The document discusses the structure, complexity, and function of immunoglobulins (antibodies), explaining their composition as Y-shaped globular proteins produced by plasma cells. It details the types of immunoglobulins, including their heavy and light chains, and introduces hypervariable regions critical for antigen binding. Additionally, the document outlines the various roles of immunoglobulins in immune response, such as neutralization, opsonization, and complement activation.

1. Lecture-10
IMMUNOGLOBULINS : Structure and Function
Prof. Sreerama Krupanidhi
Email: sknbirac@gmail.com

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Objectives
• To familiarize with the structure, complexity
and nature of antibodies/immunoglobulins.
• To understand the functions of various
regions of the assembled protein namely
Igs.

3. Expected Outcomes
• The nature of Immunoglobulin will be
known.
• The detailed structure of
Immunoglobulin as deciphered by
Porter and Edelman will be
familiarised.
• The assembled Y-shaped structure of
Ig will be acquainted.
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What are Immunoglobulins?
• Immunoglobulins are defence
serum glycoproteins produced by
Plasma cells upon elicitation of
Immune response against the
epitopes of an antigen/pathogen.
• Immunoglobulins are Y-shaped
globular assembled serum
proteins involved in host defence..

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Which cell produces Igs?
Igs are synthesised by the
plasma cells.
Constitutes 20-25% serum
proteins.
•5 classes of Igs – IgG, IgA, IgM,
IgD & IgE based on the H-
chain.
•They are called Isotypes.

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Symmetry in Ig
• Two pairs of polypeptide chains:
• Two Light chains on either side.
Each with 25,000 Daltons
• Two Heavy chains on either side.
Each with 50,000 Daltons.
• Both the L and H chains are
bound by disulphide bonds.

7. Shape & Structure of Immunoglobulin
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8. Shape & Structure of Immunoglobulin
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9. Shape & Structure of Immunoglobulin
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Hyper variable regions

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Hyper variable regions

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Hyper variable regions
•Amino acid sequence in the variable region
of L & H chains are not uniformly variable
•Consists of some highly variable
(hypervariable) and some relatively
invariable zones
• Highly variable zones actually make contact
with the epitope on an Ag and are called as
Complementarity Determining Regions
(CDRs)
• 3 CDRs – each made up of 9 -12 amino
acids.
• CDR3 is the longest & most variable of the
three

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Amino acids L and H chains of IgG

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Types of Light chains of IgG
• Light Chain is of two types:
• kappa () & lambda ( )
 .
• Each molecule of IgG is having
either () or( )
 .

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H-Chain : Isotypes and Subtypes of Igs
Isotype (Ig
Class)
H-Chain Subtypes
IgG  IgG1, IgG2,
IgG3 and IgG4
IgM 
IgA  IgA1 and IgA2
IgD 
IgE 

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Structure of IgG
Light chain contains: TWO regions
– Variable region (VL) N-terminal
– Constant region (CL) C-terminal
Heavy Chain Contains: THREE regions
– CH1, CH2, and CH3
Ig contains TWO fragments
– Fab and FC

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Y- Shaped structure
Porter and Edelman
Mercaptoethanol
reduction
1929-2014 1917-1985
Nobel Prize in the year 1972
Molecular structure of Abs

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Functions of fragments of IgG
• Fab Fragment – Ag binding.
• Fc fragment - Determines the biological
properties of Ig molecule.
• Receptors for Fc Fragments are
expressed On:
– Neutrophils
– Eosinophils
– NK cells
– Mast cells

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Functions of IgG
• Neutralization
– Direct inactivation of pathogen or toxin
thereby preventing its interaction with
human cells
• Opsonization
– Coating of pathogens for more efficient
phagocytosis
• Activation of complement
– More efficient phagocytosis
– Direct killing

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Various functions of Igs

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Summary
• The structure of assembled Y-shaped
Igs containing Fab and Fc regions along
with L and H Chains are highlighted.
• The tailored hypervariable regions of Igs
in the Fab region that bind to epitopes
of the antigens are familiarized .
• The functions of immunoglobulins to
eliminate pathogens are visualized.

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Study Questions
1. Draw a neat labeled diagram of IgG. Deduce
imolecular weight of fragments of Igs using
pepsin and papain.
2. Indicate the number of amino acids present in
each Chain of Ig.
3. What are hypervariable regions? Indicate their
functions.
4. What are the divisions of H and L chains?
5. What are the immune roles of Fab and Fc
fragments of Ig?

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Acknowledgements
We acknowledge the online resources
and public domains for the Preparation of
the content to develop teaching material
and for the dissemination of knowledge.

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