3.2.4 The immune system

Question 1

What is a pathogen?

Answer 1

An organism that causes disease

Question 2

What is an antigen?

Answer 2

A molecule that is recognised as non-self which raises an immune response

Question 3

What is an antibody?

Answer 3

A protein with quaternary structure, which is produced by B lymphocytes / plasma cells and they are complementary to an antigen

Question 4

What is non-specific immunity?

Answer 4

They are immediate/ have a rapid response and they respond in the same way regardless of the type of pathogen
e.g. physical / chemical barriers (stomach acid, skin, mucus) / phagocytes

Question 5

What is specific immunity?

Answer 5

They have a slower response and they are dependent on the antigens, found on surface of pathogen
e.g. T lymphocytes, B lymphocytes

Question 6

What are phagocytes?

Answer 6

They are non-specific immune cells that engulf pathogens, then digest them

Question 7

What are T lymphocytes?

Answer 7

They are specific immune cells that mature in the thymus, they are associated with cell-mediated immunity

Question 8

What are B lymphocytes?

Answer 8

They are specific immune cells that mature in the bone marrow, they are associated with humoral immunity - they produce antibodies

Question 9

What are memory cells?

Answer 9

They remain in the body after infection and live much longer than other immune cells. They respond quickly if the same pathogen is encountered again

Question 10

Describe the process of phagocytosis.

Answer 10

1. Phagocyte recognises the foreign antigens on a pathogen
2. Cytoplasm of phagocyte moves around the pathogen, engulfing it
3. Pathogen is now contained in a phagosome (phagocytic vacuole) in the cytoplasm
4. Lysosome fuses with phagosome, forming phagolysosome, lysozymes (hydrolytic enzymes) now fuses towards the pathogen
5. Pathogen is hydrolysed by lysozymes, it now presents the pathogen’s antigens by sticking them on its surface to activate other immune system cells

Question 11

What are lymphocytes activated by?

Answer 11

Antigen-presenting phagocytes, virally infected cells, cancer cells, transplanted cells

Question 12

What happens to Helper T lymphocytes when they meet an antigen-presenting phagocyte.

Answer 12

If they have complementary receptors to antigens, clonal expansion is triggered and they start dividing by mitosis

Question 13

What are the roles of newly divided Helper T lymphocytes.

Answer 13

Activate B lymphocytes

Activate cytotoxic T lymphocytes

Enhance phagocytosis

Become memory T lymphocytes

Question 14

What do cytotoxic T lymphocytes do?

Answer 14

They release perforin which put holes in the pathogen, damaging the integrity of cell membrane, allowing substances to enter and exit - killing pathogen

Question 15

What happen to B lymphocytes when they meet an antigen presenting phagocyte?

Answer 15

If they have complementary antibodies to antigens, they will bind to them, they will then be activated by Helper T lymphocytes, triggering clonal expansion

Question 16

What are the roles of newly divided B lymphocytes?

Answer 16

Most:
Plasma cells - release antibodies

Some:
Memory B lymphocytes

Question 17

Where do T and B lymphocytes mature at?

Answer 17

T: Thymus
B: Bone marrow

Question 18

How are antibodies released from B lymphocytes when faced with pathogen?

Answer 18

1. Pathogens have antigens on its surface
2. Phagocytes present antigens on their surface
3. Helper T lymphocytes with the complementary receptors bonds to the antigens
4. This activates B lymphocytes with the complementary antibodies
5. B lymphocytes divide by mitosis/ go through clonal expansion
6. Some become plasma cells which all releases the same antibodies

Question 19

What are monoclonal antibodies?

Answer 19

Antibodies that are all identical in structure, produced from a single group of genetically identical B cells

Question 20

How many polypeptide chains make up an antibody?

Answer 20

4
2 heavy chains
2 light chains (shorter on the outside)

Question 21

How are the antigen binding-sites of antibodies specific?

Answer 21

Binding sites are located in variable regions on antibodies

Antibodies are proteins - their tertiary structures are unique

Question 22

What bond joins the two heavy chains of antibodies together?

Answer 22

Disulphide bond

Question 23

What is agglutination of antibodies?

Answer 23

As each antibody have 2 binding sites, by binding two different antigens to the same antibody, pathogens are clumped together

Question 24

What is the benefit of agglutination?

Answer 24

More pathogens are clumped closely together, more could be engulfed by phagocytes - enhance phagocytosis

Question 25

What is an ELISA test and what is it used for?

Answer 25

Test for pathogenic infections/allergies/ (anything you can make an antibody for) It shows whether or not the patient has any antibodies to a certain antigen or vice versa.

Question 26

How does an ELISA test work?

Answer 26

1. Blood sample is added to a well with fixed antibodies at the bottom (stir + incubate + wash off) 2. Primary Ab is added and will bind with antigen (if present) (stir + incubate + wash off) 3. Secondary Ab is added and will bind with primary Ab (if present as its complementary) Enzyme which catalyses colour changing reaction is attached to secondary Ab (stir + incubate + wash off) 4. Substrates to enzyme are added , enzyme-substrate complex will form if enzymes are present - colour change

Question 27

Why are secondary Ab used?

Answer 27

To amplify signal and to bring along enzymes attached to it

Question 28

Why is the well washed off between each step?

Answer 28

To get rid of anything that is not bound to something

Question 29

What is targeted therapy?

Answer 29

Drugs that find and attack cancer cells

Question 30

What are the two ways targeted therapies can slow down the growth of cancer cells?

Answer 30

1. Antibodies which are complementary to cancer's unique receptor is bound to a drug Antibody will bring drug to cancer cells - only a small dose is needed as most will bind to cancer cells 2. Antibodies which are complementary to cancer's unique receptor will bind to receptors instead of growth factors Growth factors that tell cells to divide will no longer be able to bind to receptors - blocked

Question 31

What is the similarity between passive and active immunity?

Answer 31

Both could be stimulated naturally and artificially

Question 32

What is active immunity?

Answer 32

The immunity you get when your immune system makes its own antibodies after being stimulated by an antigen

Question 33

What is passive immunity?

Answer 33

The immunity you get from being given antibodies made by a different organism (your immune system doesn't produce any antibodies of its own)

Question 34

What are the differences between passive and active immunity?

Answer 34

P: doesn't require exposure to antigen A: requires exposure to antigen P: gives immediate protection A: takes a while for protection to develop (produce antibodies) P: doesn't produce memory cells A: produce memory cells P: provides short term immunity A: provides long term immunity P: couldn't result in herd immunity A: could result in herd immunity

Question 35

What is passive immunity caused by?

Answer 35

Natural: Baby acquiring antibodies from its mother through breast milk and placenta Artificial: Injection with antibodies

Question 36

What is active immunity caused by?

Answer 36

Natural: Becoming immune after catching a disease Artificial: Becoming immune after given a vaccination

Question 37

What is HIV and what could it cause?

Answer 37

Human immunodeficiency virus Causes AIDS - Acquired immunodeficiency syndrome

Question 38

What does a virus consists of?

Answer 38

Antigens on surface Genetic material (DNA/RNA) inside a capsid - layer of proteins Surrounded by a matrix (inner) and lipid envelope (optional) - phosolipid bilayer

Question 39

What are found specifically in HIV?

Answer 39

Enzyme - reverse transcriptase in capsid RNA as genetic material

Question 40

Why is HIV able to modify DNA of Helper T lymphocytes

Answer 40

They have receptors that are complementary to antigens of HIV - CD4

Question 41

How does HIV replicate inside the cells of organism

Answer 41

1. Helper T lymphocyte binds to HIV 2. Capsid of HIV is released into Helper T lymphocyte, uncoats and releases RNA and RT into cytoplasm 3. Inside cell, RT is used to make a complementary strand of DNA from viral RNA strand 4. Viral DNA is added to cell's DNA found in nucleus 5. Viral DNA now codes for viral proteins and when released from cell, will infect other cells

Question 42

How does HIV kill its host?

Answer 42

As immune system is weakened (Helper T lymphocytes is virally infected), B lymphocytes can't be activated - no antibodies produced - opportunistic/secondary infections will then be able to attack cells and kill the host