ANTIBODY STRUCTURE

give a simple description of the structure of an antibody

a y shaped protein made of 2 identical heavy chains and 2 identical light chains

what is the antibody variable region

the ends of the Y region which recognise the epitope of an antigen

do variable binding regions on one antibody differ

no, variable binding regions are identical

what are the 2 types of light chain

kappa and gamma

what are the different heavy chain constant regions for each antibody type

Ch 1 - 3 for IgG,A,D

Ch 1 - 4 for IgM,E

what are all the regions of an antibody

heavy chain

light chain

constant regions

variable regions

disulphide bonds

which antibodies have a hinge region

IgG, A, D

which antibodies have no hinge region

IgM, E

what does not having a hinge region mean in terms of epitope binding

no hinge means the antibody is rigid and stuck

this means either epitopes are perfectly distanced for both binding regions to bind, or only 1 will bind

list what each Immunoglobulin stands for

IgM → Mu

IgA → alpha

IgD → delta

IgG → gamma

IgE → epsilon

how are antibody heavy regions distinguished

by the varied content of the constant region between different antibody classes

what results from enzymatic digestion of anitbodies with papain

2 Fab fragments

Fc portion

what does Fab fragment stand for

Fragment antigen binding

What does Fc portion stand for

Fragment crystallisation

what does enzymatic digestion of antibody with pepsin result in

1 F(ab’)₂ fragment

what does reduction of disulphide bonds with mercaptoethanol result in

produces 2 separate light chains and 2 separate heavy chains

which 2 immunoglobulins have subclasses

IgG and IgA

what are the subclasses of IgG

IgG₁,_2,3,4

how do IgG subclasses occur

due to variations in the number of disulphide bonds in the heavy chain

what are the subclasses of IgA

IgA_1,2

Can immunoglobulins be immunogenic

Yes, immunoglobulins have epitopes which may induce an immune response in other individuals or species

what are the 3 types of antigenic determinants on antibodies

isotypic

allotypic

idiotypic

explain an isotypic epitope

epitopes on constant regions of both heavy and light chains of an antibody class that are same within a species

may vary between Ig classes within species

explain an allotypic epitope

epitopes on constant regions of both heavy and light chains of an antibody class that vary between individuals of same species

explain idiotypic epitopes

epitopes present on variable region of heavy and light chains

variation between antibody molecules of same class/subclass in an individual

define antibody valency

the number of binding/contact points between an antigen and antibody molecule

e.g. monovalent, divalent, polyvalent

define antibody avidity

the overall strength of binding between antigen and antibody due to number of contact points

describe the relationship between valency and avidity

avidity is directly proportional to valency

define antibody affinity

the strength of binding between 1 antibody binding site and 1 epitope

what forms in a zone of antibody excess

small complexes

what forms in the zone of equivalence

large complexes

what forms in a zone of antigen excess

small complexes

what can large complexes in vivo result in

diseases like rheumatic fever, glomerular nephritis etc

what happens to B cells upon primary exposure to antigen

naive mature B cells will differentiate into plasma cells or memory B cells

describe the function of plasma cells

they produce and secrete antibodies

which antibodies need T helper cell assistance to be made

IgA, G, E

describe the function of memory B cells

they express antibody on their surface and can produce antibodies upon reactivation when reinfection occurs

what are the 2 types of memory B cells

long lived

short lived

describe short lived memory B cells

they only produce IgM with no T cell help

describe long lived memory B cells

they turn into plasma cells make either IgA or E, with help of Th cells

which antibody predominates in the primary response

IgM

which antibody predominates in the secondary response

IgG