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Protection against
Disease
Antibody Structure and Function
Learning Objectives
Describe structure and function of
antibodies
 Explain the role of antibodies in
immune responses
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Starter Activity
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Crossword
Structure
Antibodies are molecules synthesises
by animals in response to the
presence of a foreign substance
(antigen)
 They are made by B lymphocytes
 Antibodies are proteins found in
plasma, tissue fluid and milk
 They are also called Immunoglobins
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Structure
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They are globular proteins make up of 4 polypeptide
chains- 2 light (short) MM =23000 chain and 2 heavy
(long) Mm= 50-60000 chains
All immunogloblins within a particular type have a
similar structure for part of their molecule called the
constant region. The region is highly variable. This the
part that interacts with antigens
The body is capable of making over million types of
antibody- to counteract almost any antigen
There is a 3D fit between the amino acid chain in the
antibody and the antigen
This is similar to that between an enzyme and
substrate-although not so precise
Method of Action
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Antibodies have 2 active sites each of which can combine
with a separate antigen molecule
This allows a number of antibody molecules to combine
with a number of antigen molecules to form a lattice
structure called an Antibody-Antigen complex
The AAC immobilises virus particles so they cannot latch
onto host cells
 The interlocking of and antibody and antigen could
render a toxic antigen harmless if its active region
was blocked by an antibody molecule
 Phagocytes can more easily track down and ingest
pathogens if they are immobilised in an AAC
 The AAC also stimulates the activation of a number of
plasma proteins. This leads to a substance called
complement binding with the complex and destroying
the pathogens by making cells rupture
 Sometimes some of the proteins cover the outer
membrane of the pathogens so phagocytes can
ingest them more easily. This preparation of
pathogens is opsonisation
Tasks