paper 1: Cell Recognition and the Immune System Flashcards
define a pathogen
an organism which causes disease
how do pathogens cause disease
by destroying tissues/ cells by breaking down membranes
, by producing toxins
define non-specific defence mechanisms
the response is immediate and is the same for all pathogens
what’s the first line of defence for non specific defence mechanisms
physical barrier: skin, HCl in stomach, epithelial mucus
what is the second line of defence for non specific defence mechanisms
phagocytosis: white blood cells engulf and digest pathogens
define specific defence mechanisms
the response is slower and specific to each pathogen
describe the third line of defence mechanisms
cellular response: t-lymphocytes
humoral response: b-lymphocytes
define an antigen
a foreign molecule with a specific 3D structure found on the surface of cells which stimulate an immune response.
what do antigens enable the immune system to identify
- pathogens
- cells from other organsims of the same species
- toxins
- abnormal body cells
describe the stages of phagocytosis
- a phagocyte recognises foreign antigens on a pathogens
- the phagocyte engulfs the pathogen, forming a vesicle called a phagosome
- lysosomes fuse with the phagosome. Lysozymes are released which hydrolyse molecules of the pathogen to destroy it
- the antigens of the pathogen are presented on the cell surface membrane of the phagocyte. the phagocyte can now be called an antigen-presenting cell.
what are lymphocytes
white blood cells which carry out a specific immune response
describe the cellular response
- an antigen on the cell surface membrane of an antigen presenting phagocyte binds to a contemporary receptor on a specific Helper T cell.
- This specific Helper T cell then stimulates
- more phagocytes
- specific B cells
- cytotoxic t cell (to kill infected cells)
describe the humoral response
- specific B cells are activated by specific helper t cells
- B cell clone into plasma cells and memory B cells
- plasma cells secrete many identical monoclonal antibodies
- antibodies bind to complimentary antigen and agglutinate pathogens
what is agglutination
- antibodies bind to 2 antigens and different pathogens causing them to clump together and be held in one area
- this makes the pathogens more easily engulfed and hydrolysed by phagocytes
how do memory B cells work
- when re-infected with the same antigen
- specific memory B cells with the complimentary antibody divide by mitosis
- to form plasma cells
- which make more antibodies much more quickly
what is clonal selection
where only the B cell with the specific antibody complimentary to the antigen is cloned
what is an antibody
a protein specific to an antigen, secreted by plasma cells
draw and label the structure of an antibody
describe the structure of an antibody
- antibodies are made of 4 polypeptide chains- 2 light and 2 heavy joined by disulfide bridges
- the constant region is the same in all antibodies
- the variable region differs between antibodies from different plasma cells
- each antibody has a specific tertiary structure with a specific variable region
- which is complimentary and binds to only one type of antigen
- an antibody bound to an antigen is called an antibody- antigen complex
how does the structure of an antibody allow agglutination
antibodies have 2 binding sites so they can bind 2 antigens on different pathogens at the same time
describe the primary immune response
the primary response is when the antigen infects the body for the first time and is slower than the secondary response as it takes time for specific B cells to clone into plasma cells. Therefore antibodies are produced slower
describe the secondary immune response
the secondary response is when the same antigen re-infects the body. This response is bigger and faster because the memory b cells with complimentary antibody clone much faster into plasma cells. These plasma cells produce many more antibodies much quicker so no symptoms occur.
describe ad explain how vaccinations work
- vaccines contain antigens of a pathogen
- phagocyte presents the antigen on cell surface membrane
- specific helper t cells activate specific b cells
- b cells clone into plasma cells and memory b cells
- plasma cells make antibodies which bind to the antigen and cause its destruction
- when re-infected with the same antigen, specific memory b cells with complimentary antibodies to the antigen recognise the antigen immediately. they then clone into plasma cells. these plasma cells produce many more antibodies much more quickly.
describe herd immunity
if most people are vaccinated against a disease this provides protection for the whole population. those who aren’t vaccinated are still protected because they are less likely to come into contact with infected individuals
