the immune system

Question 1

what is a pathogen?

Answer 1

a disease causing organism

Question 2

what is an antigen?

Answer 2

● a protein / glycoprotein on surface of a cell / pathogen

● that triggers an immune response

Question 3

what are the types of antigens?

Answer 3

● self

● non-self

Question 4

what causes antigen variability?

Answer 4

● antigens can change shape due to mutations in DNA base sequence controlling the antigenic protein structure

● results in different sequence of codons on mRNA

● different primary structure of antigen - hydrogen bonds, ionic bonds and disulfide bridges form in different places in tertiary structure

● different shape of antigen

Question 5

what is antigenic shift?

Answer 5

● larger changes to the antigen structure that don’t compliment previous memory cells

● doesn’t trigger a secondary response

Question 6

what is antigenic drift?

Answer 6

● minor changes in antigen structure that can still trigger a secondary response

● affected by previous memory cells

Question 7

explain how antigen variability affects incidence of disease (3)

Answer 7

● memory cells no longer complementary to antigen

● individual not immune

● can catch the disease again / more than once

Question 8

what is an antibody?

Answer 8

● a protein produced / secreted by lymphocytes

● quaternary structure: 2 light chains, 2 heavy chains

● held together by disulfide bridges

● binding sites on the variable region of light chains have specific tertiary structures complimentary to antigen - allow antibody to bind to it

● rest of the molecule is known as the constant region
(all antibodies have same shaped constant region)

Question 9

what is a lymphocyte?

Answer 9

● wbc

● produces antibodies and antitoxins

Question 10

what is a phagocyte?

Answer 10

● wbc

● engulfs and digests pathogen

Question 11

what is a disease?

Answer 11

the malfunction of part or whole of the body with a characteristic set of symptoms

Question 12

what is the immune response?

Answer 12

● a complex series of responses in body to the entry of a foreign antigen

● involves activity of lymphocytes and phagocytes

Question 13

what is phagocytosis?

Answer 13

● when a phagocyte engulfs a pathogen and destroys it

● an example of endocytosis

Question 14

how does phagocytosis destroy pathogens? (5)

Answer 14

● pathogens have non-self antigens which trigger an immune response

● phagocyte engulfs pathogen, via endocytosis, forming a phagosome

● lysosome fuses with the phagosome forming a phagolysosome

● pathogen is digested / hydrolysed by hydrolytic enzymes

● pathogen debris is released by exocytosis

Question 15

explain the role of antigen-presenting cells (APCs)

Answer 15

● pathogens antigen becomes presented on surface - phagocyte becomes an APC (after hydrolysis in phagocytosis)

● enhances recognition by t helper cells

● which can not directly interface with pathogens / antigens

Question 16

what are the difference between specific and non specific immune responses?

Answer 16

● non-specific (phagocytosis) - same for all pathogens, immediate

● specific (B & T lymphocytes) - complimentary pathogen, time lag

Question 17

what are the 2 types of specific immune responses?

Answer 17

● cell-mediated

● humoral

Question 18

outline the process of the cell-mediated response (5)

Answer 18

● complimentary specific receptor on t helper cell binds to presented antigen

● t helper cells are then activated which cause mitosis

● clones differentiate into cytotoxic t killer cells

● t killer cell binds to infected host cell and secretes enzyme perforin (which pokes holes in cell membrane)

● infected cell will lyse (burst)

Question 19

outline the process of the humoral response (5)

Answer 19

● complimentary specific receptor on t helper cell binds to presented antigen

● t helper cells are then activated which cause mitosis

● clonal selection occurs and t helper cell activates complimentary b cell

● clonal expansion (mitosis of activated b cell) occurs

● clones differentiate into b plasma cells or b memory cells

Question 20

what are the types of lymphocytes?

Answer 20

● B cells (mature in bone marrow)

● T cells (mature in thymus)

Question 21

where are lymphocytes released and found?

Answer 21

in the lymphatic system

Question 22

what are the type of B lymphocytes?

Answer 22

● B plasma cell

● B memory cell

Question 23

what are the type of T lymphocytes?

Answer 23

● T helper cell

● T killer cell

● T memory cell (don’t need to know)

Question 24

what do B plasma cells do?

Answer 24

● makes and secretes antibodies

● can’t divide by mitosis

Question 25

what do B memory cells do?

Answer 25

● can divide by mitosis ● live a long time ● can't secrete antibodies ● when activated they can differentiate into plasma cells

Question 26

what do T helper cells do?

Answer 26

● activates other cells in immune system ● activated themselves by APCs or by the pathogen ● when activated will divide by mitosis and differentiate into killer cells, memory cells and more helper cells

Question 27

what do T killer cells do?

Answer 27

● cytotoxic ● releases chemical that kills infected host cells

Question 28

how do antibodies lead to the destruction of a pathogen?

Answer 28

● formation of antigen-antibody complex ● resulting in agglutination ● enhancing phagocytosis

Question 29

what is agglutination?

Answer 29

● antibody binds to antigen on pathogen ● clumps them together

Question 30

what are monoclonal antibodies?

Answer 30

● an antibody produced from identical plasma cells ● with the same tertiary structure

Question 31

contrast the primary and secondary immune response

Answer 31

● secondary response: - faster rate of antibody production - shorter time lag between exposure and antibody production - higher concentration of antibodies - antibody level remains higher after secondary response - pathogen usually destroyed before any symptoms - clonal selection is much faster - more extensive ● primary response: - slower rate of antibody production - longer time lag between exposure and antibody production - lower concentration of antibodies - experience symptoms - clonal selection is slower

Question 32

what is active immunity?

Answer 32

where antibodies are produced by a persons plasma cells

Question 33

what is passive immunity?

Answer 33

where immunity is gained with no immune response

Question 34

compare active and passive immunity

Answer 34

● both involve antibodies ● can both be natural or artificial - passive natural: antibodies passed by breast milk / across placenta - passive artificial: antibodies injected in ig therapy - active natural: humeral response to infection - active artificial: vaccination

Question 35

contrast active and passive immunity

Answer 35

● active: - memory cells produced - long term - time lag - lymphocytes produce antibodies - direct contact with antigen necessary ● passive: - no memory cells produced - short term - immediate - antibodies from external source - direct contact with antigen not necessary

Question 36

explain vaccination

Answer 36

● vaccine contains inactive pathogen / antigen ● triggers primary immune response ● memory cells are produced and remain in blood stream ● so, secondary response is rapid and produces higher conc of antibodies ● pathogen is destroyed before it causes symptoms

Question 37

what is herd immunity?

Answer 37

● vaccinating large proportion of population reduces available carriers of the pathogen ● protects individuals who have not been vaccinated (e.g. those with a weak immune system)

Question 38

suggest some ethical issues surrounding the use of vaccines

Answer 38

● production may involve use of animals ● potentially dangerous side effects

Question 39

describe the structure of HIV

Answer 39

● RNA genome ● reverse transcriptase (unique to HIV) - converts single stranded RNA genome of HIV into double stranded DNA ● surrounded by capsid (protein coat) ● surrounded by envelope (lipid) - a phospholipid bilayer derived from the host cell's cell surface membrane ● attachment proteins on surface: - act as an antigen to host's immune system - attach to get into host cells (t helper) ● NOT a cell (acellular)

Question 40

how does HIV replicate?

Answer 40

● attachment proteins attach to a receptor molecule on cell membrane of t helper cells ● capsid is released into cell, where it uncoats and releases the RNA into cells cytoplasm ● reverse transcriptase is used to make a complimentary strand of DNA from viral RNA template ● double stranded DNA is made and inserted into human DNA ● host cell enzymes and ribosomes used to make viral proteins from the viral DNA found within the human DNA ● viral proteins assembled into new viruses which bud off and go to new host

Question 41

what cells to HIV particles infect?

Answer 41

● t helper cells ● affects immune response as fewer t helper cells means less / slower clonal selection and clonal expansion ● fewer specific and complimentary antibodies produced by b plasma cells

Question 42

when does AIDS develop?

Answer 42

when there is too few t helper cells for the immune system to function

Question 43

what are the clinical applications of monoclonal antibodies?

Answer 43

● pregnancy tests (detecting hCG hormone in urine) ● diagnostic procedures (e.g. ELISA test) ● targeted treatment by attaching drug to antibody that is specific and complimentary to abnormal antigen e.g. cancer ● detection (e.g. MaBs with radioactive marker attached)

Question 44

describe how monoclonal antibodies are used in pregnancy tests

Answer 44

● mobile monoclonal antibodies with coloured beads attached - complimentary to hCG ● test: immobilised monoclonal antibodies - complimentary to hCG ● control: immobilised monoclonal antibodies complimentary to antigen binding site

Question 45

what does ELISA stand for?

Answer 45

enzyme linked immunosorbent assay

Question 46

describe a direct ELISA test

Answer 46

● detects presence of a specific antigen ● antigens in host (from blood) bound to the bottom of well ● enzyme linked monoclonal antibodies added complimentary to specific antigen in host you are testing for ● wash out excess unbound enzyme linked MAbs ● add substrate to the enzyme linked to the antibody ● positive result: colour change

Question 47

describe an indirect ELIZA test

Answer 47

● detects presence of an antibody against a specific antigen ● antigen for disease being tested for bound to bottom of well ● patient / hosts blood plasma sample is added ● specific, complimentary antibodies in sample bind to antigen ● wash out excess antibodies ● secondary enzyme linked monoclonal antibodies added which are specific and complimentary to constant region of primary antibodies from sample ● wash out again to remove any unbound patient and enzyme linked antibodies ● add substrate to enzyme linked to MAbs ● positive result: colour change

Question 48

why is important to wash the well?

Answer 48

● to make sure colour change is accurate ● e.g. no false positives

Question 49

explain how hybridoma cells are produced

Answer 49

● antigen of interest injected into mouse ● results in immune response - mouse produces B plasma cells (constantly producing antibodies but can't divide by mitosis) ● produces antibodies complimentary to antigen of interest ● myeloma cell (skin cancer cell) - constantly dividing by mitosis ● B plasma cell and myeloma cell are hybridised (fused) ● to form a hybridoma cell (secretes antibodies and divides by mitosis) ● monoclonal antibodies can be isolated from hybridoma cells

Question 50

suggest an ethical issue surrounding the use of monoclonal antibodies

Answer 50

production involves animals

Question 51

why are antibiotics ineffective against viruses?

Answer 51

● antibiotics kill bacteria by interfering with their metabolic reactions ● antibiotics are only designed to target bacterial enzymes and ribosomes ● viruses don't have their own enzymes and ribosomes ● therefore, antibiotics can't inhibit them

Question 52

outline differences between active and passive immunity (6)

Answer 52

Active involves memory cells, passive does not, Active involves production of antibody by plasma cells / memory cells; Passive involves antibody introduced into body from outside / named source; Active long term, because antibody produced in response to antigen; Passive short term, because antibody (given) is broken down; Active (can) take time to develop / work, passive fast acting.