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
contrast and compare active and passive immunity
- active immunity is stimulated by an antigen leading to the production of antibody by plasma cells, whereas passive immunity introduces antibodies from outside the body
- active immunity is slower than passive immunity
- active immunity is a long term solution as memory B cells are produced, but passive immunity act as a short term fix as no memory b cells are produced and the antibodies are broken down.
describe antigenic variability
- due to mutations in the DNA, the cold and flu viruses keep changing the tertiary structure of their antigens
- antibodies from the specific memory cells are no longer complimentary to the antigen
- each new infection causes a new primary response requiring clonal selection and production of the antibody again.
what are monoclonal antibodies
produced from identical/ cloned plasma cells and have the same tertiery structure so therefore the same specific binding site/ variable region which binds to the same antigen
explain how monoclonal antibodies can be used to kill cancer cells
- monoclonal antibodies can be made to have specific shaped variable regions
- which are complementary to bind specific antigens on the cancer cell
- the antibdy is linked to a toxin which kills the cancer cell
why do monoclonal antibodies have minimal sideeffects in cancer treatment
the antigen found on cancer cells is not found on healthy cells and therefore the antibody will not bind the healthy cells and kill them
how can monoclonal antibodies be used in diagnosis of disease
- monoclonal antibodies are complementary for the antigens on cancer cells can be used in cancer diagnosis on biopsy tissue samples.
- the antibody complementary for the cancer antigen has a flourescent tag on it whihch shows up on a microscope
explain how monoclonal antibodies can be used in diagnosis for pregnancy tests
- hCG is only found in urine of pregnant women
- the test strip on the pregnancy tests contain an anti-hCG monoclonal antibody with a coloured dye attached
- urine flows along the test strip and any hCG in the urine binds the monoclonal antibody
- the hCG-antibody complexes then flow into the test area concentrating the dye. this causes the coloured band to appear
- if there us no hCG present then the free floating anti-hCG antibodies just flow past the fixed anti-hCG antibodies and there is no build up of dye so no colour appears
define attachment protein
attaches virus to complementary receptor on host t-cell
define RNA
genetic material of a virus
define reverse transcriptase
enzyme which converts RNA to DNA in host cell
define capsid
outer coat made of protein
define lipid envelope
further outer kayer made of membrane taken from previous host cell
draw and label the sturcture of HIV
describe the process of HIV replication
- attachement protein on HIV binds to a complementary receptor on the helper T-cell
- the capsid enters the cell and releases the RNA into the cytoplasm
- reverse transcriptase makes DNA from the viral RNA
- using the host cells enzymes and ribosomes for protein synthesis, viral proteins are made form the DNA
- new viruses are formed from the proteins which bud from the cell and infect more helper T-cells
what is AIDS
aquired immune deficiency syndrome
how does HIV cause AIDS
- HIV kills helper T-cells
- when the helper T-cell numbers drop very low the immune system starts to fail and serious infections can kill the patient
- AIDS is clinically diagnosed when the helper T-cell number drops below 200 per ml of blood
why do antibiotics not kill viruses
antibiotics can only kill bacteria not viruses
why do antibiotics only kill bacteria
as they target parts of a bacteria whihc are not found in a virus i.e. the bacterial cell wall
why are viruses very difficult to kill
they replicate inside cells and have very few drug targets such as enzymes as thye use host cells enzymes and organelles for replicaiton
what is the target for antiviral drugs
viral reverse transcriptase
why do antivirals not work on every virus
the virus must be a retrovirus which contains reverse transcriptase
