Immunity

Question 1

What is the other name for antibodies?

Answer 1

immunoglobulins

Question 2

Antibody structure

Answer 2

Y shaped glycoproteins

• two identical polypeptide chains called ‘the heavy chains’
• two shorter ‘light chains’
• chains held together by disulphide bridges

Question 3

variable region

Answer 3

binding site of about 110 amino acids on the heavy and light chains.

Specific as different on every antibody

Question 4

contstant region

Answer 4

bit of an antibody that doesn’t change ie. not the variable region (binding site)

Question 5

opsonin

Answer 5

chemicals that bind to pathogens and tag them so they can be more easily recognised by phagocytes

• antigen-antibody complex acts as opsonin

Question 6

agglutinins

Answer 6

antibodies act as agglutinins, causing pathogens with attached antigen-antibody complexes to clump together

-> helps prevent pathogens spreading throughout the body and makes it easier for phagocytes to engulf a number of pathogens at one time

Question 7

anti-toxins

Answer 7

antibodies act as anti-toxins, binding to the toxins made by pathogens and making them harmless

Question 8

b lymphocytes mature in the

Answer 8

bone marrow

Question 9

t lymphocytes mature in the

Answer 9

thymus gland

Question 10

what are the 4 types of T lymphocyte?

Answer 10

T helper cells
T killer cells
T regulator cells
T memory cells

Question 11

what are the 3 types of B lymphocyte?

Answer 11

Plasma cells
B effector cells
B memory cells

Question 12

interleukins

Answer 12

produced by T helper cells.
- type of cytokine (cell signalling molecule)
- stimulate the activity of the B cells, which
=== increase antibody production
=== stimulate the production of other types of T cells
=== attract and stimulate macrophages to ingest pathogens with antigen-antibody complexes

Question 13

perforin

Answer 13

produced by T killer cells

- kills pathogen by making holes in the cell membrane so that it is freely permeable

Question 14

T killer cells

Answer 14

destroy pathogen carrying antigen
- produce a chemical called perforin, which kills pathogen by making holes in the cell membrane so that it is freely permeable

Question 15

T helper cells

Answer 15

• have CD4 receptors on their csm which bind to surface antigens on APCs.
• produce interleukins, which stimulate the activity of the B cells

Question 16

T memory cells

Answer 16

live for long time

• part of immunological memory
• if they meet the same antigen again, they rapidly divide and form clones of T killer cells that destroy the pathogen

Question 17

T regulator cells

Answer 17

• supress the immune system
• stop the immune response once a pathogen has been eliminated
• ensures body recognises self antigens and does not stimulate an autoimmune response

Question 18

Plasma cells

Answer 18

• produce antibodies for a particular type of antigen and release them
• only lives for a few days but v active

Question 19

B effector cells

Answer 19

divide to form plasma cell clones

Question 20

B memory cells

Answer 20

• long life span
• ## immunological memory

Question 21

What do MHC proteins do?

Answer 21

bind to the antigen fragments after a pathogen has been digested by a macrophage and displays the antigens on the csm, making the macrophage an APC

Question 22

Outline how the structure of an antibody molecule is related to its function. (3)

Answer 22

variable region is antigen binding site; R receptors / ‘sticky ends’ / active site

(shape of) variable region specific to antigen / amino acid sequence (of variable region) gives, complementary / matching, shape;

hinge region allows flexibility in binding / AW;

constant region, for binding to receptors on cells / phagocytes / mast cells;

AVP; e.g. disulphide bonds hold polypeptide chains together

Question 23

Suggest why the base sequence in the genes for human antibodies is more similar to that found in a chimp than to that found in a mouse. (2)

Answer 23

human and chimp are more closely related;
common ancestor is more recent;
less time for, mutations / variation, to arise;

Question 24

Name the type of cell that produces antibodies. (1)

Answer 24

plasma/effector cell

Question 25

State one function for the constant region in an antibody

Answer 25

attach/bind to (receptors on) phagocyte;

Question 26

State one function for the binding site in an antibody

Answer 26

bind/attach to antigen;

Question 27

State one function for the disulphide bridge in an antibody

Answer 27

hold, shape/tertiary structure, of molecule; hold (polypeptide) chains together/maintain quaternary structure;

Question 28

State one function for the hinge region in an antibody

Answer 28

allow molecule to, bend/flex/bind with more than one pathogen;

Question 29

Explain why the part of the antibody molecule incorporating the binding site is often called the variable region. (2)

Answer 29

different antibodies:

have different amino acid sequence;
have different shape;
fit different antigens;
ref. to specificity/complementary; A lock and key

Question 30

During an immune response, phagocytic cells are attracted to the site of infection.

Describe the action of these phagocytic cells at the site of infection. (4)

Answer 30

pathogen / bacterium, recognised as foreign;
antigens / pathogen is antigenic;
engulfed / phagocytosis / phagocytosis described / endocytosis;
in, vesicle / phagosome / vacuole;
lysosomes fuse to vesicle;
release, lysins / enzymes / named enzyme;
digest / break down, pathogen / bacterium;

Question 31

Explain why there is a delay between the first infection by the pathogen and the appearance of antibodies in the blood. (2)

Answer 31

time taken for:
antigen presentation; 
clonal selection; 
clonal expansion; 
differentiation (of B cell into plasma cell);
production of antibodies; 

there are no memory cells;

Question 32

Describe how antibodies act on invading pathogens, such as bacteria or viruses. (2)

Answer 32

• variable region binds to, antigen / pathogen;
• antigen-binding site variable region specific to, antigen / pathogen;
• antigen-binding site agglutinate pathogens / stick pathogens together;
• immobilise pathogens / attach to flagellum (of pathogen);
• combine with pathogen to stop entry to cell;
• break wall of bacterium open / lysis;
• constant region, attracts phagocytes / makes it easier to engulf bacterium;

Question 33

In October 2004, scientists announced successful trials of a malaria vaccine. The vaccine was developed from proteins taken from the parasite, ………………………………..
falciparum. When the proteins enter the body they act as ……………………………….. which are recognised as foreign by the immune system. These foreign proteins activate lymphocytes called T cells which then divide to increase in numbers. Some of these newly cloned cells become ……………………………….. cells which attack infected cells in the liver. Others become ……………………………….. cells which release a hormone-like messenger molecule called a ……………………………….. . These molecules activate B
cells to divide and produce plasma cells. The B cells also produce ……………………………….. cells that stay in the body for a number of years. The result is an immune system prepared to make a strong attack on the parasite when it enters the body.

Answer 33

Plasmodium;
antigens; 
cytotoxic / killer / T killer / Tk / Tc;
 helper / T helper / Th; 
cytokine / lymphokine; 
memory;

Question 34

Name the molecules, released by plasma cells, that attack the parasite when it enters the body. (1)

Answer 34

antibodies/ immunoglobulins

Question 35

Suggest why it has been difficult to produce a malaria vaccine. (3)

Answer 35

1 several, strains / species, of malarial parasite;

2 parasite is a, protist / protoctist / eukaryote;

3 many surface, proteins / antigens;

4 mutation;

5 ref to antigenic drift / antigens may change;

6 ref to antigenic shift;

7 much of life cycle inside, host cells / red blood cells / hepatocytes;

8 hidden / protected, from immune system; A ref to antigen concealment

Question 36

What is meant by the word artificial in the term artificial active immunity? (1)

Answer 36

(antigens) injected / taken orally; ora (‘not caught’)