| Back | Selectively PermeableA. The cell “selects” what materials enter or exit the cell through the membrane.II. Membrane StructureA. Phospholipids make up the majority of the cell membrane and also organelle membranes.1. These are Amphipathic Molecule. (It means there is a hydrophilic and hydrophobic component.)2. These molecules create the bi-layer and the structure is held intact by the presence of water outside andinside the cell. The negatively charged phosphorus line up to make a barrier preventing water fromforming hydration shells, water surrounding a molecule, around the phospholipids and therebydissolving the membrane.B. Proteins1. These are also Amphipathic molecules. (This is due to proteins folding into a 3-D structure and thatproteins are composed of amino acids, of which some are polar and some are non-polar.)2. Two types of proteins are present on membranes:a. Integral – These run completely through the bi-layer from the outside to the inside.i. These function in the transport of molecules and foundation. (Help to maintain theINTEGRITY of the structure.)b. Peripheral – These are located on one side of the membrane. (They do not extend into the bi-layerof the membrane.i.These act as sites for attachment of the Cytoskeleton on the inside of the cell and theattachment of the Extra Cellular Matrix, ECM, (like armor for the fragile cell) on the outsideof the cell.3. The proteins of the cell membrane can have several functions.a. Molecule transport (Helps move food, water, or something across the membrane.)b. Act as enzymes (To control metabolic processes.)c. Cell to cell communication and recognition (So that cells can work together in tissues.)d. Signal Receptors (To catch hormones or other molecules circulating in the blood.)e. Intercellular junctions (For “stiching” cells together to make tissues.)f. Attachment points for the cytoskeleton and ECMC. Cholesterol1. This molecule helps keeps the cell membrane flexible to some degree.2. It also helps to keep the cell membrane of plant cells from freezing solid in very cold temperatures, likethe Tundra.D. The membrane is described as a Fluid-Mosaic model because it looks like a moving (Fluid) puzzle (mosaic).All the pieces can move laterally, like students moving from seat to seat. The proteins moving in this sea ofphospholipids would be like the teacher moving around the student desks. Imagine the ceiling and floor are watermolecules. They keep you from moving up and down to some extent by their presence.1. Scientific Modela. These are used to represent what is difficult to actually see. (Like a model of the solar system. orthe model of DNA or a cell membrane. |