BIBC 100 Midterm Exam 1. (24) Draw a diagram of the quaternary structure of immunoglobulin IgG including disulfide bridges and antigen recognition site. (8 pts) a. Define a disulfide bridge. (4 pts) Covalent bond between Sulfur atoms on two different Cys residues of a polypeptide chain or between chains, stabilizes protein structure when under oxidizing conditions b. How many subunits make up an active molecule and what is the motif of the protein fold? (6 pts) 2 LC + 2 HC = heterotetramer fold is distorted β-barrel c. The antigen is recognized by what part of the IgG; which part of that motif specifically? (4 pts) Variable region of LC and HC recognition at the loops of the β-barrel d. What is the smallest unit of an antibody molecule that can retain the specificity of the whole molecule? (2 pts) Fab fragment
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