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Test: MCAT Biology
Hypersensitivity reactions occur when body tissues are affected by an abnormal immune reaction. The result is damage to normal tissues and clinical illness. A peanut allergy is an example of a hypersensitivity reaction, but there are three additional broad classes.
One class involves the abnormal production or deposition of antibodies. Antibodies are B-cell derived molecules that normally adhere to pathogens, rendering them unable to continue an infection. When antibodies are produced against normal tissues, however, disease can result. Figure 1 depicts a schematic structure of an antibody.
Antibodies can be divided into two peptide chains: heavy and light. Heavy chains form the backbone of the antibody, and are attached to light chains via covalent bonding. Each heavy and light chain is then further divided into constant and variable regions. Variable regions exhibit molecular variety, generating a unique chemical identity for each antibody. These unique patterns help guarantee that the body can produce antibodies to recognize many possible molecular patterns on invading pathogens.
1. | Humans must generate an enormous array of antibodies to account for all the possible patterns that they must recognize on pathogens. In fact, the diversity needed in antibody chains cannot be explained by DNA sequence variation. As a result, segments of DNA are physically rearranged in a process called VDJ rearrangement in order to create unique antibody chains. In order to carry out this process, DNA bonds must be broken. What kinds of intra-strand DNA bonds are most likely broken in this process? |
Base stacking interactions
Phosphodiester covalent bonds
van der Waals interactions
Peptide bonds
Hydrogen bonds
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