Membranes

• Biological membranes are mainly comprised of phospholipids which form a fluid bilayer
• The fluidity of a membrane is moderated by the balance of saturated vs unsaturated fatty acids and the inclusion of cholesterol
• Membranes contain 2 types of proteins: integral and peripheral
• Integral proteins are embedded in the bilayer and span the membrane
• Peripheral proteins are associated with the face of the membrane
• The fluid mosaic model is a model of the cell membrane that describes the membrane fluidity and the distribution of lipids and proteins
• There are 3 mechanisms for transport: passive diffusion, facilitated diffusion, and active transport
• Passive diffusion doesn't require aid of proteins or energy. The substance diffuses down its concentration gradient
• Facilitated diffusion requires the aid of transport proteins including channel and carrier proteins. These speed up the crossing of a specific solute
• Active transport requires ATP as an energy source for protein pumps. It often involves bulk transport, either exocytosis or endocytosis
• Exocytosis is when the solute exits the cell by transport vesicles fusing to the membrane and releasing
• Endocytosis involves the solute entering the cell by the membrane engulfing and digesting it
• Membranes have a hydrophobic interior and hydrophilic exterior