cell recognition and the immune system

Question 1

name the two defence mechanisms of the immune system

Answer 1

adaptive and innate immune response

Question 2

describe the features of an innate immune response

Answer 2

• a non-specific response
• immediate response and the same for all pathogens
• includes physical and chemical barriers (skin, eyelashes, stomach acid…)
• includes phagocytosis

Question 3

describe the features of an adaptive immune response

Answer 3

• a specific response
• slower and specific to each pathogen
• includes cell-mediated responses (t-lymphocytes)
• includes humoral responses (b-lymphocytes)

Question 4

what is an antigen

Answer 4

specific molecules (usually proteins as they can have unique tertiary structures) found on the surface of cells or viruses that when registered as non-self by the immune system, they stimulate an immune response producing antibodies

Question 5

give four examples of what the antigens allow the immune system to identify

Answer 5

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

Question 6

describe pathogens (2)

Answer 6

• organisms that cause disease
• have antigens on their surface, identified as foreign

Question 7

describe abnormal cells (2)

Answer 7

• cancerous or pathogen-infected cells
• have abnormal antigens on their surface

Question 8

describe toxins (3)

Answer 8

• poisonous molecules
• produced by bacteria
• a toxin itself is an antigen

Question 9

describe cells from other organisms of the same species (4)

Answer 9

• occur through organ transplant, blood transfusion
• the cells have antigens slightly different to your own
• generate an immune response for the foreign antigens
• A or B foreign antigens generate an immune response in blood transfusions

Question 10

what is a phagocyte

Answer 10

a cell that eats other cells

Question 11

describe the process of phagocytosis (9)

Answer 11

• phagocytes found in blood tissues, attracted to any chemicals or debris released by pathogens or abnormal cells.
• will engage in chemotaxis (chemicals given off by pathogen will stimulate a deliberate forward movement towards the pathogen)
• contains receptor binding points on cell-surface membrane. will attach to chemical or antigen on the pathogens via the receptors
• phagocyte will change shape and move to engulf the pathogen (this is endocytosis, the engulfing of large particles such as bacteria)
• once engulfed, pathogen is contained with a phagosome vesicle
• lysosome (a vesicle) within the phagocyte will fuse with the phagosome and release its contents
• releases lysosome enzyme into phagosome (this is a lytic enzyme that hydrolyses pathogens)
• pathogen is destroyed
• soluble products released (exocytosis) and absorbed and used by phagocyte

Question 12

how do phagocytes become memory cells

Answer 12

after phagocytosis, the antigen is placed on the cell-surface membrane of the phagocyte. it becomes an antigen-presenting cell (a memory cell)

Question 13

define antibodies

Answer 13

proteins that are specific to the antigen and produced by B-cells

Question 14

what is another name for antibodies

Answer 14

immunoglobulins

Question 14

define antibody-antigen complex

Answer 14

where the variable region of an antibody is COMPLAMENTARY to a SPECIFIC antigen molecule

Question 15

what are light chains in the antibody (also applies to heavy chains)

Answer 15

identical polypeptide chains

Question 16

function of disulfide bridges

Answer 16

• they link the polypeptide chains
• stabilise the quaternary structure

Question 17

what is the variable region in the antibody

Answer 17

region where the sequence of R groups is always different at the end of the polypeptide chain (has a unique tertiary structure specific to one type of antigen)

Question 18

what is the constant region in the antibody

Answer 18

area where the sequence of R groups is always the same (they fold into the same shape)

Question 19

what is agglutination

Answer 19

• as antibodies have two binding sites they can clump together pathogens.
• bind to the surface antigens on pathogens to allow for phagocytes to bind to the antibodies and phagocytose many pathogens at once

Question 20

what is opsonisation

Answer 20

antibodies making molecules for destruction

Question 21

what is neutralisation

Answer 21

• antibodies neutralise toxin particles by forming antibody-antigen complexes with the toxins
• (so they cannot enter the host cell)

Question 22

what is inactivation

Answer 22

antibodies prevent viruses from infecting the host cells

Question 23

four roles of antibodies

Answer 23

• agglutination
• neutralisation
• opsonisation
• inactivation

Question 24

Phagocytosis process

Answer 24

• phagocyte (eg macrophage) will detect toxins released by bacteria and engage in chemotaxis using protein receptors in its cell surface membrane
• endocytosis occurs on binding with pathogen
• form phagosome (vesicle) containing pathogen
• lysosomes contain hydrolytic lysozymes
• fuse to form phagolysosome
• digest by hydrolysis
• release contents by exocytosis