22 Questions
Binding can activate the cells to perform some biological ______.
functions
IgG constitutes about ______% of total Igs of the body.
70-80
IgG has the longest ______-life of 23 days.
half
IgG has four subclasses- IgG1, IgG2, IgG3 and ______.
IgG4
IgM has the highest ______ weight, and maximum sedimentation coefficient (19S).
molecular
IgM exists in both ______ and pentameric forms.
monomeric
IgA constitutes about ______% of total serum Ig.
10-15
Dimeric IgA is composed of two ______ units joined by a J chain.
IgA monomeric
An antibody is a specialized ______ produced from activated B cells
glycoprotein
Antibody and ______ are used interchangeably to represent the physiological and functional properties of the same molecule
immunoglobulin
There are five classes of ______ recognized: IgG, IgA, IgM, IgD, and IgE
immunoglobulins
An antibody molecule is a ______ shaped heterodimer composed of four polypeptide chains
Y-shaped
The ______ region represents the antigen binding site of the antibody
variable
Antibody coating the target cell binds to ______ through its Fc receptor
complement
Phagocytic cells, lymphocytes, platelets, mast cells, NK cells, eosinophils, and basophils bear ______ receptors that bind to the Fc region of immunoglobulins
Fc
Each H and L chain has two ends: an ______ terminal end and a carboxyl terminal end
amino
Secretory IgA provides good protection to the immunologically immature infant ______.
gut
IgA exists in two ______ isotypes: IgA1 and IgA2.
subclasses
IgE is the only ______ labile antibody, inactivated at 56º C in one hour.
heat
IgD is found as membrane Ig on the surface of ______ cells and acts as a B cell receptor.
B
The five classes of Igs and their subclasses are called as ______.
isotypes
Isotypic variation refers to the variation in the amino acid sequences of the constant region of their ______ chains.
heavy
Study Notes
Antibody Structure
- An antibody molecule is a 'Y-shaped' heterodimer composed of four polypeptide chains: two identical light (L) chains and two identical heavy (H) chains.
- The molecular weight of L chains is 25,000 Da each, and H chains have a molecular weight of 50,000 Da or more.
- The chains are bound together by disulfide bonds and noncovalent interactions.
Antibody Regions
- Each H and L chain consists of two regions: variable and constant regions.
- The variable region represents the antigen binding site of the antibody.
Functions of Immunoglobulins
- Effector functions are mediated by the Fc region, including fixation of complement, binding to various cell types, and activation of cells to perform biological functions.
- Immunoglobulins can cross the placenta and provide immunity to the fetus and newborn.
Immunoglobulin G (IgG)
- Constitutes about 70-80% of total Igs in the body.
- Has the longest half-life of 23 days and the highest serum concentration.
- IgG has four subclasses: IgG1, IgG2, IgG3, and IgG4, which differ in their biological functions, hinge region length, and number of disulphide bridges.
- Functions: crosses placenta, provides immunity to fetus and newborn, fixes complement, mediates phagocytosis, and neutralizes toxins.
Immunoglobulin M (IgM)
- Has the highest molecular weight and sedimentation coefficient (19S).
- Exists in both monomeric and pentameric forms.
- Functions: provides immediate immunity, fixes complement, acts as an opsonin, mediates agglutination, and is an antigen receptor.
Immunoglobulin A (IgA)
- Exists in both monomeric and dimeric forms.
- Secretory IgA provides local or mucosal immunity, effective against bacteria and viruses, and is found in body secretions like milk, saliva, tears, and intestinal and respiratory tract mucosal secretions.
Immunoglobulin E (IgE)
- Has the lowest serum concentration, shortest half-life, and minimum daily production.
- Is heat-labile and has affinity for the surface of tissue cells, especially mast cells.
- Mediates type I hypersensitivity reactions and is elevated in helminthic infections.
Immunoglobulin D (IgD)
- Is found as membrane Ig on the surface of B cells, acting as a B cell receptor along with IgM.
- Has the highest carbohydrate content among all the Igs, but its functions are unknown.
This quiz covers the basics of antibodies, also known as immunoglobulins, which are specialized glycoproteins produced by activated B cells in response to an antigen. Learn about their structure, function, and role in the immune system.
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