Immune System Flashcards
What is an antigen?
A PROTEIN in the cell-surface membrane that triggers an IMMUNE RESPONSE.
Describe the process of how phagocytes destroy pathogens?
1) Pathogen releases chemicals called chemoattractants which attract phagocytes which moves along the concentration gradient
2) The pathogen is ENGULFED in a vesicle called a PHAGOSOME
3) The phagosome membrane FUSES with the membrane of the lysosomes in the phagocyte
4) Lysosome contains hydrolytic enzymes, lysozymes which are released into phagosome
5) Lysozymes hydrolyse the molecules the pathogen is made of
6) Soluble products of breakdown are absorbed into cytoplasm (e.g. glucose, amino acids, antigens)
7) Non-soluble products expelled out of the cell
What is a chemoattractant? Where is it produced?
Chemical that attracts pathogens
In the pathogen itself, or the cells affected by pathogens.
What is an example of a chemoattractant?
Cytokines
What are phagocytes?
Cells which engulf pathogens, or cells that are infected, damaged, or dying.
What do phagocytes include?
Macrophages
Dendritic cells
What are antigen presenting cells (APC)?
Cells that have engulfed a pathogen and presented it’s antigens on the surface membrane.
How are T cells activated?
When the receptor cells bind to complementary antigens on the surface of phagocytes that have presented them.
Outline the process of the cell-mediated response [6 marks]
1) Phagocyte engulfs pathogen - presents antigens on cell surface membrane = APC
2) Specific Helper T-cells with RECEPTORS complementary to the specific antigen BIND to the APC. The TH cells become ACTIVATED
3) The activated TH cells divide by mitosis (clonal selection)
> They also secrete chemicals which activate other T-cells and B-cells which have the same receptors.
> T helper cells divide by mitosis. T helper cells…
4)
> Activates Killer T cells / Cytotoxic T-Cells (TC) are stimulated –> Produces chemicals which make the APC’s membrane permeable - the holes also allow toxins to get in, which kills the cell and everything in it (e.g. viruses that invaded)
> B-cells are stimulated
> Stimulate phagocytosis by phagocytes
> Become T-memory cells
What can occur after Helper-T cells divide by mitosis in the cell-mediated response?
1) Cytotoxic T-Cells are stimulated –> Produces chemicals which make the APC’s membrane permeable which can kill the cell. The holes also allow toxins to get in, which kills the cell and everything in it (e.g. viruses that invaded)
2) B-cells are stimulated
3) Stimulate phagocytosis by phagocytes
4) Form T-memory cells
Give 2 differences between specific and nonspecific immune responses [4 marks]
Nonspecific =
> immediate response to all pathogens
> physical barriers (e.g. skin) and phagocytes
Specific =
> time lag - slower and specific to each pathogen
> includes cell-mediated response (T lymphocytes) & humoral response (B lymphocytes)
Name the 2 types of specific immune response.
Cell-mediated response
Humoral response
What kind of cells or molecules stimulate an immune response?
1) Pathogens
2) Abnormal cells - (cancer)
3) Foreign cells from other organisms of the same species - transplants
4) Toxins (released by pathogens)
What is another name for lymphocytes?
T cells
What are T cells / lymphocytes?
> WBCs involved In specific immune response - in cell-mediated response
> Made in bone marrow but T cells mature in thymus.
What will T-lymphocytes respond to?
Antigens of a pathogen attached to an APC
T cells will NOT respond to antigens directly still attached to a pathogen,
only antigens that have gone through phagocytosis.
What is an antibody?
Protein produced by B plasma cells which binds to a specific complementary antigen.
Describe the structure of an antibody
1) Antibodies are proteins with a quaternary structure
2) Made of 4 polypeptide chains…
> 2 heavy chains (large polypeptide chain)
> 2 light chains (small polypeptide chain)
3) The heavy and light polypeptide chains are held by DISULPHIDE bonds
4) Contains VARIABLE regions which form antigen binding sites
5) The rest of the antibody is CONSTANT.
http://www.biology.arizona.edu/immunology/tutorials/antibody/structure.html
Why is the antigen-binding site on an antibody specific to one antigen?
> Antibodies have different VARIABLE regions…
…with an antigen-binding site that is COMPLEMENTARY to one specific antigen/toxin produced by a pathogen.
(a) Name the monomer that forms the heavy and light chains in an antibody
(b) Name the chemical bonds that join these monomers [2 marks]
(a) Amino acids
(b) Peptide bonds
The specificity of an antibody depends on the variable regions.
Explain how [3 marks]
Variable regions have different sequence of amino acids (primary structure) [1]
Affects tertiary structure [1]
Only a specific antigen can bind [1]
What is the role of antibodies?
1) They form antibody-antigen complexes.
2) Neutralises toxins released by pathogens
3) Antibodies do not destroy pathogens DIRECTLY.
Antibodies & substances released from Helper T cells activate the B cell.
This is called clonal selection. The activated B cell divides into plasma cells.