[5.5] antibodies

Question 1

describe the structure of antibodies (draw and label a diagram)

Answer 1

shaped like a Y?

Question 2

in what way does an antibody bind to an antigen?

Answer 2

• forms an antigen-antibody complex
• can hold multiple antigens at the same time

Question 3

what are antigens made up of?

Answer 3

• proteins
• 4 polypeptide chains
• therefore, they have a quaternary structure

Question 4

what chains and bonds do antibodies have?

Answer 4

• 2 light chains and 2 heavy chains
• they are held together by strong covalent disulfide bonds

Question 5

what are the constant and variable regions?

Answer 5

• constant region is the part of each chain which will have exactly the same primary structure for all antibodies
• variable region is the other part of each chain which will have a different specific sequence of amino acids for each specific antibody

Question 6

what type of structure does the variable region have?

Answer 6

the variable regions each have a specific tertiary structure which form the 2 antigen binding sites

Question 7

what is agglutination?

Answer 7

• when antibodies bind to multiple antigens, therefore forming large clumps, which immobilises them
• this makes it easier for phagocytes to destroy them through phagocytosis

Question 8

how do you obtain monoclonal antibodies? [8]

Answer 8

1. inject animal with antigen
2. leave time for immune response
3. harvest B cells from spleen
4. fuse B cells with myeloma cells to form hydridomas
5. grow hydridomas in petri dish - rapid mitosis due to high myeloma cell dvision rate
6. test for production of desired antibody and isolate
7. culture desired B cell
8. harvest and purify antibodies

NB: ethical considerations?

Question 9

why can MAbs be used in cancer treatment?

Answer 9

• cancer tumour cells have specific antigens on their surface
• specific complementary MAbs can bind to these antigens, destroying cancer cells by various means

Question 10

how can MAbs be used in cancer treatment? (3)

Answer 10

1. targeted delivery of anti-cancer drugs (indirect MAb therapy)
2. signalling to cell -> apoptosis or prevention of cell cycle (direct MAb therapy)
3. bringing macrophage / natural killer cell directly to the tumour

Question 11

how can MAbs be used in pre-emptive treatment?

Answer 11

to give passive artificial immunity if potentially exposed to a new dangerous pathogen eg. rabies virus

Question 12

what can monoclonal antibodies be used to diagnose?

Answer 12

• influenza
• hepatitis
• chlamydia
• cancers eg. prostate cancer
• pregnancy
• HIV

Question 13

how are monoclonal antibodies utilised in pregnancy tests?

Answer 13

• the placenta produces a hormone called hCG, which can be found in the mother’s urine
• MAbs present on the test strip are linked to coloured particles
• if hCG is present in the urine it binds to these antibodies
• the hCG-antibody-colour complex moves along the strip until it is trapped by a different type of antibody creating a coloured line

Question 14

ethical issues of monoclonal antibodies

Answer 14

• production of MAbs involves deliberately inducing cancer in mice
• there have been some deaths associated with their use in the treatment of multiple sclerosis
• in march 2006, six healthy volunteers took part in a trial of a new MAb. within minutes, they suffered multiple organ failure