What are Proteins and What do They Do?

"In many proteins, the polypeptide chain turns at a specific site and folds back and forth to generate a tertiary structure of the protein" (Sadava, 2011, p. 46). Finally, the protein also has a quaternary structure. "Quaternary structure of protein consists of subunits" (Sadava, 2011, p. 47). "The quaternary structure of proteins is derived from the way these subunits combine with each other to interact" (Sadava, 2011, p. 47). In this experiment, students analyze unknown proteins and their sizes and subunits.

Proteins can be informally classified into three broad categories associated with typical tertiary structures: globular proteins, fibrillar proteins, and membrane proteins. Almost all globular proteins are soluble and many of them are enzymes. Fibrin is usually structural, such as collagen, the main constituent of connective tissue, or the protein component of keratin, hair and nails. Membrane proteins usually function as receptors or become permeable through the cell membrane for polar or charged molecules.

The basement membrane has four major components. Laminin itself is a trimeric protein, the main organizer of the basement membrane, as it interacts with other components in the basement membrane and proteins in epithelial cells. Type IV collagen forms a network of felt fibers that imparts its tensile strength to the base film. Nidogen and Perlecan are two small proteins that bind the collagen network to laminin. Basement membranes have several other components, including fibronectin.

The first batch of protein to be purified is a water soluble protein. Purification of integral membrane proteins requires disruption of the cell membrane to separate any particular protein from other proteins within the same membrane compartment. For example, it may be possible to first isolate a specific membrane fraction, in order to isolate the mitochondria from the cells, prior to purification of the proteins located in the mitochondrial membrane. Surfactants such as sodium dodecyl sulfate (SDS) can be used to solubilize cell membranes and keep the membrane proteins in solution during purification; however, due to the denaturation of SDS, the use of Triton X - 100 A more mild surfactant can be used. Or CHAPS retains the natural conformation of the protein during complete purification

Introduction Detergents are used to extract membrane proteins from biofilms and to adjust their solubility in aqueous solutions. This is a prerequisite for further protein purification (1). Purification of membrane proteins is often awkward because they migrate from their natural membrane environment into detergent buffers that partially mimic the physical and chemical properties of the lipid membrane (2). Thus, many membrane proteins do not retain their biological activity after extraction, or retain their biological activity only partially or only under very specific buffering conditions. After extraction, purification of the membrane protein is usually accomplished by the same chromatography method as soluble protein, except that the surfactant must always be present in the buffer. Detergents do not interfere with ion exchange or metal chelate chromatography.