Infectious Science Assignment

1. (a) Describe antibodies' molecular structure, classes, and function. (10 marks)

Antibodies, also called immunoglobulin, are defensive proteins produced to respond to foreign bodies. The structure and function of antibodies vary based on their composition, where some only consist of single molecules such as IgD, IgE, and IgG antibodies (Wang et al., 2018). Apart from monoclonal antibodies, other classes of antibodies include those with double molecules such as IgA and those with multiple clustered molecules such as the five molecule cluster antibody, IgM. These examples form the five classes of antibodies. However, these antibodies are similar in their single molecular structure and basic functions. A single antibody molecule has a general "Y" shape and comprises two major parts of its structure, each consisting of two polypeptides. This includes the heavy chain and the light chain segments of the molecule. The heavy chain consists of a constant region which further includes an Fc region. The constant region determines the class of the antibody and its function. The light chain area includes both a constant and variable region, in which the variable region contains an antigen-binding site that includes a hypervariable region responsible for creating an opening that surrounds the protruding antigen area. Therefore, some of the major functions of an antibody include agglutination, which involves joining antibodies with bacteria, forming large complexes that neutralize and remove the bacteria. Another function of antibodies includes phagocytosis. In this case, antibody molecules contain complementary proteins in the heavy region that activate phagocytes which are used to overwhelm antibody and antigen complexes to eliminate them (Wang et al., 2018). Antibodies are also used to attack the surfaces of antigens and their cells, which join with natural killer cells in the Fc region to release perforating enzymes that kill the antibody.