Antibodies

Question 1

Two different types of immune responses + definitions

Answer 1

innate- comprises of a genetically programmed set of responses that can be mobilised immediately upon infection

adaptive- immunity developed against one pathogen, providing a highly specialised defence

Question 2

What mediates the adaptive immunity response?

Answer 2

Specific antigen receptors that bind to antigens on or produced by pathogens

Question 3

different forms of antigen receptor

Answer 3

secreted or cell associated

Question 4

antigen definition

Answer 4

a molecule that elicits an adaptive immune response

Question 5

Immunoglobin definition

Answer 5

A large, Y shaped protein, produced mainly by plasma cells that is used by the immune system to neutralise pathogens and viruses, otherwise known as antibodies/ Ig

Question 6

two types of antibody

Answer 6

B-cell associated

secreted- soluble in humour

Question 7

What are T cell receptors?

Answer 7

protein complex found on the surface of T lymphocytes that are responsible for recognising antigens, however can never be secreted

Question 8

What produce antibodies?

Answer 8

plasma cells, that differentiate from B-cells

Question 9

Where are plasma cell sites for immunoglobulin synthesis?

Answer 9

gut, mammary gland, bone marrow, lymphoid organs

Question 10

Role of antibodies

Answer 10

Bind to micro-organisms and prevent their entry into cells

bind to organisms and also to cells

assists phagocytes- opsonisation- and helps phagocytes neutralise bacterial toxins

activates complement and induces inflammation

membrane bound immunoglobulins act as a receptor for antigens

Question 11

Explain binding to microorganisms

Answer 11

agglutination- antibodies glue together foreign cells into clumps that are attractive targets for phagocytosis

precipitation- antibodies glue together serum-soluble antigens, forcing them to precipitate out of solution into clumps that act as targets for phagocytosis

Question 12

explain neutralisation

Answer 12

antibodies bind to regions of the bacterial cell or virion surface, preventing it from being able to enter the cell, thus neutralising it

Question 13

define opsonisation

Answer 13

a molecular mechanism whereby molecules, microbes and apoptotic cells are chemically modified to have a stronger attraction to the cell surface receptors on phagocytes and natural killer cells

Question 14

how do opsonins aid phagocytosis?

Answer 14

cell membranes have a negative charge- Zeta potential, which results in the cells repelling

opsonins bind to their targets, boosting the kinetics of phagocytosis by favouring interaction between the opsonin and cell surface receptor

Question 15

inflammation definition

Answer 15

an ancient concept of medicine, that has been traditionally defined by the Latin words calor, dolor, rubor and tumor, heat, pain, redness and swelling

it is a result of the body’s working immune system and not the pathogen itself

Question 16

Antibody structure

Answer 16

a glycoprotein made with two heavy chains and two light chains, bound together by disulfide bridges

the N- termini V light and V heavy domains act as the variable region, which contains the binding site

the rest of the Y-shaped molecule forms the constant region

Question 17

Explain light chain structure

Answer 17

made of two domains Vlight and Clight which are formed of two different beta chains

Question 18

What is the constant domain?

Answer 18

the other C domains, that have little or no sequence diversity within a particular class of antibody

Question 19

What is the variable region?

Answer 19

the region where the polypeptide chains of different antibodies vary greatly in amino acid sequence

Question 20

What two fragments can be formed by cleaving the antibody + where?

Answer 20

cleaved at the hinge region using proteases papain and pepsin

form 2 Fab- fragment antigen binding, because they bind the antigen

form 1 Fc - fragment crystalisable, because it readily crystallises

Question 21

Fc function

Answer 21

mediates the effector functions of the antibody molecule by binding to serum proteins and cell surface receptors

formed of 4 constant heavy domains

Question 22

Hinge function of IgG

Answer 22

Allows the two Fab molecules to adopt different spatial orientations relative to one another, which enables antigens spaced at different distances apart on pathogens to be bound tightly by one IgG molecule

Question 23

Fab function

Answer 23

antigen binding region for specificity, formed of V light, V heavy, C light and C heavy

Question 24

What are the different classes of immunoglobulins?

Answer 24

IgG, IgM, IgD, IgA and IgE

Question 25

how are the different classes distinguished?

Answer 25

on the basis of structural differences in the heavy- chain constant part of the molecule which confer different effector functions on the isotopes

Question 26

What is the most abundant isotope + weights of different regions?

Answer 26

IgG

molecular weight of 150kDa

heavy chain: 50 kDa

light chain: 25 kDa

Question 27

what are immunoglobulin domains?

Answer 27

series of similar sequence motifs that fold into a compact and exceptionally stable protein domain- so the V heavy and C light are domains

Question 28

structure of a domain

Answer 28

two beta sheets held together by strong hydrophobic interactions between their constituent amino acid side chains

stabilised by a disulfide bond between the two beta sheets

adjacent stranded within the beta sheets are interconnected by loops of the polypeptide chain

Question 29

Structure of each isotype

Answer 29

IgG- heavy chain has three domains CH1, Ch2, CH3,

IgM- heavy chain has 4 domains, CH1,CH2,CH3,CH4

IgD- heavy chain has 3 domains

IgA- heavy chain has 3 domains

IgE- heavy chain has 4 domains

ME- self absorbed, wants the most so has 4

Question 30

what is the hyper variable region? + structure and location

Answer 30

region where the differences in amino acid sequence are particularly concentrated

three hyper variable regions are found in each V domain

exposed at the end of the domain farthest from the constant region

Question 31

what do the three hyper variable regions form + why?

Answer 31

the complementarity-determining regions, because they provide a binding surface that is complementary to that of a specific antigen

Question 32

what part of the antigen do the antibodies bind to?

Answer 32

the epitope- antigenic determinant

Question 33

what are isotype subclasses?

Answer 33

antibodies within the same wider class that differ in the constant region of the heavy chain, with many differences being in the hinge e.g IgG1, IgG2, IgG3, IgG4

Question 34

avidity definition

Answer 34

the overall strength of biding at multiple sites of the antibody

Question 35

3 different types of antibody complexes + which subtypes

Answer 35

monomer- IgG, IgE. IgD

dimer- IgA

pentamer- IgM

Question 36

High affinity Fc Ig

Answer 36

often pre bound to receptor- IgE on mast cells

Question 37

low affinity Fc Ig

Answer 37

IgG, IgA, IgE - the Fc receptor are only occupied once the antigen has bound to the antibody

Question 38

Important function of IgE

Answer 38

binds to mast cells and triggers degranulation

increases mucus secretion in airways

increases peristalsis in gut

increases blood flow and permeability- more lymph

Question 39

What cells degrade antigens?

Answer 39

neutrophils and macrophages

Question 40

where is IgA mainly found?

Answer 40

mucosal membranes, tears, salivar, colostrum, gut

Question 41

where is IgG mainly found?

Answer 41

placenta

Question 42

Unique function of IgG + why

Answer 42

it protects the uterus- easily permeate tissues

smallest antibody, so the only one that can permeate the placenta, thus can protect the neonate