5 cell recognition and immune system

Question 1

state 2 ways pathogens can cause harm

Answer 1

pathogens can produce toxins that damage tissue
pathogens can replicate inside and destroy host cells

Question 2

what can the molecules on the plasma cell surface membrane identify?

Answer 2

pathogens
abnormal body cells
toxins
cells from other organisms of the same species

Question 3

what is an antigen?

Answer 3

an antigen is a molecule that stimulates an immune response that results in the production of a specific antibody

Question 4

what happens if antigens on a cell are not recognised?

Answer 4

the body will treat the cell as non self and initiate an immune response. this will destruct the cell

Question 5

what are phagocytes?

Answer 5

groups of white blood cell

Question 6

what does a phagocyte do?

Answer 6

1. pathogen engulfed by phagocyte
2. pathogen enters the cytoplasm of the phagocyte in a vesicle which is now called a phagosome
3. lysosomes fuse with phagosome releasing lysozymes
4. lysozymes hydrolyse pathogen
5. waste materials are released by exocytosis and antigens are presented on the membrane making the pathogen an APC

Question 7

what type of process is phagocytosis?

Answer 7

non specific.

Question 8

what does non specific mean?

Answer 8

works the same for any cell that displays a non self antigen

Question 9

why does phagocytosis not work all the time?

Answer 9

non specific so would take too long to destroy all pathogens in an infection resulting in damage to tissues and organs

Question 10

what is a specific response?

Answer 10

specific to certain antigens or pathogens that have been recognised as non self

Question 11

what are the 2 types of specific immunity?

Answer 11

cell mediated
humoural

Question 12

what are the 3 stages of the cell mediated response?

Answer 12

1. antigen presenting
2. clonal selection
3. role of t cells

Question 13

describe antigen presenting stage of cellular response.

Answer 13

TH cells respond directly to specific pathogen or respond to APC (from phagocytosis) that presents specifically complementary antigen

Question 14

explain clonal selection as a part of the cellular response

Answer 14

1. specific TH cell binds to presented antigen via its complementary receptor
2. TH cell activated and clones by mitosis (produces cells with complementary receptors to the antigen)

Question 15

what is the role of a TH cell?

Answer 15

1. binds to antigen on presenting cell
2. releases cytokines that attract phagocytes and activate Tc cell
3. activates specifically complementary B cell
4. form memory Th cells

Question 16

what is a Tc cell?

Answer 16

cytotoxic killer cell

Question 17

what is the role of a Tc cell?

Answer 17

1. locate and destroy infected body cell
2. binds to APC
3. releases perforin which created holes in the cell surface membrane

Question 18

how are B cells activated in the humoral response?

Answer 18

1. specific TH cell binds to APC and locates and activates a specifically complementary B cell
2. TH cell releases cytokine that signals the B cell to clone by mitosis

Question 19

what happens when the B cell clones by mitosis?

Answer 19

B cell differentiates into
plasma cell or memory B cell

Question 20

what do plasma cells do?

Answer 20

produce and secrete vast quantities of specific antibodies into blood plasma

Question 21

what do memory B cells do?

Answer 21

remain in body to respond to pathogen rapidly in case of future infection

Question 22

what is an antibody?

Answer 22

a protein made in response to a foreign antigen

Question 23

what is a specific antibody produced by?

Answer 23

specific plasma cell

Question 24

describe the antibody structure

Answer 24

• complex protein with 4° structure
• 4 polypeptide chains
• Y shaped
• constant region
• variable region
• antigen binding site
• peptide bonds and disulphide bridges

Question 25

what is the constant region of an antibody?

Answer 25

the main part which is the same in all antibodies

Question 26

what is the variable region in an antibody?

Answer 26

have a different 1° and 3° structure binding site specific which is different for each antibody

Question 27

antibodies have specific binding sites. what does this lead to?

Answer 27

they can only bind to specific antigens forming an antibody antigen complex

Question 28

how do antibodies assist destructing pathogens?

Answer 28

1. agglutination 2. opsonisation 3. lysis 4. anti toxin and anti venom 5. prevent pathogen replication

Question 29

what does agglutination mean referring to antibodies?

Answer 29

specific antibodies bind to antigen on pathogen and clump them together

Question 30

what does opsonisation mean referring to antibodies?

Answer 30

mark pathogens so phagocytes recognise and destroy pathogen efficiently

Question 31

what does lysis mean referring to antibodies?

Answer 31

bind to antigen and lead to destruction of pathogens membrane

Question 32

what does anti toxin and anti venom mean referring to antibodies?

Answer 32

binds to toxins or venom to prevent these molecules from binding to complementary target receptors

Question 33

what happens if B memory cells encounter the antigen again?

Answer 33

1. they are rapidly activated by cytokines (TH cell) and divide rapidly by mitosis 2. clone into plasma cells and more memory cells 3. plasma cells produce lots of specific antibodies for the pathogen QUICKLY

Question 34

what is the secondary response?

Answer 34

the activation of memory cells to produce antibodies

Question 35

why don’t some illnesses like HIV initiate a secondary response?

Answer 35

antigens mutate and change shape so pathogen will not be recognised and secondary response can’t be initiated. (antigenic variability)

Question 36

which two ways can immunity be gained?

Answer 36

active passive

Question 37

what is passive immunity?

Answer 37

antigens aren’t produced by individual so no production of memory cells

Question 38

what is active immunity?

Answer 38

antibodies produced in exposure to antigen so memory cells are produced

Question 39

give an example of passive immunity

Answer 39

vaccine

Question 40

how do vaccines work?

Answer 40

1. vaccines contain antigens from dead weakened or attenuated pathogens 2. body carries out non specific and specific immunity

Question 41

what are vaccines not effective against?

Answer 41

pathogens that show antigenic variability

Question 42

define herd immunity

Answer 42

if enough individuals in the population are vaccinated (85%), there is little chance of the disease spreading and even non vaccinated individuals will be protected

Question 43

give 6 ethical issues associated with vaccines

Answer 43

1. animal testing 2. human testing 3. availability to all countries 4. side effect risks 5. should they be compulsory? 6. should we be aiming to eliminate an organism?

Question 44

explain the elisa test

Answer 44

1. monoclonal antibodies fixed to surface of test well 2. sample containing X binds to complementary antibody 3. more monoclonal antibody and enzyme attached added and binds to X 4. washed so any unbound antibodies removed 5. substrate added- colour change

Question 45

describe the structure of HIV

Answer 45

- HIV envelope - HIV capsid - HIV enzymes - HIV RNA - attachment protein

Question 46

what is the role of the capsid in HIV?

Answer 46

contains HIV RNA

Question 47

how does HIV replicate?

Answer 47

1. attachment protein binds to protein on TH cells 2. capsid fuses with membrane and releases viral RNA and enzymes into T cell 3. HIV’s reverse transcriptase converts RNA into cDNA 4. viral cDNA enters nucleus of T cell and inserted into the DNA 5. transcription leads to translation of HIV proteins 6. reduces number of TH cells

Question 48

how does HIV lead to symptoms of AIDS?

Answer 48

HIV reduces the ability to respond to pathogens as their cell mediated immunity is compromised so they have less TH cells symptoms: infections, weight loss, diarrhoea

Question 49

how do antibiotics work?

Answer 49

prevent bacteria from making a normal cell wall by targeting 70s ribosomes bacteria unable to resist osmotic pressure so burst

Question 50

why don’t antibiotics act on viruses?

Answer 50

viruses don’t have a cell wall (capsid instead)