The article by Donald M. Engelman challenges the traditional "fluid mosaic" model of membrane structure, highlighting new data that reveal membranes are more patchy and less fluid than previously thought. Key points include: 1. **Patchiness in the Membrane Plane**: Membranes are not randomly distributed but exhibit regions of segregated structure and function. Proteins and lipids tend to group together, forming oligomeric complexes and specific lipid-lipid interactions. This patchiness affects protein function and membrane curvature. 2. **Membrane Thickness**: The thickness of a lipid bilayer is influenced by the hydrophobic and hydrophilic interactions between proteins and lipids. Proteins can distort the bilayer to fit their hydrophobic regions, leading to variable bilayer thickness and curvature. 3. **Area Occupancy by Protein and Lipid**: The amount of membrane area occupied by proteins is variable, with some proteins covering large regions of the lipid bilayer. Protein lateral mobility is restricted by various factors such as crowding, ectodomain collisions, and transbilayer interactions. 4. **Consequences for Current Concepts**: The modified view of membranes suggests a more complex and variable structure, with regions of protein assemblies and lipid separation. This challenges the existing body of work on pure lipid systems and highlights the need for better understanding of protein-lipid interactions. The article emphasizes the importance of these new findings in shaping a more accurate and detailed understanding of membrane biology, which has been neglected due to technical challenges but is now gaining significant attention.The article by Donald M. Engelman challenges the traditional "fluid mosaic" model of membrane structure, highlighting new data that reveal membranes are more patchy and less fluid than previously thought. Key points include: 1. **Patchiness in the Membrane Plane**: Membranes are not randomly distributed but exhibit regions of segregated structure and function. Proteins and lipids tend to group together, forming oligomeric complexes and specific lipid-lipid interactions. This patchiness affects protein function and membrane curvature. 2. **Membrane Thickness**: The thickness of a lipid bilayer is influenced by the hydrophobic and hydrophilic interactions between proteins and lipids. Proteins can distort the bilayer to fit their hydrophobic regions, leading to variable bilayer thickness and curvature. 3. **Area Occupancy by Protein and Lipid**: The amount of membrane area occupied by proteins is variable, with some proteins covering large regions of the lipid bilayer. Protein lateral mobility is restricted by various factors such as crowding, ectodomain collisions, and transbilayer interactions. 4. **Consequences for Current Concepts**: The modified view of membranes suggests a more complex and variable structure, with regions of protein assemblies and lipid separation. This challenges the existing body of work on pure lipid systems and highlights the need for better understanding of protein-lipid interactions. The article emphasizes the importance of these new findings in shaping a more accurate and detailed understanding of membrane biology, which has been neglected due to technical challenges but is now gaining significant attention.