Question

Decsribe the molecular structure of an antibody and describe th different classes of antibodies

Answer 1

Antibodies

Part of heterogenous group called gammaglobulins

Found in serum

Immunoglobulins is a general term (IgG, IgA, IgM, IgD, IgE)

Antibodies more specific term used to describe an immunoglobulin= antigen specificity (Anti-HBsAg)

Are bivalent= one antibody molecule will bind to two antigen molecules (has 2 arms)

Structure of Antibody

Has 4 chains. 2 heavy and 2 light chains

Disulfide bond linkage between the chains

Each chain has a constant region

Each chain has variable region--Specificity available, antigen binding region

IgG

Highest concentration in humans 75-80%

Only isotype that can cross the placenta

Responsible for protecting infant in first weeks of life

4 subclasses= IgG 1-4

Most common subclass is IgG1

IgM

First antibody isotype that is produced in response to immunogen

Shorter half-life than IgG, concentration much lower in serum than IgG

5-10%

Pentamer, 2 subunits are joined to an intervening peptide= J chain (less stable because pentamer)

Can bind 10 antigens

Active in primary immune response

IgA

Serum IgA= structure similar to IgG.

Primarily exists in monomers 10-15%. There are 2 subclasses with heavy chains coded by alpha 1 and 2

Secretory IgA= exocrine systems (breast milk)

Covalently linked by disulfide bond to a J chain to create a dimer.

First line of defense at all mucosal surfaces and works well in neutralizing virus

IgD

exists as monomer in serum at very low concentrations

Primary expressed as a transmembrane molecules on surface of B cell

Dont know what it does

IgE

Exists as a monomer in serum at low concentrations

Allergic responseutralizing virus