Practice - Membrane Structure 2: Videos & Practice Problems

A hydropathy plot is a graphical representation used to predict membrane-spanning segments in a protein sequence. It plots the hydrophobicity of amino acids along the protein sequence. The plot has a zero point, with positive regions indicating hydrophobic (water-repelling) segments and negative regions indicating hydrophilic (water-attracting) segments. To predict membrane-spanning segments, you look for stretches of about 20 amino acids in the hydrophobic region, as these are likely to span the lipid bilayer. This method helps identify transmembrane domains essential for protein integration into the membrane.

Temperature significantly impacts the fluidity of a lipid bilayer. Increasing the temperature enhances fluidity because the lipid molecules gain kinetic energy, causing them to move more freely. Conversely, decreasing the temperature reduces fluidity as the lipid molecules lose kinetic energy and pack more tightly together. This temperature-dependent behavior is crucial for maintaining membrane integrity and function under varying environmental conditions.

Unsaturated fatty acids play a crucial role in increasing membrane fluidity. They contain one or more double bonds, which introduce kinks in the fatty acid chains. These kinks prevent the fatty acids from packing tightly together, lowering the melting point and increasing the fluidity of the membrane. This property is essential for maintaining membrane flexibility and function, especially in varying temperatures.

Peripheral membrane proteins are proteins that associate weakly with the membrane, typically through non-covalent interactions such as hydrophobic interactions, electrostatic forces, or hydrogen bonds. They do not penetrate deeply into the lipid bilayer and are usually found on the membrane's surface. These proteins can be released from the membrane using mild treatments like changes in pH or ionic strength, unlike integral membrane proteins that require detergents for removal. Peripheral membrane proteins often play roles in signaling, maintaining cell shape, and interacting with the cytoskeleton.

The length of alkyl chains in fatty acids significantly affects membrane fluidity. Longer alkyl chains increase the melting point of the fatty acids, leading to a more rigid and less fluid membrane. In contrast, shorter alkyl chains have lower melting points, resulting in a more fluid membrane. This relationship is crucial for maintaining the proper balance of membrane fluidity, which is essential for various cellular processes, including membrane protein function and cell signaling.