According to the fluid mosaic model, membranes are held together by hydrophobic interactions.
Considering the forces that some cells may experience, why do membranes not break apart every time an animal moves? (Figure 5.5)
Answer: As the name suggests for the fluid mosaic model, cell membranes have some degree of fluidity. The degree of fluidity varies with the composition of the membrane, but in all membranes, phospholipids are able to move about within the membrane. Also, due to the hydrophobic and hydrophilic opposite ends of phospholipid molecules, phospholipid bilayers form spontaneously. Therefore, if stressing forces happen to damage a membrane, adjacent phospholipids automatically move to fill in the opening.
Based only on amino acid sequence, how would you recognize an integral membrane protein?
(Figure 5.8)
Answer: Integral membrane proteins are those that are embedded within the membrane structure and provide passageways across the membrane. Because integral membrane proteins must pass through both polar and nonpolar regions of the phospholipid bilayer, the protein portion held within the nonpolar fatty acid interior of the membrane must also be nonpolar. The amino acid sequence of an intregral protein would have polar amino acids at both ends, with nonpolar amino acids comprising the middle portion of the protein.