🧬AP Biology
6. Aquaporins are integral membrane proteins that facilitate the rapid transport of water molecules across cell membranes. The structure of the aquaporin channel is maintained by interactions between amino acid R-groups. A specific arginine residue (Arg-195) within the channel is thought to be critical for water passage.
Scientists created yeast strains expressing either wild-type (WT) aquaporin or one of two mutant forms. In the aqp-L mutant, the arginine at position 195 is replaced by leucine. In the aqp-P mutant, a different residue in a transmembrane helix is replaced by proline. A strain lacking the aquaporin gene (null) was used as a negative control. The scientists measured the rate of water transport into the cells (Figure 1A) and the relative amount of aquaporin protein localized to the plasma membrane (Figure 1B).
Figure 1. Bar graphs showing (A) relative rate of water transport into yeast cells and (B) relative abundance of aquaporin protein localized to the plasma membrane for four strains: WT, aqp-L (Arg195Leu), aqp-P (Pro substitution in a transmembrane helix), and null (no aquaporin gene).
Based on Figure 1A, identify the mutant strain that exhibits a relative water transport rate of approximately 0.2.
Based on Figure 1B, describe the difference in aquaporin protein abundance between the aqp-L strain and the aqp-P strain.
Scientists hypothesize that the mutation in the aqp-L strain disrupts the function of the water-conducting pore without affecting the stability of the protein. Use the data in Figures 1A and 1B to support the scientists' hypothesis.
Based on the chemical properties of amino acid R-groups, explain why the replacement of arginine with leucine in the aqp-L mutant results in the phenotype observed in Figure 1A.
