A cell membrane is built to encase the internal environment of the cell from its external environment. Not only does the membrane protect the cell by acting as a barricade it also selectively transports molecules into and out of the cell. The exchange, secretion or absorption of molecules helps maintain a healthy environment within a cell. A selective membrane allows the transport of molecules at an optimum rate for a cell/organism to survive. To truly understand how biological membranes can selectively transport molecules you need to understand the structure of the membrane.
The Biological membrane
Biological membranes are often described as selective regarding the transport of molecules, to understand the mechanisms of transport and selectivity …show more content…
Water is one of the few polar molecules to penetrate the phospholipid bilayer, the fact that the phospholipid bilayer contains a hydrophobic interior this is remarkable. Water tends to move from higher water potential (high concentration of water) to a low water potential (low concentration of water). Water potential is affected by solutes within the water that increases the entropy of water. As the solutes cannot diffuse across the membrane unassisted, water molecules do. Water again moves towards equilibrium, moving across the membrane to an area of high solute concentration using the minimum amount of free energy, increasing the water …show more content…
Active transport establishes different environments on each side of the membrane unlike diffusion. Active transport moves away from a thermodynamic equilibrium by moving molecules up and concentration gradient or against an electrochemical gradient. In order to move molecules in an unfavourable direction energy is required to “pump” molecules and often from ATP. Therefore proteins involved in active transport must also have mechanisms to harvest energy like ATP binding sites within the protein as well as mechanisms for transporting of molecules. Active transport has three purposes: for the absorption of nutrients from the external environment across the membrane into the cell; secretion of waste products out of the cell despite high concentrations of said product in the external environment; and to maintain non-equilibrium concentrations of ions like in nerve
The Biological membrane
Biological membranes are often described as selective regarding the transport of molecules, to understand the mechanisms of transport and selectivity …show more content…
Water is one of the few polar molecules to penetrate the phospholipid bilayer, the fact that the phospholipid bilayer contains a hydrophobic interior this is remarkable. Water tends to move from higher water potential (high concentration of water) to a low water potential (low concentration of water). Water potential is affected by solutes within the water that increases the entropy of water. As the solutes cannot diffuse across the membrane unassisted, water molecules do. Water again moves towards equilibrium, moving across the membrane to an area of high solute concentration using the minimum amount of free energy, increasing the water …show more content…
Active transport establishes different environments on each side of the membrane unlike diffusion. Active transport moves away from a thermodynamic equilibrium by moving molecules up and concentration gradient or against an electrochemical gradient. In order to move molecules in an unfavourable direction energy is required to “pump” molecules and often from ATP. Therefore proteins involved in active transport must also have mechanisms to harvest energy like ATP binding sites within the protein as well as mechanisms for transporting of molecules. Active transport has three purposes: for the absorption of nutrients from the external environment across the membrane into the cell; secretion of waste products out of the cell despite high concentrations of said product in the external environment; and to maintain non-equilibrium concentrations of ions like in nerve