lab
...postulated that membranes are made of lipids (1). Later the membranes were analyzed and found to contain lipids and proteins, the most abundant of them being the phospholipids. They are amphipathic molecules that have both hydrophilic and hydrophobic regions. Thus the membrane exists as a phospholipid bilayer with proteins and carbohydrates suspended in it. The proteins are free to move randomly across the plane of the membrane and determine the unique structure of the membrane. The membrane has fluidity and is not static, where weak hydrophobic interactions hold the membrane together. Hence the term fluid mosaic model. The membrane is affected by changes in temperatures. Lower temperatures result in hardening of the membrane unless there are unsaturated hydrocarbon tails that develop kinks and prevents the close packing of the molecules, thus preventing solidifying. In addition to temperature, cholesterol also affects the fluidity of the membrane. Cholesterol reduces membrane fluidity as well as prevents solidification of the membrane. Thus the membrane is a matrix of lipid bilayers with integral and peripheral proteins. These proteins combine to give a strong framework to the cell. The biological membrane regulates transport and thus enables the cell to function normally. For example the muscle cells exchange sugars, amino acids and nutrient for waste products produced during metabolism. The movement of substances occurs at different rates; ions and polar molecules cannot easily traverse the membrane while hydrophobic molecules such as carbon dioxide and oxygen and polar uncharged molecules like water and ethanol can pass through rapidly (1). For example, transporter proteins help glucose diffuse across retinal pigment epithelium (2) but some molds are limited to using simple diffusion for glucose uptake (3). The purpose of our laboratory experiment is to study the movement of molecules by diffusion across dialysis tubing, which is also semi-permeable, and thus better understand the working of cell membranes. Diffusion is the passive movement of substances due to thermal motion of molecules...