cell recognition & the immune system Flashcards
pathogen =
microorganism that causes a disease (& immune response)
> eg. virus, bacteria
cell recognition
- every cell has specific molecules on its surface membrane
- can be identified
- self/ non-self cells
antigen =
foreign protein that stimulates an I.R
antibody =
protein specific to an antigen, produced by B cells
struc. of antibody
- quaternary struc (2 polypeptides)
- variable region (comple. to antigen)
- light chain & heavy chain
- hinge region
- disulfide bonds join 2 diff. polypeptides
antigen variability
- mutation of DNA
- altered tertiary struc. of antigen
- it can bind to receptors of other species
- memory cells no longer comple. to antigen
capsid variability
- mutation of RNA
- altered tertiary struc. of viral attachment protein
- it can bind to receptors of other species
types of cells that can stimulate an I.R (immune response)
- pathogens
- cancer/tumour cells
- cells from other organisms/transplants
- self-cells if infected by virus
phagocytes
- large, white blood cells
- engulf & remove dead/invading pathogens
the 2 types of phagocytes
- macrophages
- neutrophils
neutrophils
- rapid reaction force
- lobed nucleus to squeeze through capillaries
process of phagocytosis
1.phagocyte binds to antigen
2.cytoplasm of the phagocyte engulfs the pathogen
3.this forms a phagosome vesicle which fuses with lysosomes
4.lysozymes digest the pathogen
5.antigen from pathogen displayed on cell-membrane
the 2 types of lymphocytes
- T cells
- B cells
T cells
- mature in thymus gland
B cells
- mature in bone marrow
the specific, cell-mediated response
(role of T cells)
1) Helper T cell binds to antigen displayed on the phagocyte
2) Helper T cell releases cytokines
3) cytokines stimulates killer T cells & specific B cell (clonal selection)
the humoural response
(role of B cells)
1) antibody on surface of activated B cell binds to comple. antigen
2) B cell divides by mitosis to make plasma cells
3) plasma cells produce antibodies
4) some plasma cells release monoclonal antibodies
monoclonal antibodies =
antibodies with same tertiary struc, made by identical B cells specific to one antigen
function of monoclonal antibodies
- carries drugs to specific cells
- blocks receptors on cells
vaccine =
injection of antigens from a pathogen which stimulates the production of antibodies
process of vaccination
1) injection of antigens from pathogen
2) describe specific, cellular response
3) describe humoural response
antigen + antibody =
antigen-antibody complex
—> effects of this formation:
* bacterial cells can agglutinate —> destroyed via phagocytosis
* can neutralise toxins
differences between active & passive immunity
1) active involves memory cells, passive doesn’t
2) active involves production of antibody by plasma cells, passive involves antibody introduced into body from outside
3) active = long term —> antibody produced in response to antigen, passive = short term —> antibody broken down
HIV struc
- attachment proteins
- round lipid envelope
- capsid
- RNA
- reverse transcriptase
process of HIV replication
1) attachment proteins attach to receptors on helper T cell
2) RNA enters cell
3) reverse transcriptase converts RNA to DNA
4) viral protein prod. from DNA
5) virus particles assembled & released
effect of HIV on immune system
- HIV destroys helper T cell
- fewer B cells form plasma cells
- less antibodies prod.
- inability to fight off opportunistic infections
why are antibiotics ineffective against viruses?
viruses are inside cells where antibiotics can’t reach
methods of analysing viral DNA
- genetic fingerprinting
- genome sequencing
developing vaccines against viruses
- identify viral proteins from genetic code
- identify potential antigens to use in vaccines
ELISA test
1) first antigen attaches to pathogen
2) wash to remove unattached antibody
3) second antibody w enzyme attached is added
4) second antibody attaches to antigen
5) substrate added —> colour change for positive result
why is a control well used?
- ensures that only the enzyme causes colour change
- all unattached antibodies washed away
role of antibodies in producing +ve result in ELISA test
- 1st antibody binds with immobilised antigen attached to well
- 2nd antibody w attached enzyme is added —> binds w substrate
- colour change occurs
why is the ELISA test specific?
- antibody has tertiary struc.
- comple. to binding site on antigen
