Unit 2.4 - Cell recognition and the immune system Flashcards
How do bacteria cause harm?
Produce toxins that damage cells
How do viruses cause harm?
Use host cells to replicate and then burst/destroy them
Difference between non-specific and specific defence mechanisms?
Non-specific act quickly but respond in the same to all pathogens
Specific act slower but produce a specific response for each pathogen
What are the two types of specific immune responses called?
Cell mediated which involve T lymphocytes
Humoral which involve B lymphocytes
Summarise the steps of phagocytosis
Phagocyte is attracted to the pathogen by the pathogen’s chemical products which act as attractants.
Phagocyte has several receptors on its cell surface membrane which attach to antigens on the surface of the pathogen.
The phagocyte engulfs the pathogen and forms a vesicle known as a phagosome.
Lysosomes within the phagocyte migrate towards the phagosome
Enzymes present called lysozymes hydrolyse the cell walls of the the ingested bacteria.
Define an antigen
A molecule recognised as foreign and triggers an immune response
Usually proteins or glycoproteins
Define antibody
A protein secreted by B cells in response to an antigen.
Steps of the humoral response ?
A B cell a complementary antibody to the antigen comes and binds to it.
The B cell takes in the antigen and processes it before displaying it on its cell surface membrane.
An activated Th cell binds to the antigen and activates the B cell to divide. This is clonal selection.
The activated B cell then divides by mitosis to form plasma cells and memory cells this is called clonal expansion.
The plasma cells which are produced then go on to synthesise and release specific antibodies which are complimentary to the antigen on the pathogen’s surface. The antibodies bind to the antigens on the surface of the pathogen which leads to its destruction.
Memory cells are also produced which remain dormant in the blood, ready to divide into plasma cells if re-infected by the same pathogen. Responding rapidly.
What type of biological molecule is an antibody?
Protein
How many molecules combine to form an antibody?
4 polypetide chains
What type of bond holds the molecules together in an antibody?
Disulphide bridges
What is agglutination and how does it affect the immune response?
The clumping together of pathogens by antibodies.
Makes it easier for the phagocytes to locate
What is a monoclonal antibody
Antibodies of a single specificity derived from a single clone of B cells
What is a polyclonal antibody?
Mixture of antibodies with different specificities derived from multiple clones of B cells.
What is antigen variation?
When the antigen on the surface of the pathogen changes caused by the mutation of the gene that codes the antigens.
Therefore when you are infected for a second time instead of a secondary immune response the body goes through another primary response as the memory cells that are produced in the first response will no longer recognise the antigen.
Why is influenza prone to muation?
As it is made from RNA which is more prone to mutation than DNA
Define immunity
The ability of an organism to protect itself from/ respond rapidly to an infection.
What type of immunity is a vaccine?
Artificial active immunity
What is meant by the term vaccination?
The introduction of antigens from a pathogen into the body to stimulate active immunity against it and produce memory cells. `
Steps of cell mediated immunity?
Pathogens are engulfed by phagocytes and then the phagocyte presents the pathogen’s antigens on its cell surface membrane.
Receptors on a specific helper T cell fit complementary to these antigens.
The attachment stimulates the T cell to divide rapidly by mitosis. This is called clonal expansion.
The cloned T cells develop into:
- Memory cells that can develop rapidly into cytotoxic T cells if reinfection occurs by the same pathogen.
- Stimulate phagocytes to engulf pathogens by phagocytosis
- Stimulate B cells to divide and secrete their antibodies.
- Activate Cytotoxic T cells
What is the role of Cytotoxic T cells?
They kill abnormal and body cells that are infected by pathogens.
They do this by producing a protein called perforin which perforates the cell membrane making it freely permeable.
Differences between humoral and cell mediated immunity?
Humoral involves mainly B cells.
CM involves T cells
Humoral B cells produced and develop in the bone marrow
CM T cells produced in bone marrow and develop in the thymus gland
Humoral produces antibodies
CM doesn’t produce antibodies
Humoral kills pathogens via antibodies - agglutination and phagocytosis
CM kills pathogens by specialised cytotoxic T cells
Uses of monoclonal antibodies?
Diagnosis of Diseases - Monoclonal antibodies bind to specific cells identifying if they’re infected or not
Treatment of Diseases - Monoclonal antibodies bind to specific cells and can bring theraputic drugs with them
Pregnancy testing - Monoclonal antibodies bind to pregnancy hormones
Detecting certain cancers - MA can bind to specific antigens eg. Prostate specific antigens to identify prostate cancer
Difference between direct and indirect ELISA test
Direct uses one monoclonal antibody
Indirect uses two
How can the ELISA test be used to test for diseases?
Uses monoclonal antibodies to detect both the presence and quantity of protein in a sample.
Outline the steps of the Indirect Elisa test?
Add the sample to a well plate where the target protein attaches to a wall
Add the antibody that is specific to the target protein
Wash to remove all unbound anitbodies
Add a second antibody that attaches to the first one - These second antibodies carry a protein.
Was to remove all unbound antibodies
Add a solution containing a substrate to the well. The secondary antibody will act on the substrate and cause a colour change.
Structure of HIV
Two RNA strands and enzymes eg. reverse transcriptase within a capsid.
The capsid is surrounded by a lipid envelope which have attachment proteins on it.
Just inside the lipid envelop are matrix proteins which allow HIV to remain its structure
How is HIV replicated?
Once infected HIV particles circulate in the blood stream
HIV attachment proteins bind to Th cells
HIV lipid envelop fuses with cell membrane of Th cell.
Capsid and its content pass into Th cell.
Reverse transcriptase converts RNA to DNA
DNA moves into cell nucleus and integrates with host DNA.
HIV DNA transcribes mRNA to encode for HIV viral proteins.
mRNA is transcribed into viral proteins
Virus particles assemble
Why can antibiotics not be used to treat HIV?
Viruses have no cellular structure which antibiotics target.
They also use the metabolic processes of the host cells so they cannot be targeted either.
How is HIV treated?
Using antiviral drugs which inhibit enzymes such as reverse transcriptase
Why is vaccination not always successful in eliminating disease?
Vaccination can fail to induce immunity in certain people if they have defective immune systems
Individuals may become develop the disease immediately after vaccination before their immunity levels are high enough
Antigens may mutate - antigen variability
Ethical issues around vaccinations?
Animal testing
Side effects that can cause long term harm
Human trials
Should they be compulsory to achieve herd immunity?
