Immunoassay

Immunoassay techniques are used for nanogram level determination of hormones, drugs and vitamins. This method involves formation of a complex precipitate as a result of reaction of antigen and antibody. For measuring small amounts of insulin, this was first employed and the method was known as radioimmunoassay. The complex precipitate that formed as a result of antigen-antibody reaction is known as antigen-antibody complex. The intrinsic association constant between an antibody and a univalent antigen is known as affinity. The total binding energy between antibodies and a multivalent antigen is known as avidity. The three parameters which influence the specificity of immunoassays are heterogeneity of the antibody, cross reaction with other antigens and possible interferences of the antigen-antibody reaction from low-molecular weight substances which is altering the environment of the reaction. Use of monoclonal antibodies enhances the specificity. Two popular immunoassay techniques are enzyme-linked immunosorbent assays and fluorescence immunoassays.

Biological functions of proteins

Proteins play an important role in the functions of human body. Proteins are naturally occurring polypeptides of molecular weight greater than 5000. These large molecules perform a wide range of biological functions. Enzymes which are proteins are capable of boosting rates of reactions up to 10¹² times.  Some carrier proteins are capable of transporting tiny molecules and ions in the blood and within cells. Hemoglobin and ferritin are examples of such proteins. Some proteins impart tensile strength to skin, bone and teeth. Such proteins are called mechanical proteins and collagen is an example. Actin and myosin are two proteins which help in muscle contraction in human body. Myosin is also capable of converting chemical energy to mechanical energy. The antibodies which protect human body by destructing foreign cells are proteins. Rhodopsin is a visual protein which is located in membranes of retinal cells is capable of transferring signals to the interior of the cell.