BPK 105 Final: Module 9 - Review Questions - Part 5
27 Apr 2018
School
Department
Course
Professor
Module 9 - Review Questions - Part 5
7. Describe the structure and function of antibodies. Describe the different effects
antibodies have in immunity. [6 marks]
Structure of Antibodies
- Antibodies are proteins produced in response to an antigen.
- They are Y-shaped molecules consisting of four polypeptide chains: two identical heavy
chains and two identical light chains (figure 14.12).
- The end of each “arm” of the antibody is the variable region, the part of the antibody that
combines with the antigen. The variable region of a particular antibody can join only with
a particular antigen; this is similar to the lock-and-key model of enzymes (see chapter 2).
- The rest of the antibody is the constant region, and it has several functions. For
example, the constant region can activate complement, or it can attach the antibody to
cells, such as macrophages, basophils, and mast cells.
- Antibodies make up a large portion of the proteins in plasma. Most plasma proteins can
be separated into albumin and alpha, beta, and gamma globulin portions (see chapter
11). Antibodies are sometimes called gamma globulins, because they are found mostly
in the gamma globulin part of plasma, or immunoglobulins (Ig), because they are
globulin proteins involved in immunity. The five general classes of antibodies are
denoted IgG, IgM, IgA, IgE, and IgD (table 14.2).
Effects of Antibodies
- can affect antigens either directly or indirectly.
- Direct effects occur when a single antibody binds to an antigen and inactivates the
antigen, or when many antigens are bound together and are inactivated by many
antibodies (figure 14.13a,b
).
- The ability of antibodies to join antigens together is the basis for many clinical tests, such
as blood typing, because when enough antigens are bound together, they form visible
clumps.
- Most of the effectiveness of antibodies results from indirect effects (figure 14.13c
–e
).
After an antibody has attached by its variable region to an antigen, the constant region of
the antibody can activate other mechanisms that destroy the antigen.
- For example, the constant region of antibodies can activate complement, which
stimulates inflammation, attracts white blood cells through chemotaxis, and lyses
bacteria.
- When an antigen combines with the antibody, the constant region triggers the release of
inflammatory chemicals from mast cells and basophils.
- For example, people who have hay fever inhale the antigens (usually plant pollens),
which are then absorbed through the respiratory mucous membrane. The combination of
the antigen with antibodies stimulates mast cells to release inflammatory chemicals,
Document Summary
Module 9 - review questions - part 5: describe the structure and function of antibodies. Describe the different effects antibodies have in immunity. Antibodies are proteins produced in response to an antigen. They are y-shaped molecules consisting of four polypeptide chains: two identical heavy chains and two identical light chains (figure 14. 12). The end of each arm of the antibody is the variable region, the part of the antibody that combines with the antigen. The variable region of a particular antibody can join only with a particular antigen; this is similar to the lock-and-key model of enzymes (see chapter 2). The rest of the antibody is the constant region, and it has several functions. For example, the constant region can activate complement, or it can attach the antibody to cells, such as macrophages, basophils, and mast cells. Antibodies make up a large portion of the proteins in plasma.
