Cells (Cell Recognition and Immune Response) Flashcards
what are antigens?
antigens are usually proteins or glycoproteins in or on the plasma membrane which stimulate an immune response as they are identified as self or non-self
describe how phagocytosis leads to an antigen presenting cell.
-a pathogen enters the body
-the phagocyte detects the pathogen due to it’s foreign antigens.
-the phagocyte’s cytoplasm moves around the pathogen, engulfing it and packaging it into a phagocytic vacuole in the cytoplasm to form a phagosome
-lysosomes then fuse to the vacuole and release hydrolytic enzymes called lysozymes which hydrolyse the pathogen
-the phagocyte absorbs or releases the content from the pathogen hydrolysis
-the phagocyte displays the antigen from the pathogen on its cell surface
outline the cell-mediated response to infection.
-Helper T cells are activated when their receptors on their cell surface membrane bind to complimentary antigens on an antigen presenting cell or pathogen- this is called clonal selection
-once activated this causes the helper T cell to divide rapidly by mitosis, known as clonal expansion.
-they divide into helper T cell, cytotoxic T cells and memory cells. different types of T cells respond in different ways
-when activated the cytotoxic T cells kill abnormal and foreign cells through secreting the enzyme perforin
-when activated the helper T cells release cytokines that stimulate B lymphocytes to divide and develop into antibody-secreting plasma cells.
-the memory cells remain the in the body in case reinfection occurs in which they will divide into helper T cell or cytotoxic T cells
outline the humoral response to infection
-B cells are activated when the antibody molecules on their cell surface membrane bind to a complimentary shaped antigen and when the helper T cells release cytokines.
- once they are activated, the B cells divide rapidly by mitosis in clonal expansion
- plasma cells are produced which produce and secrete antibodies which have a complimentary shape to the antigens
- some b cells develop in to memory cells remain in the bloodstream in low levels in case reinfection occurs. if the antigen is later detected again, these cells will divide into plasma cells
what is an antibody?
proteins secreted by plasma cells
describe the structure of antibody.
-it has a quaternary structure as it has 4 polypeptide chains, two light chains and two heavy chains which are joined together by disulphide bridges
-binding sites on the variable region have a specific tertiary structure which is complementary to an antigen.
how to antibodies lead to the destruction of pathogens?
antibody binds to the antigens on a pathogen which forms an antigen-antibody complex. an antibody has two biding sites so can bind to two pathogens at the same time. this causes agglutination which is when many pathogens are bound together. this enhances phagocytosis as phagocytes can bind to the antibodies and phagocytose many pathogens at once.
how is the primary and secondary immune response different?
-a secondary immune response is a much faster and stronger response than the primary response
-this is because memory cells are produced during the primary response which are able to recognise the foreign antigen when it is encountered again upon reinfection
-during reinfection memory B cells can rapidly divide to form plasma cells which secrete the antibody complimentary to the pathogen. the memory T cells rapidly divide into the right type of T cells to kill the cell
what is passive immunity?
-type of immunity produced by the introduction of antibodies from an external source
-immunity is acquired immediately
-no memory cells produced and antibodies aren’t replaced meaning no lasting immunity
-artificial passive immunity is if you have been injected with antibodies from another organism
-natural passive immunity is if you have received antibodies through mother’s placenta or breast milk
what is active immunity?
-type of immunity produced when an individual’s immune system produces its own antibodies after being stimulated by an antigen
-immunity takes time to develop so isn’t immediate
-provides long lasting immunity as memory cells are produced
-artificial active immunity is if you have received a vaccinations
-natural active immunity is if you have the disease before
explain the principles of vaccination.
-vaccines contain antigens from dead/weakened pathogens
-when injected memory cells are made
-on second exposure the memory cells become active and rapidly produce antibodies in higher quantities
-the antibodies destroy pathogens
define herd immunity
involves vaccination of a large proportion of the population so to reduce carriers of the pathogen making it more unlikely the disease spreads
describe how antigen variability makes it difficult to make vaccines
–the structure and shape of antigens of a pathogen develop variation due to random mutations in the genetic code of the pathogen
-if the pathogens with the new antigens multiply and spread the new strains of pathogen can emerge through natural selection
-these new strains will need different antibodies to be produced during an immune response as the old antibodies will not be complimentary to the new antigens
describe the structure of HIV
-protein layer called the capsid encloses a core that contains two strands of RNA and reverse transcriptase enzymes
-it is surrounded by a lipid envelope which has attachment proteins embedded which help HIV attach to the host helper T cell
how does HIV replicate
- HIV enters the bloodstream
-the attachment proteins attach to the CD4 receptor molecule on the cell membrane of the host helper T-cell
-protein capsid fuses with cell-surface membrane and the viral RNA and enzymes of HIV are released into the cell’s cytoplasm
-inside the cell, the reverse transcriptase converts RNA to DNA
-the viral DNA is transported into the nucleus and the enzyme called integrase fuses it with the host cells normal DNA
-the viral DNA is transcribed into mRNA which uses ribosomes to make viral proteins
-HIV buds of from the helper T cell with a piece of the cells surface membrane surrounding them which forms the lipid envelope
