Please enable JavaScript.
Coggle requires JavaScript to display documents.
2.4 cell recognition and the immune system - Coggle Diagram
2.4 cell recognition and the immune system
lesson 1: phagocytosis
leukocytes use antigens to recognise pathogens or cells from other organisms of the same species e.g cells from transplanted organs
antigens
molecule that triggers an immune response, made from proteins, found either on the surface of pathogens, free in the blood, the surface of infected cells and cancer cells
defence mechanisms
non specific - response is immediate and the same for all pathogens
physical barriers e.g skin
phagocytosis
specific - response is slower and specific to each pathogen
cell mediated response - t lymphocytes
humoural response - b lymphocytes
phagocytosis process
chemicals released by the pathogen or infected body cells (response to chemical stimuli known as chemotaxis)
receptors on surface of the phagocyte attach to the antigen on the pathogen
pathogen is engulfed during endocytosis forming a vesicle called a phagosome
lysosomes containing lysozymes move towards the pathogen/phagosome and then fuses with the phagosome to form a phagolysosome which releases the lysozymes which then hydrolyse the pathogen
useful products of digestion diffuse into the cytoplasm and indigestible material discharged from the cell via exocytosis
sometimes the antigens are displayed on the surface of the phagocyte to trigger an immune response
lesson 2: the humoral response
a specific response and is called the humoral response as it involves antibodies found in the humours e.g blood plasma
carried out by b lymphocytes (plasma and memory cells) which are made in and mature in the bone marrow
process
invading pathogen taken up by b lymphocyte
b lymphocytes process the antigen and present them on their surface
activated helper t cells attach to processed antigen on the surface of the b lymphocytes which causes them to become activated
the activated b lymphocytes divide by mitosis to either
become plasma cells which produce and secrete the antibody specific to to the antigen on the pathogens surface, the antibody destroys the pathogen (primary response)
develop into memory cells, these can respond to future infections by the same pathogen by rapidly dividing and developing into plasma cells that produce specific antibodies (secondary response)
agglutination
the clumping of pathogens, each antibody contains 2 antigen binding sites so can bind 2 at once, this makes it easier for phagocytes to locate and engulf pathogens
lesson 3: cell mediated response
specific response carried out by t cells which respond to antigens on the surface of cells such as infected body cells, phagocytes presenting antigens, foreign body cells or cancerous cells
t helper cells- made in the bone marrow and mature in thymus gland
process
pathogens invade body cells or are taken in by phagocytes
phagocyte places antigens from pathogen on its cell surface membrane
receptors on specific helper t cells bind to antigens
this causes the helper t cell to become activated and begin dividing rapidly by mitosis
the cloned t helper cells either
develop into memory cells that circulate the blood and tissue fluid and enable a rapid response to future infection by the same pathogen
stimulate phagocytes to engulf pathogens
stimulate b lymphocytes to divide
activate cytotoxic t cells to kill infected cells by making holes in their cell surface membranes
cytotoxic t cells
destroy abnormal or infected cells
release a protein called perforin which embedded into the cell membrane causes a pore making the membrane freely permeable resulting in cell death
common for viruses as they replicate within body cells
lesson 4: antibodies
produced by plasma cells - clones from b lymphocytes
variable region - contains the antigen binding sites, each site made from polypeptide chain- shape is dependent on sequence of amino acids, specific sequence results in specific tertiary structure making the binding site complementary to a specific antigen
constant region - region consists of two heavy polypeptide chains and two light polypeptide chains this allows the antibodies to attach to receptors and or cells such as macrophages
hinge region - occurs in the heavy polypeptide chains, allows the antibody to be flexible and enables it to attach to more than one antigen
lesson 5: monoclonal antibodies
produced from a single clone of a b lymphocyte and bind to a specific type of antigen
uses
medical diagnosis
pregnancy tests
positive result
at the reaction site hCG binds to the complementary monoclonal antibodies (which are also bound to dye enzyme) and they are then carried to the test site with the flow of urine
antibodies bound to hCG then bind to a second antibody (which is also bound to a dye substrate) and a chemical reaction occurs and the dye substrate is hydrolysed producing a coloured stripe in the test site
at the control site unbound antibodies bind to a third antibody which has a specific complementary binding site to the antibodies from the reaction site (is also bound to a dye substrate) the dye substrate is again hydrolysed and a second coloured stripe is produced
ELISA - enzyme linked immunoabsorbant assay, used to test for a specific protein and its concentration. used to test for TB, HIV etc
procedure
apply the sample being tested e.g blood to a surface to which the antigens in the sample will attach
wash to remove any unbound antigens
add a second complementary antibody that is attached to an enzyme. this binds to the first antibody if its present
add the antibody that is specific to the antigen that the test is trying to detect, antibodies will bind to antigen if present
wash to remove excess antibodies
add colourless substrate complementary to the enzyme, if enzyme is present it hydrolyses the substrate releasing a colour
amount/concentration of antigen present depends on intrnsity of the colour
wash to remove any unbound antibodies
targeted medication - treat cancerous cells
targeted delivery of drugs to specific cell by attaching the drug to a monoclonal antibody, chemical in the drug will only act upon cells that have the complementary antigen
advantages - only small amount of drug/chemical needed, non targeted cells are unaffected
lesson 6: vaccination
vaccines contain non self antigens which are either attached to attenuated or dead microorganisms or are isolated antigens produced from a microorganism and then purified
when a vaccine is given active immunity is acquired
vaccine contains non self antigen usually attenuated or dead
antigen is engulfed by a phagocyte and the antigen is then presented on the cell surface membrane
t helper cell with a complementary receptor binds to the antigen
t helper cell stimulates b cell with complementary antibodies
b cell clones and differentiates
plasma b cells release large number of antibodies
memory cells remain in the bloodstream
acquired immunity
active immunity- develops a response to an infection or vaccination
natural - antibodies developed in response to an infection
artificial - antibodies developed in response to vaccination
passive immunity - develops after you receive antibodies from someone or somewhere else
natural - antibodies received from mother e.g through breast milk
artificial - antibodies received from medicine
longevity of immunity
passive immunity
short lived - only getting antibodies not plasma b cells and antibodies are gradually broken down, no memory cells produced and antibodies are not replaced
active immunity
longer lived - memory cells are produced in response to antigen, memory cells remain in circulation, memory cells release antibodies rapidly
differences between active and passive immunity
active immunity involved memory cells and passive immunity doesnt
active immunity involves exposure to an antigen whereas passive does not
passive immunity is faster acting as no clonal selection of b lymphocytes
herd immunity
large proportion of the population is immune to a pathogen and the transmission of pathogen is reduced. protects everyone especially those who cannot be vaccinated
advantages of vaccines
can help achieve herd immunity
protect vulnerable members of the community such as the elderly or cancer patients
saves lives
disadvantages of vaccines
potential unpleasant side effects
religious dilemmas
expensive
lesson 7: viruses & HIV
viruses are acellular non living particles which don't have a nucleus cannot survive without a host cell and replicate inside host cells
attachment proteins: bind to cell surface membrane of host cell
genetic material (RNA or DNA) codes for virus proteins
capsid: protein coat
HIV: kills/ destroys helper t cells
HIV infection//replication
attachment proteins in lipid envelope bind to CD4 receptors on surface of T helper cell
lipid envelope fuses with cell surface membrane. HIV RNA and reverse transcriptase enter t helper cell
reverse transcriptase makes DNA copy of viral RNA
HIV DNA moves into nucleus and inserts into the host cells DNA
latency period
transcription of HIV DNA into HIV RNA . translation of HIV RNA into HIV proteins at the ribosomes
HIV RNA a d proteins self assemble into HIV particles
HIV particles leave the cells by budding
how HIV causes AIDS
infection of HIV leads to death of T helper cells
less t helper cells leads to less activation of B lymphocytes, cytotoxic t cells and phagocytes which leads to a compromised immune system
if untreated patients die from other infections such as pneumonia
