of carbonyl oxygen on the peptide backbone and exit the channel.
5. The orientation of oxygen changes in such a way that it faces down so that forming hydrogen bonds to the water oxygen, there by putatively impeding the hopping of a proton to and from the water molecule enters from the extracellular side.
6. As the narrow aquaporin channel the entry of molecules is controlled by size restriction and electrostatic repulsion.
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