Immunology

Question 1

define what an antigen is

Answer 1

a foreign molecule - usually a protein - that stimulates an immune response, resulting in the production of a specific antibody

Question 2

which types of molecules does the body class as ‘non-self’? (4)

Answer 2

pathogens

transplanted cells

abnormal body cells
- owing to viral infection
- having become cancerous

toxins

Question 3

“antigens will have a _________________________________ that is complementary to an _____________ or ____________ of an immune cell”

Answer 3

specific tertiary structure
antibody
receptor

Question 4

“the immune system can be divided into two broad arms that provide a ______________ and ______________ response”

Answer 4

non-specific
specific

Question 5

what occurs in the non-specific response of the immune system?

Answer 5

phagocytosis

Question 6

what can phagocytes do? (2)

Answer 6

• distinguish between cells that display self antigens and those that display non self antigens
• destroy any cell presenting non self antigens through phagocytosis

Question 7

describe the process of phagocytosis (5)

Answer 7

• phagocytes engulf pathogen
• this forms a vesicle called a phagosome
• phagocytes contain lysosomes, which fuse with the phagosome
• hydrolytic enzymes hydrolyse the pathogen
• exocytosis releases this debris

Question 8

what occurs in the specific response of the immune system?

Answer 8

phagocytosis
then
antigen presentation

Question 9

explain what antigen presentation is (2)

Answer 9

• when exocytosis occurs, the phagocyte keeps the attachment proteins
• it will then display these as its own antigens on its cell surface membrane

Question 10

“the specific response can then be further divided into the _____________ response and the _____________ response”

Answer 10

cellular
humoral

Question 11

explain the cellular response (4)

Answer 11

• initiated by antigen presentation
• t helper cells have a receptor that has a complementary shape to the antigen
• upon binding to the antigen, the t helper cells become activated and divide by mitosis
• they will then release cytokines

Question 12

what three things does the release of cytokines trigger to happen?

Answer 12

• stimulates b cells to divide by mitosis
• stimulates phagocytes
• stimulates cytotoxic t cells

Question 13

what type of cells do cytotoxic t cells target? (2)

Answer 13

• virally infected
• cancerous

Question 14

how do cytotoxic t cells operate? (2)

Answer 14

• upon binding to antigens, they release perforin which makes a hole in the cell surface membrane
• the cells will then undergo apoptosis (cell death)

Question 15

explain the humoral response (4)

Answer 15

• b cells can either be stimulated directly by the antigen binding to it, or by the release of cytokines
• they will divide by mitosis (“clonal expansion”)
• some will differentiate into plasma cells
• some will become memory cells

Question 16

what do plasma cells do?

Answer 16

produce and release large quantities of monoclonal antibodies into the blood

Question 17

what do memory cells do? (2)

Answer 17

• persist in the blood for years
• help to mount a faster immune response upon re-infection

Question 18

which part of the humoral response is the primary response, and which part is the secondary response?

Answer 18

primary response
the differentiation into plasma cells

secondary response
the differentiation into memory cells

Question 19

define what monoclonal antibodies are?

Answer 19

have the same tertiary structure produced by identical or cloned plasma cells

Question 20

what are monoclonal antibodies an example of?

Answer 20

a quaternary protein

Question 21

list the structural features of a monoclonal antibody (2)

Answer 21

• 4 polypeptide chains (2 heavy and 2 light) joined together by disulphide bridges
• two antigen binding sites

Question 22

describe the function of an antibody (3)

Answer 22

• form an antigen-antibody complex
• ‘clumps’ the antibodies together (agglutination)
• this marks the antigens and helps attract phagocytes to the site of infection

Question 23

what can a vaccine typically contain? (2)

Answer 23

• a dead or weakened form of the pathogen
• a specific antigen or antigens

Question 24

how does the stimulation of memory cells help upon re-infection with the actual pathogen?

Answer 24

• they help coordinate the secondary response
• produces a higher concentration of antibodies AND faster

Question 25

define **herd immunity**

Answer 25

some individuals, despite being unvaccinated, are also protected if the rate of immunisation is high in a population

Question 26

define **antigen-variability**

Answer 26

where some pathogens can vary their antigens to evade detection by immune systems

Question 27

list the **negatives** of vaccines (3)

Answer 27

- they are a drug; may have **side effects** - harms may occur to animals during **animal testing** - even if they show positive effects in animal testing, it doesn't mean they will have the same positive effect in humans

Question 28

define **active immunity**

Answer 28

an individual's own body producing the antibodies and memory cells

Question 29

define **passive immunity**

Answer 29

pre-made antibodies received from elsewhere that are put into the body

Question 30

what procedure can monoclonal antibodies be used in? why are we able to use them in these?

Answer 30

**medical diagnosis** such as pregnancy tests involves attaching a dye/stain - because they can be made in the laboratory as *artificial antibodies*

Question 31

what is the purpose of an **elisa test**?

Answer 31

to detect a specific antigen in a sample through the use of monoclonal antibodies

Question 32

describe the **elisa test** (6)

Answer 32

- **monoclonal antibodies** fixed to the bottom of the well - **sample** (potentially containing an antigen) is added to the well; will bind to the antigen-binding site on the antibody - **well is washed** with water; to remove any unbound antigen - **second monoclonal antibody** is added; attached to an enzyme; also complementary to the antigen - **well is washed again** - substrate is added

Question 33

what is the result of an elisa test if an antigen **is** present within the sample? (2)

Answer 33

- the enzymes will convert the substrate to a different coloured product - this colour change is a positive result

Question 34

what would a **positive control** of the elisa test be?

Answer 34

the sample definitely has the antigen

Question 35

what would be a **negative control** of the elisa test?

Answer 35

the sample definitely does not have the antigen

Question 36

**HIV**: features (4)

Answer 36

- RNA genome - reverse transcriptase; allows production of a copy of DNA from viral RNA - genome is surrounded by a capsid - lipid envelope contains attachment proteins

Question 37

which cells specifically does HIV bind to?

Answer 37

**t helper cells** CD4 receptors

Question 38

describe the process of **HIV replication** (7)

Answer 38

- attachment proteins bind to CD4 receptors on t helper cells - viral RNA and reverse transcriptase enter the cell - reverse transcriptase converts viral RNA into DNA using host nucleotides - viral DNA moves into the nucleus and is inserted into the host cell genome - transcription of HIV DNA into HIV mRNA which is translated to produce HIV proteins - infected t helper cell starts to assemble new virus particles (**virions**) - virus particles are released from the t helper cell

Question 39

“over time, the number of t helper cells _____________ as a result of HIV infection”

Answer 39

decreases

Question 40

how do antibiotics work? (2)

Answer 40

- by preventing bacteria from synthesising murein cell walls or by directly damaging the cell wall - **some** antibiotics also inhibit binary fission by preventing DNA replication and protein synthesis