antibodies

also known as immunoglobulins

they r proteins synthesised by b lymohocytes

they r very specific → each antigen has its own antibdy

antibodies have a binding site that fits very precisely onto the antigen to form an antigen- antibody complex

antibdoes a specialised protein manufactured by plasma cells which can bind to and help neutralise foreign antigens

they can be free in the blood (or tear fluid) or used as receptors on the surface of white blood cells

antiobody strucure

composed of 4 polypeptide chans

→ 2 heavy chains

2 light chains

joined by disulphide bonds

form y shaped structure

the stem= constant region

the arms= variable regions that bind to antigen

scientists use this antibody to detect an antigen on the bacterium that causes stomach ulcers. explain why the antibody will only detect this antigen (3 marks)

→ antibody has specfic amino acid sequence/primary structure

the shapee/ tertiary structure of the binding site comp;ementary to/fits/ binds w these antigens

form antigen antibody complex

WHAT ANTIBODIES DO:

what is agglutination → antibodies with more than one bindng site can stick lots of pathogens together. this can stop them spreading throughout the body or makes them too large to enter cells

neutralisation → by attaching to binding sites on the pathogen, the antibody can prevent the pathgen from binding tp the host cells, stopping them from enetering. they may also neutralise toxins secreted by th pathogen in the same way

Increase phagocytosis by coating the pathogen in antibodies, it makes it easier for the phagocytes to bind to and engulf them

cell ysis → some antiodies can work w other molecules to’punch;’ holes in the pathigens cell walls. they will then burst when they take on water by osmosis (Lysis)

reduce mobility by attaching to the flagela of bacteria, antibodies can make them ess active and so reduce ability of the bacteria to move around

monoclonal antibodies → a specofoc antibody that could be made in the lab→ antibodies prodiuced from cloned plasma cells / antidoes w the same tertiarystrucrture

they ca be used for different reasons :

pregnancy tests

medical treatment eg cancer treatment

medical diagnosis

you have direct and indirect monoclonal antibodies

direct monoclonal antibody therapy - some cancer can be treated using monoclonal antibodies which are desgned with a bnding site complemetar in shape to the antigens on the outside f cancer cells

the antbodies are given to the cancer patientand attach to the cancer cells. while the antibodies are bound to the cancer antigwns, this prevents chemicals binding to the cancer cells which enable uncontrolled cell division

theredore the monoclonal antivodies prevent cancer cells growing, and as they r designed to only attach to cancer cells, they do not cause ham to other normal cells

they may not destrou cancer, it revnts it from growing

indirect monoclonal antibody therapy

cancer an also be treated with mnoclonal antibodies complimnetray in shape to the antiigens n the outside of cancer cells which hae drus attached to them

this cancer drugs ar theredore delivered dirctly to the cancer cellsand kill them. this reduces the harmful side effects that traditioal chemotheerapy and radiotherapy can produce

this is often referred to as ‘bullet drugs.

pregnancy tests

the application area will contain antibodies that are complimentary to the hCG antigen .

when combined, an antigen antibody complex will form

the antibody is bound to a coloured bead which willthen begin to move down the test strip

the antigen-antibody complex will bind to a second immobilised antibody. this new complex will remain in position, forming a blue line

some antidodies will not bind to the hCG antigen. they will continue past the immobilised antinody, fomrning a second control line. a single control line will also be preset if no hcg was present in the sample, indicating the indicual was not pregnant

pregnant women priduce hcg hormoe that ca be found in urine (and blood)

antibody will bind to hcg hormone

ELISA testing

→ testing for the presence of antibodies can be done using an enzyme-linked immunosorbent assay (ELISA)

elisa testing is used for medical diagnosis

it is often used to see if a patient is suffering from a pathogenic infection.

it ca also be used to test for allergies to certain compounds

in elisa testing, antibodies are bound to enzymes

this enzyme will react

elisa test (indirect)

add the test sample from patienet to the base of the beaker

wash to remove any unbound test sample

add an antibody comlimentary in shape to the antigen you are testing the presence of in the test tube

wash to remove any unboud antibody

add a second antibody that is comlimentary in shape to the first antibody and binds ti the first antiobdy

the second antibody has an enzyme attached to it

the substrate for the enzyme, which is colourless, is added. this substrate produces coloured products in the presence of the enzyme

the presence of the colour indiated the resencee of the antigen in the test samle and the itensity if th ecolour indicated the quanitiy (of antigens/pathigens) present

in direct elisa testing, involed thee use of a single antobody

monolonal antibodies that are comolementary to the antigen are added

the antibody has an enzyme attached to it

a coloured substrate solution is then added. is the complex is present, the enzyme will break down the substrate and the colour of the solution will change

indirevt elisa involved the use of 2 antbodies

ethics of monoclonal antibodies

monoclonal antibodies r often produed suing animals

in rder to make monoclonal antibodies, a mouse is injected with ana antigen

the mouse then crear=ted antibodies to counteract this antigen

tje antibodies are thrn removed frin the mouse using surgery

many people disagree with this on grounds of animal cruelty