Antibody: Definition, Structures,Types and properties of different antibodies

Antibody: Definition, Structures, Types and Properties of Different Antibodies

Definition of antibody

The antibody is also called immunoglobulin (Ig). Immunoglobulin is a glycoprotein that is made in response to an antigen and can recognize and bind to the antigen that caused its production. It protects us from microbial infection. They are gamma globulin and synthesized by plasma cells. They constitute 25-30 % of total serum proteins. Antibodies are present in serum, tissue fluids, and mucosal surfaces and on the surface of B-cells where they act as antigen receptors.

Structure of immunoglobulin

Composed of 4 polypeptide chains- 2 identical light chains (25 kDa each) and 2 identical heavy chains (50-73 kDa each)
Linked by disulfide bonds
Light chains similar in all immunoglobulins
Light chains occur in 2 varieties:-kappa (k) and lambda( λ )
Kappa chains are more frequently found.
Heavy chains:- gamma, alpha, mu, delta and epsilon.
One Ig contains one type of light chain and one type of heavy chain.

Fc (Fragment Crystallizable ) -fixes complement
Fab( Fragment, antigen-binding) binds antigen.
Fab terminal has amino and Fc terminal have-COOH group.
L and H chain consists of 2 parts-

V (variable) region at amino terminal & C (constant) region at carboxyl terminal.

Hypervariable region: binds epitope also called complement determining region (CDR).
Look at the above structure of the antibody.

Types of antibody

Based on the structure and antigenic nature of heavy chains the immunoglobulins are classified into 5 classes.
Ig G- (gamma)
Ig A- (alpha)
Ig M- (mu)
Ig D- (delta)
Ig E – (epsilon)

Properties of antibodies

Properties of Antibodies

Keynote: All antibodies are immunoglobulins but not all immunoglobulins are antibodies e.g. cryoglobulin is immunoglobulin but not antibody.

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