The resulting distorted shape of the cell serves as a

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The resulting distorted shape of the cell serves as a signal to the spleen to remove the damaged cells from circulation, leading to the severe anemia. Although this question was framed in an ancient context, the problem is ongoing. For centuries, schoolteachers on the Mediterranean island of Sar- dinia have witnessed a curious phenomenon. Every February as Spring arrives, some of their students (mostly boys—the G6PD gene is on the X chromosome) suddenly seem drained of energy. For the next three months, their schoolwork suffers, and they complain of dizziness and nausea and fall asleep at their desks. Then, just as suddenly, they return to normal and remain healthy and active until the next February rolls around. In children it might be brushed off as ‘spring fever,’ but Sardinian adults (mostly males) suffer the same symptoms. It was during the Korean War that the connection was made between the Mediterranean form of G6PD deficiency and the hemolytic effects of anti- malarial drugs, which, like the substance in fava beans, are oxidizing agents. The collapse of some soldiers, who were given such prophylactic drugs, led to a detailed investigation of the problem. 10–61 Transmembrane domains that are composed entirely of hydrophobic amino acid side chains obviously cannot interact with one another via hydrogen bonds or electrostatic attractions, two of the more important ways to link proteins together noncovalently. Nevertheless, they can interact specifically via van der Waals attractions. If their surfaces were complementary, they could fit together well enough to make a large number of van der Waals con- tacts, which would hold them together. It should be noted that the trans- membrane segment of glycophorin contains a few polar amino acids that may participate in the dimerization process. 10–62 Proteins can be restricted to specific regions of the plasma membrane in several ways: by attachment to extracellular or intracellular proteins, by attachment to proteins in other cells, and by molecular fences that in some way corral proteins in specific membrane domains. The fluidity of the lipid bilayer is not significantly affected by the anchoring of membrane proteins; the lipid molecules flow around anchored proteins like water around rocks in a stream. A230 Chapter 10: Membrane Structure
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10–63 Most of the carbohydrate in the carbohydrate layer is attached to intrinsic plasma membrane molecules. The carbohydrate layer typically contains gly- coproteins and proteoglycans that have been secreted into the extracellular space and then adsorbed on the cell surface. Many of the adsorbed macro- molecules are components of the extracellular matrix. So, are these bridging molecules part of the plasma membrane, or part of the extracellular matrix? This is the ambiguity that makes ‘where the plasma membrane ends and the extracellular matrix begins’ largely a matter of semantics.
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