Immunity Flashcards
Antigen definition
• An antigen is a protein/glycoprotein
• that stimulates an immune response/the production of a specific antibody
When a pathogen enters the body it may be destroyed by phagocytosis. Describe how.
- Phagocyte attracted by a substance / recognises (foreign) antigen;
Accept named substance eg chemical / antigen - (Pathogen)engulfed / ingested;
Accept: description
3.Enclosed in vacuole / vesicle / phagosome;
4.(Vacuole) fuses / joins with lysosome;
5.Lysosome contains enzymes;
Accept named example of enzyme
6. Pathogen digested / molecules hydrolysed;
Neutral: Destroved
Specific immune response types
It features two main types of response to pathogens:
⚫ the cellular or cell-mediated response involves highly- specialized cells that target pathogens inside cells.
⚫ the humoral or antibody- mediated response targets pathogens in body fluids with antibodies.
Lymphocytes
• Lymphocytes are a type of white blood cells (leukocyte). They are found in the blood and lymph tissue. They form the specific immune response.
• Lymphocytes recognise antigens and co- ordinate the immune response
There are two types of lymphocyte:
• B lymphocytes – bone marrow • T lymphocytes - thymus
Cytotoxic T cells
• Kill body cells that are infected with by ‘non self’ material
• They kill by making holes in the cell surface membrane using
chemicals called perforins
• These allow water to rush into the cell causing it to burst
• T helper cells
• T helper cells – these cells produce interleukins, a type of cytokine. This stimulate B cell and antibody production, and attracts other T cells and antibodies.
Cell Mediated Response Model Answer
• Antigen is presented on the surface of the phagocyte (antigen presenting cell)
• Helper T cells have a complementary receptor to the antigen being displayed
• When activated by the antigen Helper T cells undergo mitosis
• Producing more T helper cells and cytotoxic T Cells
• Cytotoxic T cells kill infected cells by producing perforins (that make holes in the cell surface membrane)
What do antibodies do
- Antibody-antigen complex
stimulating the digestion by phagocytosis. - Most pathogens cannot affect the bodies cells once they formed an antibody-antigen complex
- Agglutination
• One antibody binds to two pathogens, causing them to clump together
• This makes pathogens more easily engulfed by phagocytosis - Neutralisation
• Antibodies can act as antitoxins, binding with toxins produced by pathogens
• This makes them harmless
Humoral immunity
- T helper cells bind to the antigens on the specific B cell. This is clonal selection as the correct B cell is cloned.
- T helper cells activate other B cells.
- The B cells rapidly divide by mitosis to produce many different B cells (plasma and memory cells). This is clonal expansion.
- These cloned plasma cells produce specific complementary antibodies to the pathogen
What is a monoclonal antibody?
Q1.(a) (Antibodies with the) same tertiary structure
OR
(Antibody produced from) identical/cloned plasma cells/B cells/B lymphocytes;
Give one example of using monoclonal antibodies in a medical treatment.
Targets/binds/carries drug/medicine to specific cells/antigens/receptors
OR
Block antigens/receptors on cells;
Describe the role of antibodies in producing a positive result in an ELISA test.
1.(First) antibody binds/attaches /complementary (in shape) to antigen;
2.(Second) antibody with enzyme attached is added;
3.(Second) antibody attaches to antigen;
Accept (second) antibody attaches to (first) antibody (indirect
ELISA test).
4.(Substrate/solution added) and colour changes;
Only award if enzyme mentioned.
Why is HIV so dangerous
• HIV targets the T-cells of the immune system – it binds to a CD4 receptor on the outside of the cells.
• This means there are fewer immune cells to fight infections • Leading to opportunistic infections and rare forms of cancer
How HIV replicates after entering a human cell
- Once HIV has attached to complimentary proteins (CD4) on the surface of the helper T cell, the virus enters the cell and reverse transcriptase converts the viral RNA into DNA.
- This DNA is joined into the DNA of the host cell.
- When the host cell divides the DNA is used to make copies of HIV RNA.
- The HIV capsid (protein) and enzymes are made by host cell ribosomes.
- Everything is assembled by the host cells RER and Golgi apparatus into new virus particles.
- These are packaged into vesicles and “budding off” occurs (where the viruses are wrapped in membrane.
- Vesicles containing virus are released by exocytosis
Why don’t antibiotics work on viruses?
• Many cell antibiotics work on cell walls – they inhibit the formation of crosslinks in peptidoglycan/murein
• Without a functioning cell wall, they cells are more likely to burst due to osmosis
• Viruses rely on host cells for their metabolism – they have no metabolic mechanisms of their own so antibiotics won’t work on them.
• Viruses don’t have a cell wall.
