Topic 2C: Cells and the Immune System Flashcards
What is a pathogen? [1]
A microorganism (e.g. bacteria, fungi, protists) or viruses that cause infectious disease.
What is a toxin?
A poisonous substance produced by living organisms
What is an antigen?
A foreign molecule (usually a protein) that stimulates an immune response
When a pathogen enters the body it may be destroyed by phagocytosis.
Describe how. [4]
- Phagocyte attracted by a substance / recognises (foreign) antigen;
- (Pathogen) engulfed;
- Enclosed in vesicle/phagosome;
- (Phagosome) fuses with lysosome;
- Lysosome contains lysozymes;
- Pathogen digested (by lysozymes).
What is an antibody?
A protein capable of binding a specific antigen
Why do antibodies have a quaternary structure? [1]
- More than one / four polypeptide chains
Explain why an antibody binds to a specific antigen. [3]
- Antibody / variable region has specific amino acid sequence / primary structure;
- The shape / tertiary structure of the binding site is complementary to / binds with these antigens;
- Forms complex between antigen and antibody.
Describe how a phagocyte destroys a pathogen present in the blood. [3]
- Engulfs;
- Forming phagosome and fuses with lysosome;
- Enzymes digest.
Give two types of cell, other than pathogens, that can stimulate an immune response. [2]
- (Cells from) other organisms/transplant;
- Abnormal/cancer/tumour (cells);
- (Cells) infected by virus.
What is the role of disulphide bridges in forming the quaternary structure of an antibody? [1]
- Joins (different) polypeptides
Describe how phagocytosis of a virus leads to presentation of its antigens. [3]
- Phagosome fuses with lysosome;
- (Virus) destroyed by lysozymes;
- Antigen (from virus) displayed in the cell membrane
Describe how presentation of a virus antigen leads to the secretion of an antibody against this virus antigen. [3]
- Helper T cell binds to the antigen (on the antigen-presenting cell/phagocyte);
- This helper T cell stimulates a specific B cell;
- B cell divides by mitosis;
- (Forms) plasma cells that release antibodies.
What are monoclonal antibodies? [1]
Antibodies with the same tertiary structure produced from a genetically identical set of plasma cells.
How is immunity achieved?
Through the presence of antibodies against the antigens of that pathogen in a person’s body.
How does a vaccine make someone immune to a pathogen? [5]
- (Vaccine contains) antigen / attenuated/dead/inactive pathogen;
- (Specific) helper T cell stimulates B cell specific to antigen;
- B cell clones/divides by mitosis;
- Plasma cells release antibodies;
- Memory cells produced meaning higher concentration of antibodies/antibodies produced faster in secondary response/on infection with the actual pathogen.
What is herd immunity?
A form of indirect protection from infectious disease that occurs when a sufficient percentage of a population has become immune to an infection, reducing the likelihood of infection spreading to individuals who lack immunity.
Describe how B lymphocytes would respond to a vaccination against a virus.
Do not include details of the cellular response in your answer. [3]
- B cell binds to specific/complementary (viral) antigen;
- B cell divides by mitosis;
- (B cells develop into) plasma cells that release antibodies (against the virus);
- (B cells develop into) memory cells
What is an allergic reaction?
An immune response to an otherwise harmless substance.
Explain how treatment with antivenom works and why it is essential to use passive immunity, rather than active immunity. [2]
- (Antivenom) antibodies bind to the toxin/venom/antigen and (causes) its destruction;
- Active immunity would be too slow.
When making an antivenom, a mixture of venoms from several snakes of the same species is used.
Suggest why. [2]
- May be different form of antigen/toxin (within one species);
- Different antibodies (needed in the antivenom)
During the production of antivenom, the animals used are under ongoing observation by a vet.
Suggest one reason why. [1]
- (So) the animal does not suffer from the venom/vaccine/toxine;
- (So) the animal does not suffer anaemia/does not suffer as a result of blood collection;
- (So) the animal does not have pathogen that could be transferred to humans.
During vaccination, each animal is initially injected with a small volume of venom. Two weeks later, it is injected with a large volume of venom.
Use your knowledge of the hum oral immune response to explain this vaccination programme. [3]
- B cells specific to the venom reproduce by mitosis;
- (B cells produce) plasma cells and memory cells;
- The second dose produces antibodies (in secondary immune response) in higher concentration and quickly
NMO is a disease that leads to damage to nerve cells in the spinal cord. A person with NMO produces anti-AQP4 antibody that attacks only these nerve cells.
Explain why the anti-AQP4 antibody only damages these cells. [4]
- (Anti-AQP4) antibody has a (specific) tertiary structure;
- Has binding site / variable region that only binds/complementary to one antigen;
- Antigen to this antibody (only) found in these nerve cells;
- So, antibody (only) binds to / forms antigen-antibody complex with these nerve cells (causing damage).
Describe the structure of the human immunodeficiency virus (HIV). [4]
- RNA (as genetic material);
- Reverse transcriptase;
- (Protein) capsid;
- Phospholipid viral envelope;
- Attachment proteins
Describe how the human immunodeficiency virus (HIV) is replicated once inside helper T cells. [4]
- RNA converted into DNA using reverse transcriptase;
- DNA inserted into DNA;
- DNA transcribed into (HIV m)RNA;
- (HIV mRNA) translated into viral proteins (for assemble into viral particles)
The ELISA test only detects the presence of HIV antibodies. Give two reasons why it cannot be used to find out if a person has AIDS. [2]
(To diagnose AIDS, need to look for)
1. (AIDS-related) symptoms;
2. Number of helper T cells
In the ELISA test, the solution will remain yellow if a person is not infected with HIV. Explain why. [2]
- HIV antibody is not present;
- (So) second antibody/enzyme will not binds / is not present
A mother who was infected with HIV gave birth to a baby. The baby tested positive using this test. This does not prove the baby is infected with HIV.
Explain why. [2]
- Children receive antibodies from their mothers;
- (So) solution will always test positive
Describe the role of antibodies in producing a positive result in an ELISA test. [4]
- (First) antibody binds to antigen;
- (Second) antibody with enzyme attached is added;
- (Second) antibody attaches to antigen;
- (Substrate added) and colour change
Explain why the number of HIV particles in the blood rises during the first few months after infection. [2]
- (HIV is) invading cells which make new viruses;
- Cells release viruses into blood
Explain why the number of HIV particles in the blood can remain low for many years after infection. [1]
- Virus remains dormant/exists as DNA in host DNA
Describe how HIV is replicated after it has entered a human cell. [4]
- Reverse transcriptase;
- Enzyme uses (HIV) RNA to make DNA (copy);
- DNA joined to (host) cell’s DNA;
- DNA used to make HIV RNA (copies);
- And HIV capsid proteins;
- Made at (host) ribosomes;
- Assembly of new virus particles;
- Budding off from membrane (of host cell)
The destruction of T-cells by HIV leads to death of an infected person.
Explain how. [2]
- Not enough T-cells to activate B-cells;
- Person unable to fight infections/cancer
What is an antigen? [2]
- Molecule/protein;
- Stimulates immune response;
- (That causes) production of antibodies
Explain why antibodies against Salmonella do not normally bind to HIV. [2]
- Antigens on HIV are different shape;
- So antibody not complementary to antigen;
- Receptor sites on antibody specific to one antigen
HIV infects some human cells, such as T-cells, but not others.
Suggest why. [2]
- HIV binds to specific receptor;
- Only present on certain cells
Antibiotics are not used to treat viral infections, such as HIV.
Explain why. [2]
- Antibiotics stop metabolism, viruses don’t have metabolism;
- Viruses hide in cells, antibiotics can’t reach
