topic 2 - the immune system

Question 1

what triggers an immune response

Answer 1

foreign antigens

Question 2

what are antigens

Answer 2

marker molecules (usually proteins) present on the surface of cells that can generate an immune response when detected by the body

Question 3

what are antigens used by the immune system to identify

Answer 3

(1) pathogens
(2) abnormal body cells
(3) toxins/ cells from other individuals of the same species

Question 4

what are the four main stages in the immune response

Answer 4

(1) phagocytes engulf pathogens
(2) phagocytes activate t-cells
(3) t-cells activate b-cells, which divide into plasma cells
(4) plasma cells make more antibodies to a specific antigen

Question 5

what is a phagocyte

Answer 5

a type of blood cell that carries out phagocytosis

Question 6

what is phagocytosis

Answer 6

the process by which a cell uses its plasma membrane to engulf pathogens

Question 7

where are phagocytes found

Answer 7

in the blood and in tissues and are the first cells to respond to an immune system trigger inside the body

Question 8

what’s an example of a phagocyte

Answer 8

macrophage

Question 9

what is the first step to a phagocyte engulfing a pathogen

Answer 9

a phagocyte recognises the foreign antigens on a pathogen

Question 10

what is the second step to a phagocyte engulfing a pathogen

Answer 10

the cytoplasm of the phagocyte moves round the pathogen, engulfing it

Question 11

what is the third step to a phagocyte engulfing a pathogen

Answer 11

the pathogen is now contained in a phagocytic vacuole (a bubble) in the cytoplasm of the phagocyte

Question 12

what is the fourth step to a phagocyte engulfing a pathogen

Answer 12

a lysosome (an organelle that contain enzymes called lysozymes) fuses with the phagocytic vacuole - the lysozymes break down the pathogen

Question 13

what is the fifth step to a phagocyte engulfing a pathogen

Answer 13

the phagocyte then presents the pathogen’s antigens - it sticks the antigens on its surface to activate other immune system cells

Question 14

what is a t-cell

Answer 14

otherwise known as a t-lymphocyte is a type of white blood cell

Question 15

what activates the t-cell

Answer 15

when its receptor proteins on its surface bind to complementary antigens presented to it by pathogens

Question 16

different t-cells respond in different ways, give an example

Answer 16

helper t-cells (tH cells) release chemical signals that activate and stimulate phagocytes and cytotoxic t-cells (tc cells), which kill abnormal and foreign cells

Question 17

what are the two main types of t-cells

Answer 17

(1) cytotoxic t-cells which destroy infected cells
(2) helper t-cells which send signals that direct other immune cells to fight infection

Question 18

what is a b-cell

Answer 18

otherwise known as b-lymphocytes is a type of white blood cell that is covered in antibodies which originates and matures in bone marrow

Question 19

why do different b-cells bind to different shaped antigens

Answer 19

because each b-cell has a different shaped antibody on its membrane

Question 20

what are the three steps to how b-cells divide into plasma cells

Answer 20

(1) when the antibody on the surface of a b-cell meets a complementary shaped antigen, it binds to it
(2) this, together with substances released from helper t-cells, activates the b-cell - this process is called clonal selection
(3) the activated b-cell divides into plasma cells

Question 21

what other cell is identical to b-cells

Answer 21

plasma cells

Question 22

what are monoclonal antibodies

Answer 22

antibodies specific to the antigen which are secreted by a single clone of a specific white blood cell (plasma cells)

Question 23

what do monoclonal antibodies bind to, what does this form

Answer 23

they bind to antigens on the surface of the pathogen to form lots of antigen-antibody complexes

Question 24

name seven structures on the antigen-antibody complex

Answer 24

(1) antigen
(2) variable regions
(3) hinge protein
(4) constant regions
(5) light chain
(6) disulfide bridges
(7) heavy chain

Question 25

why do antibodies have two binding sites

Answer 25

so they can bind two pathogens at the same time - meaning that pathogens become clumped together (this is called agglutination)

Answer 26

phagocytes then bind to the antibodies and phagocytose many pathogens at once - this process leads to the destruction of pathogens carrying this antigen in the body

Question 27

what are antibodies

Answer 27

proteins produced by the immune system in response to foreign substances - they are made up of chains of amino acids

Question 28

what does the specificity of an antibody depend on

Answer 28

its variable regions - which form the antigen binding sites

Question 29

what structure of an antibody is unique

Answer 29

its variable region with a unique tertiary structure (due to different amino acid sequences) that’s complementary to a specific antigen

Question 30

what does the immune response split into

Answer 30

cellular and humoral

Question 31

what is the cellular immune response

Answer 31

the t-cells and other immune system cells that interact with

Question 32

what is the humoral immune response

Answer 32

b-cells, clonal selection and the production of monoclonal antibodies form the humoral response

Question 33

what’s another word for an antibody

Answer 33

immunoglobulin

Question 34

what is the primary response

Answer 34

when an antigen enters the body for the first time and activates the immune system

Question 35

why is the primary response slow

Answer 35

because there aren’t many b-cells that can makes the antibody needed to bind to it

Question 36

what do t-cells and b-cells produce after being exposed to an antigen, what do they do

Answer 36

memory cells - these memory cells remain in the body for a long time - memory t-cells remember the specific antigen and will recognise it a second time round - memory b-cells record the specific antibodies needed to bind the antigen

Question 37

what is the secondary response

Answer 37

the second time the body is infected with the same pathogen, the immune system will produce a quicker, stronger immune response

Question 38

how do b-cells and t-cells perform clonal selection in the secondary response

Answer 38

memory b-cells are activated to divide into plasma cells that produce the right antibody to the antigen - memory t-cells are activated and divide into the correct type of t-cells to kill the cell carrying the antigen - clonal selection is faster in this stage