Unit 2 - Cell Recognition + The Immune System Flashcards
What is an antigen?
A foreign molecule that stimulates an immune response. They are often proteins or glycoproteins.
Definition of foreign?
In biology, foreign means something which is not part of the host organism (your own body).
Antigens enable the immune system to identify what cells and molecules?
-Pathogens
-Abnormal body cells, e.g. cancer cells + infected cells
-Toxins
-Cells from other individuals of the same species.
What are pathogens?
Pathogens are microorganisms that cause disease, e.g. bacteria, fungi + viruses.
How do pathogens cause disease?
By damaging/killing cells and tissues and producing toxins.
What are phagocytes?
White blood cells that carry out phagocytosis, which involves engulfing the foreign antigen.
What is the 1st stage of the immune response and why is it nonspecific?
Stage 1 = Phagocytosis.
It is nonspecific because phagocytes will engulf anything foreign.
Steps of phagocytosis?
1) Phagocyte recognises the antigen as foreign.
2) The pathogen is engulfed by the phagocyte.
3) Engulfed pathogen is contained inside a vesicle called a phagosome.
4) Lysosomes fuse with the phagosome releasing lysozymes into the phagosome.
5) Lysozyme enzymes hydrolyse the molecules, e.g. proteins in the pathogen.
6) The antigens from the pathogen are presented on the cell surface membrane of the phagocyte - the phagocyte becomes an antigen presenting cell.
Acronym to remember phagocytosis?
Phagocyte
Recognises foreign antigen
Engulfs antigen
Phagosome
Fuses (lysosome)
Enzymes (lysozymes)
Hydrolyse
Antigen presented
Membrane
Acronym=Penis Reaches Extreme Places for Extreme Happiness A-Men.
What is the 2nd stage of the immune response?
Specific immune response. It would take too long to destroy a pathogen using only just phagocytosis, so a specific response is initiated where a specific foreign antigen is targeted.
What are helper t-cells?
White blood cells that have protein receptors in their cell membrane.
How are t-cells activated?
Helper t-cell with specific complementary receptor, binds to antigen on antigen presenting cell and the t-cell is activated.
The activated t-cell then releases chemical signals (cytokines) which further activates what?
-More phagocytes.
-Cytotoxic t-cells which kill infected cells directly.
-Specific B-cells also a type of white blood cell.
What is part 1 of stage 2?
The cellular response - T cells.
Acronym for cellular response (t-cells)?
An antigen presenting cell
Activates
Specific
T-cell
Clones (mitosis)
Cytotoxic t-cells
Helper T cells
Stimulating
B-cells
Phagocytes
Acronym = An Awesome Shag Touches Clit Carefully He Should Be Proud
What is part 2 of stage 2?
Humoral response - B cells.
How are specific b cells activated?
By their specific helper T cell.
What is the humoral response?
1) Specific B cells are activated by their specific helper T cell.
2) B cells clone into memory cells and plasma cells.
3) Plasma cells secrete specific antibodies which bind the foreign antigen.
Acronym for the humoral response?
T helper cell (specific)
Activates
B cell (specific)
Clones by mitosis
Plasma cells
Antibodies
Memory cells
Acronym = To Activate Boner Chew Penis All Morning.
What do plasma cells release?
Many monoclonal antibodies which have binding sites complementary to the same antigen and bind, leading to the destruction of the pathogen through agglutination and phagocytosis.
Definition of monoclonal antibodies?
Antibodies with the same tertiary structure, which are complementary to and bind one type of antigen. They come from the same type of B cell.
What is the primary immune response?
Helper T cells activating B cells to result in antibody production. This occurs each time you come across a new antigen that you have not been exposed to before.
What is the secondary immune response?
Memory B cells have an antibody with the same tertiary structure, complementary to the same antigen as the parent B cell. So if re-infected with the same antigen, memory B cells with the complementary antibody:
-bind the antigen
-clone into plasma cells
-produce many more antibodies, more quickly to kill the foreign cell.
Structure of an antibody?
Describe the structure of an antibody?
They have a quaternary structure made up of 4 polypeptide chains, 2 heavy chains and 2 light chains, held together by disulphide bridges. It’s a protein!
What are the 2 regions in an antibody?
Constant region = has the same tertiary structure in all antibodies.
Variable region = contains the binding site for antigens and differs between antibodies making antibodies complementary to only one type of antigen.
When an antibody binds to an antigen it is known as?
An antigen-antibody complex.
What is agglutination?
Antigen-antibody complexes cause the foreign cells to clump together as each antibody has 2 binding sites, which can bind to 2 antigens at the same time on different cells. This allows many cells to be engulfed by a phagocyte in one go.
Summary of the immune response? (Use this to answer 5 mark questions on the primary immune response)
1) A phagocyte engulfs the pathogen, hydrolyses it and presents antigens on its surface membrane.
2) Specific helper T cell with a complementary receptor protein binds to the antigen.
3) This helper T cell binds to and activates a specific b cell.
4) The specific b cell clones by mitosis into plasma cells which make and secrete many antibodies with specific binding sites complementary to the antigen.
5) The antibodies agglutinate the antigens, which are destroyed by phagocytes.
6) Memory b cells with the complementary antibody remain and clone into plasma cells when presented with the same antigen, producing many more antibodies, faster.
