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29 Cards in this Set
- Front
- Back
Define antigens |
Molecules (usually proteins) which generate an immune response when detected by the body; usually on the surface of cells |
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What does the immune system use antigens to identify? |
Pathogens, abnormal body cells (like cancer), toxins, cells from other individuals |
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Describe the role of the phagocyte |
Phagocytes recognise foreign antigen on a pathogen, forms pseudopodia around it and engulfs it by moving it into the cytoplasm, forms a phagocytic vacuole, a lysosome fuses with this and lysozymes hydrolyse the pathogen. The phagocyte then presents the antigens on its CSM (antigen-presenting cell), and the rest of the debris is expelled via exocytosis |
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Describe how helper T-cells are activated |
The receptor proteins bind to complementary antigens presented by phagocytes, activating the T-cell to stimulate other cells via chemicals. |
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Describe the cellular response |
T-cells and other immune cells they interact with, e.g. the helper T-cell response stimulates phagocytes to engulf foreign cells and activates cytotoxic T-cells which kill foreign cells |
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What is the humoral response? |
B-cells, clinal selection and monoclonal antibodies |
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Explain the role of B-cells in the immune response |
B-cells activate with chemicals from the T-helper cell and when antibodies covering the B-cells binds to a complementary antigen. The B-cells undergo clonal selection to divide into genetically identical plasma cells, which then release many antibodies all complementary to the same specific antigen |
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Describe the structure of antibodies |
They are proteins with 2 identical specific variable regions which form antigen binding sites - very specific to one antigen due to unique tertiary structure that is only complementary to one shape. Have the same constant regions which are bonded by 2 disulfide bridges. Constant region also known as heavy region, variable is light region. Also has hinge proteins. |
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Describe how antibodies deal with antigens |
2 binding sites mean they can bind to 2 pathogens at the same time, which clumps them together (agglutination) and so makes it easier for phagocytes to find and engulf them, leading to the destruction of the pathogen |
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Describe the role of memory B-cells |
B-cells also differentiate into memory B-cells which are activated when the same antigen is encountered again - stimulates a faster secondary response as clinal selection happens faster and the correct T-cells can be immediately activated |
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Explain why the secondary immune response is faster than the primary |
Primary response is slow as not many B-cells around specific to that antigen so have to undergo clonal selection - finding correct helper T-cell also takes time |
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Define a vaccination |
A dead or inactive form of a pathogen containing the antigens to stimulate the immune response without causing active infection to the individual |
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Explain how vaccinations cause immunity |
The antigens trigger the immune response as normal, activating B-cells to make memory cells for the antigen so that if live pathogen infects the secondary immune response is triggered and person does not show symptoms |
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Explain how herd immunity comes abot |
Vaccines reduce the occurrence of the disease so those unvaccinated are less likely to catch the disease as there are fewer people to catch it from |
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How does HIV cause disease? |
HIV kills helper T-cells, and when their level falls beyond a certain point it means that an immune response can not be mounted against foreign antigens, and so body can’t fight off simple infections (developing into AIDS) and person dies from them - e.g. pneumonia |
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How does HIV replicate? |
Attachment proteins bind to receptors on helper T-cell, capsid releases into cell and uncoats to release RNA into cytoplasm, reverse transcriptase makes a complementary strand of DNA from viral RNA template, from this double stranded DNA is made and inserted into human DNA, causes host cell enzymes to make viral proteins which assemble into new viruses and bud from the cell to infect more cells |
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Why may a HIV infected person not show symptoms for a period of time? |
HIV initially replicated rapidly causing flu-like symptoms, then the replication drops during latency period - until activated again person won’t show any symptoms |
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Why don’t antibiotics work against viruses? |
Antibiotics kill bacteria by targeting bacterial enzymes and ribosomes - but viruses do not have those, so use host cell’s - cannot target them as would cause significant damage to the host: |
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How do antiviral drugs work? |
Target virus-specific enzymes, like reverse transcriptase in HIV, and since humans don’t use these it does not affect the host cell. Called reverse-transcriptase inhibitors. |
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How can HIV spread be reduced? |
Educating about risks of unprotected sexual intercourse, injecting bodily fluids and mothers taking antiviral drugs to reduce chance of baby being HIV positive |
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How can pathogens evade the immune system? |
Antigen variability means that the memory cells do not recognise the new form of the antigen, so the slower primary response occurs which means symptoms are shown |
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Define active immunjty |
When the immune system makes its own antibodies when stimulated by an antigen Natural - antigens from catching a disease Artificial - vaccinations |
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Define passive immunity |
When given antibodies made by a different organism Natural - antibodies in breast milk and placenta Artificial - injected with someone else’s antibodies |
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Give advantages of active immunity |
Memory cells are produced, protection is long-term as complementary antibodies already present |
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Describe the advantages of passive immunity |
Doesn’t require exposure to antigen, protection is immediate |
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Define monoclonal antibodies |
Proteins produced by genetically identical B-cells which are all complementary to the same specific antigen - all identical in structure |
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Why are monoclonal antibodies useful in medicine? |
You can make monoclonal antibodies that bind to anything. Can be used to target drugs to particular cells like cancer cells by making them complementary to their antigens and attaching the drug Can target a particular substance for diagnosis, like bind to hCG to show pregnancy |
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Describe how to make an ELISA test |
Bind antigen in well, add sample of blood, if antibodies present (from fighting the disease) then will bind to antigen, well washed out to remove unbound antibodies, secondary antibody with enzyme added to well which binds to primary antibody so of present will bind, well washed out, a solution with substrate to the enzyme added, if enzyme present a colour change will occur to indicate a positive result |
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Describe the HIV structure |
Spherical, has core of RNA genetic material and some proteins (e.g. enzymes like reverse transcriptase), a protein coating called a capsid, extra outer layer called an envelope from stolen membrane of host cell, attachment proteins complementary to helper T-cells |