3.2.4 Cell recognition and the immune system Flashcards
What specific molecules on cell surfaces enable identification by the immune system?
Proteins with specific tertiary structures that act as antigens.
What are the four things the immune system can identify using specific molecules on cell surfaces?
Pathogens, non-self cells (e.g. cells from other organisms of the same species), abnormal body cells (e.g. cancer cells), toxins.
What is the role of proteins on the surface of cells?
To act as antigens with specific tertiary structures which are recognized by the immune system.
Give an example of an abnormal body cell that the immune system can identify.
Cancer cells displaying abnormal antigens.
What term describes cells from other organisms of the same species that can be identified by the immune system?
Allogeneic cells identified as non-self.
What feature of toxins allows the immune system to identify them?
The specific shape of their antigenic determinants.
How does the immune system differentiate between self and non-self cells?
By recognizing antigens; self-cells display self-antigens while non-self cells display foreign antigens.
What is the definition of an antigen?
An antigen is a molecule, often a protein, with a specific tertiary structure that triggers a specific immune response by being recognized as non-self by the immune system.
How does antigen variability affect disease?
Antigen variability caused by genetic mutations or recombination changes the specific proteins on a pathogen’s surface. This helps pathogens evade immune recognition, leading to persistent or recurrent infections. For example, the influenza virus frequently alters its antigens, requiring updated vaccines.
How does antigen variability impact disease prevention?
Antigen variability reduces vaccine effectiveness because changes in surface antigens mean the immune system may not recognize the pathogen. Vaccines such as the flu vaccine must be updated regularly to match these new antigenic forms and maintain protection.
What is phagocytosis?
The process by which phagocytes engulf and ingest pathogens.
What happens to pathogens after phagocytosis?
Ingested pathogens are destroyed by lysozymes within the phagocyte.
What is the cellular response in the immune system?
The activation of T lymphocytes in response to a foreign antigen.
How do T lymphocytes respond to a foreign antigen?
T lymphocytes bind to antigens presented on the surface of antigen-presenting cells, leading to their activation and clonal expansion.
What is the role of antigen-presenting cells in the cellular response?
Antigen-presenting cells display antigens on their surface to activate T lymphocytes.
What is the role of helper T cells (TH cells) in the immune response?
Helper T cells stimulate cytotoxic T cells (TC cells) to kill infected cells, activate B cells to produce antibodies, and enhance the activity of phagocytes by releasing cytokines which amplify phagocytic activity.
What is the humoral response?
The activation of B lymphocytes in response to a foreign antigen, leading to the production of monoclonal antibodies.
What is clonal selection in the humoral response?
The process by which specific B lymphocytes with complementary receptors to the foreign antigen are activated and cloned.
What do B lymphocytes release after activation?
B lymphocytes release monoclonal antibodies specific to the foreign antigen.
What is the definition of an antibody?
An antibody is a protein produced by B lymphocytes that binds specifically to a complementary antigen, triggering its destruction.
What is the structure of an antibody?
Antibodies consist of four polypeptide chains (two heavy chains and two light chains) held together by disulfide bonds. They have a variable region that binds to a specific antigen and a constant region.
What happens when an antigen-antibody complex forms?
The formation of an antigen-antibody complex leads to the destruction of the antigen through agglutination and phagocytosis of bacterial cells.
What is the role of plasma cells in the immune response?
Plasma cells are activated B lymphocytes that produce and release large quantities of monoclonal antibodies during the primary immune response.
What is the role of memory cells in the immune response?
Memory cells are long-lived B lymphocytes that remain in the body after the primary immune response, enabling a faster and stronger secondary immune response upon re-exposure to the same antigen.
How do vaccines provide protection against disease?
Vaccines contain antigens from a pathogen, stimulating the production of memory cells without causing disease, leading to immunity.
What is herd immunity?
Herd immunity occurs when a significant portion of a population is vaccinated, reducing the spread of the disease and protecting individuals who are not immune.
What is active immunity?
Active immunity involves the production of antibodies by the immune system after exposure to an antigen, either through infection or vaccination.
What is passive immunity?
Passive immunity involves the transfer of antibodies from another source, such as maternal antibodies through the placenta or injection of antiserum, providing temporary immunity.
What are the differences between active and passive immunity?
Active immunity is long-lasting, involves memory cell formation, and takes time to develop, while passive immunity is immediate, short-term, and does not involve memory cells.
What is the structure of HIV?
HIV consists of an RNA genome enclosed in a capsid, surrounded by a lipid envelope embedded with glycoproteins.
How does HIV replicate in helper T cells?
HIV binds to the CD4 receptors on helper T cells using its glycoproteins, fuses with the cell membrane, and releases its RNA. Reverse transcriptase converts the RNA into DNA, which integrates into the host’s genome. The host cell machinery produces new viral particles.
How does HIV cause the symptoms of AIDS?
HIV destroys helper T cells, reducing their numbers and impairing the immune response. This makes the body susceptible to opportunistic infections and cancers.
Why are antibiotics ineffective against viruses?
Antibiotics target bacterial structures and metabolic pathways, such as cell walls and ribosomes, which are absent in viruses. Consequently, antibiotics cannot disrupt viral replication.
How are monoclonal antibodies used in targeting medication?
Monoclonal antibodies are attached to therapeutic drugs. These antibodies bind specifically to antigens on target cell types, delivering the drug directly to the diseased cells and minimizing side effects.
How are monoclonal antibodies used in medical diagnosis?
Monoclonal antibodies are used to detect specific antigens or proteins in diagnostic tests, such as detecting biomarkers for diseases like cancer or infections.
What are some ethical issues associated with the use of vaccines?
Ethical issues include concerns about testing vaccines on animals or humans, the cost and accessibility of vaccines, and the potential side effects.
What are some ethical issues associated with the use of monoclonal antibodies?
Ethical issues include the use of animals in their production, the cost of treatment, and the potential for side effects.
What is the purpose of the ELISA test?
The ELISA test detects the presence and quantity of specific antigens or antibodies in a sample, such as diagnosing infections like HIV. Detecting antigens allows for early diagnosis of disease, while detecting antibodies indicates an immune response to a pathogen.
How does the ELISA test work?
The test involves attaching an antigen or antibody to a surface, adding the sample, and using enzyme-linked antibodies that produce a color change to indicate a positive result.
Describe the role of the disulfide bridge bonds in an antibody
joins two (different) polypeptides
Explain why antibodies will only bind with specific antigens.
antibodies have a variable region that has a specific amino acid sequence OR primary structure
the shape OR tertiary structure of the binding site is complementary to specific antigens
forms a complex between the antigen and antibody OR forms an antigen-antibody complex
Describe how phagocytes destroy pathogens.
engulfs/endocytosis
forms a vesicle/phagosome AND fuses with a lysosome
enzymes/lysozymes digest/hydrolyse the pathogen
What is an antigen?
a molecule/protein/glycoprotein
that stimulates an immune response
Other than pathogens, give two types of cell that may stimulate an immune response.
cells from other organisms OR cells from transplants
abnormal/cancer/tumour cells
cells infected by a virus
own/host cells in an autoimmune disease
Explain how the release of antibodies stimulates the process of phagocytosis.
antibodies bind to antigens
OR
antibodies are markers/opsonins
OR
antibodies form antigen-antibody complexes
antibodies cause clumping/agglutination
OR
antibodies attract phagocytes
Explain why a high mutation rate makes it difficult to develop a vaccine.
high mutation rate leads to the antigens changing
OR
high mutation rate leads to antigenic variability
vaccines (often) contain a specific antigen
antibodies will not be complementary to a changed antigen
OR
antibodies will not bind to changed antigens
Explain how HIV affects the production of antibodies when AIDS develops.
less/no antibodies produced
because HIV destroys helper T cells
so few/no B cells are activated
OR
few/no B cells undergo mitosis
OR
few/no B cells differentiate into plasma cells
Explain how the destruction of T cells by HIV eventually leads to death of the affected individual.
nsufficient/no T cells to activate B cells
OR
insufficient/no T cells to activate the immune system
individual unable to fight off infections/cancer/diseases
OR
individual more prone to infections/cancer/diseases
example of infection/cancer/disease (e.g. TB/tuberculosis or pneumonia)
What is an antibody?
a protein/immunoglobulin specific to an antigen
produced by B cells OR secreted by plasma cells
Explain how vaccines can be used to protect people against disease.
vaccines contain antigens
OR
vaccines contain dead/weakened pathogens
memory cells are made
on second exposure to the antigen/pathogen, memory cells (divide into plasma cells that) produce antibodies
memory cells rapidly (divide into plasma cells that) produce antibodies
OR
memory cells (divide into plasma cells that) produce more antibodies
antibodies destroy pathogens
Explain the differences between active and passive immunity.
active immunity involves memory cells, passive immunity does not
active immunity involves the production of antibodies by plasma cells
passive immunity involves antibodies being introduced into the body from outside
active immunity is long term because antibodies are produced in response to antigens
passive immunity is short term because the antibodies given are broken down
active immunity can take time to develop, passive immunity is fast acting
Describe how HIV is replicated. (4)
- Attachment proteins attach to receptors on helper T cell/lymphocyte;
- Nucleic acid/RNA enters cell;
- Reverse transcriptase converts RNA to DNA;
- Viral protein/capsid/enzymes produced;
- Virus (particles) assembled and released (from cell);
Describe how a phagocyte destroys a pathogen present in the blood. (3)
- Engulfs;
Accept endocytosis
OR
Description
Ignore ‘taken in’
- Forming vesicle/phagosome and fuses with lysosome;
- Enzymes digest/hydrolyse;
Accept lysozymes for ‘enzymes’
Give two types of cell, other than pathogens, that can stimulate an immune
response. (2)
- (Cells from) other organisms/transplants;
- Abnormal/cancer/tumour (cells);
- (Cells) infected by virus;
Accept ‘own cells’ if autoimmune response
suggested
Accept APCs
Accept non-self
What is the role of the disulfide bridge in forming the quaternary structure
of an antibody?
Joins two (different) polypeptides;
Explain how HIV affects the production of antibodies when AIDS develops
in a person. (3)
- Less/no antibody produced;
- (Because HIV) destroys helper T cells;
Accept ‘reduces number’ for ‘destroys’ - (So) few/no B cells activated / stimulated
OR
(So) few/no B cells undergo mitosis/differentiate/form plasma cells;
Determining the genome of the viruses could allow scientists to develop a
vaccine.
Explain how. (2)
- (The scientists) could identify proteins (that derive from the genetic code)
OR
(The scientists) could identify the proteome; - (They) could (then) identify potential antigens (to use in the vaccine);
Reject if answer suggests vaccine contains
antibodies
What is a monoclonal antibody? (1)
(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. (1)
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. (4)
- (First) antibody binds/attaches /complementary (in shape) to antigen;
- (Second) antibody with enzyme attached is added;
- (Second) antibody attaches to antigen;
Accept (second) antibody attaches to (first) antibody
(indirect ELISA test).
- (Substrate/solution added) and colour changes;
Only award if enzyme mentioned.
Describe and explain the role of antibodies in stimulating phagocytosis.
Do not include details about the process of phagocytosis. (2)
- Bind to antigen
OR
Are markers;
Accept opsonin for ‘marker’
Accept form (antibody-antigen) complexes/are
complementary to antigen
- (Antibodies) cause clumping/agglutination
OR
Attract phagocytes;
Reject clotting
Describe how phagocytosis of a virus leads to presentation of its antigens. (3)
- Phagosome / vesicle fuses with lysosome;
- (Virus) destroyed by lysozymes / hydrolytic enzymes;
- Peptides / antigen (from virus) are displayed on 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 / TH cell binds to the antigen (on the antigen-
presenting cell / phagocyte); - This helper T / TH cell stimulates a specific B cell;
- B cell clones
OR
B cell divides by mitosis; - (Forms) plasma cells that release antibodies;
What is an antigen? (2)
- Foreign protein;
Accept glycoprotein / glycolipid / polysaccharide
- (that) stimulates an immune response / production of antibody;
What is an antibody? (2)
- A protein / immunoglobulin specific to an antigen;
- Produced by B cells
OR
Secreted by plasma cells;
When a vaccine is given to a person, it leads to the production of antibodies against a disease-causing organism.
Describe how. (5)
- Vaccine contains antigen from pathogen;
- Macrophage presents antigen on its surface;
- T cell with complementary receptor protein binds to antigen;
- T cell stimulates B cell;
- (With) complementary antibody on its surface;
- B cell secretes large amounts of antibody;
- B cell divides to form clone all secreting / producing same
antibody.
Describe the difference between active and passive immunity.
- Active involves memory cells, passive does not;
- Active involves production of antibody by plasma cells /
memory cells; - Passive involves antibody introduced into body from outside /
named source; - Active long term, because antibody produced in response to
antigen; - Passive short term, because antibody (given) is broken down;
- Active (can) take time to develop / work, passive fast acting.
Describe how phagocytosis of a virus leads to presentation of its antigens
- Phagosome/vesicle fuses with lysosome;
- (Virus) destroyed by lysozymes/hydrolytic
enzymes; - Peptides/antigen (from virus) are displayed on
the cell membrane;
Describe how presentation of a virus antigen leads to the secretion of an antibody
against this virus antigen.
- Helper T cell/TH cell binds to the antigen (on
the antigen-presenting cell/phagocyte); - This helper T/TH cell stimulates a specific B
cell; - B cell clones
OR
B cell divides by mitosis; - (Forms) plasma cells that release antibodies;
