Cell Membrane Permeability

CELL MEMBRANE PERMEABILITY Cell membrane permeability is the ability of the cell membrane to transport substances the cell needs from the extracellular environment to the inside of the cell (cytosol). Vice versa, it also transports materials that will be released by the cell which originate from metabolic results from the stosol to the outside of the cell. The existence of the cell membrane creates a barrier for the process of entry and exit of metabolic materials from two directions. Sugars, amino acids, mineral salts and other nutrients enter the cells while metabolic waste products are excreted from the cells. Even though the traffic through the cell membrane is very dense, not all substances can pass through it haphazardly. Cells with selectively permeable cell membranes are able to take in a variety of small molecules and ions and reject others. The condition of the ability of cell membranes to be semi-permeable to certain molecules Gases, including O2 and CO2, small molecules, molecules without charge, urea and ethanol, can easily move from outside to inside the cell across the cell membrane by passive diffusion. Many molecules can move across membranes without involving transport proteins and without requiring energy. Many types of molecules and no ions can pass through the membrane by passive diffusion. Transport of these molecules both in and out requires a type of membrane protein to help. This also applies to the transport of molecules that require acceleration to enter the cell (such as water and urea), but still require special proteins because transport by passive diffusion is not sufficient for the cell's needs. Cell membranes have high permeability to water but low to salts and small molecules including sugars and amino acids. But ethanol is more permeable than water, because it has watermiseable properties that dissolve in water but can interact with fat. Polar molecules or liquids tend not to be able to enter cells because of the presence of fat in the cell membrane which, apart from being insoluble in water, also has non-polar properties. An example of polar and non-polar phenomena is oil mixed with water. The condition of non-polar oil will not be able to combine with water which is polar so it will form a layer that does not merge between the two. During osmosis, water will pass through a semipermeable membrane from a low solution concentration condition with lots of water to an area with high solution conditions with less water so that the water concentration on both sides becomes balanced. Water conditions in the cellular environment will cause cells to be in an isotonic, hypertonic or hypotonic condition. During osmosis, water will move through a semipermeable membrane from a high water concentration condition to an environment with a low water concentration condition until the overall concentration of the solution on both sides has the same amount of water. When the cells are in a place with isotonic environmental conditions (the total concentration of the solution in the animal's environment is the same as the fluid conditions in the cells), then there will be no movement of water from inside or outside the cells. In other conditions, when the cell is in a hypotonic condition (where the solution in the environment has a lower concentration than the fluid in the cell), water will tend to flow into the cell, causing the cell to expand and become larger. In contrast to this condition, when cells are in a hypertonic environment (where the solution in the environment has a higher concentration than the liquid in the cell), water will tend to flow out of the cell, causing the cell to shrink and wrinkle. Under normal body conditions, plasma membrane ion channels control the movement of ions from inside and outside the cell so that they are not involved in the movement of water and usually the cell volume will be balanced.