3.2.4 Cell recognition and the immune system Flashcards
(83 cards)
1
Q
What are the 4 types of pathogen?
A
Bacteria, Viruses, Protoctists, Fungi
2
Q
What do Bacteria do?
A
Bacteria produce toxins that damage body cells.
3
Q
What do Viruses do?
A
Viruses use host cells to replicate before bursting out and destroying cells.
4
Q
What do Protoctists do?
A
Protoctists take over cells and break them open.
5
Q
What do Fungi do?
A
Fungi digest living cells to destroy them and some produce toxins.
6
Q
What are the 2 types of defence mechanisms?
A
Non-specific and Specific
7
Q
What are non-specific defences?
A
These act quickly to defend the body, but respond in the same way for all pathogens.
8
Q
What are examples of non-specific defences?
A
Physical and Chemical Barriers and Phagocytosis
9
Q
What are specific defences?
A
These are slower to defend the body, but produce a specific response for each pathogen and also provide long term immunity against specific pathogens.
10
Q
What are examples of specific defences?
A
Cellular Response and Humoral Response
11
Q
What are examples of physical and chemical barriers?
A
Skin, Mucous membranes, Expulsive reflexes, Blood clotting and wound repair.
12
Q
What are antigens?
A
Antigens are usually proteins that can be found on the surface of cells and they trigger an immune response. Antigens allow the immune system to distinguish between the body’s own cells and foreign cells.
13
Q
What cells and molecules do antigens allow the immune system to identify?
A
Pathogens, Abnormal Body Cells, Toxins and Cells from other organisms of the same species
14
Q
Pathogens.
A
The immune system recognises antigens as being foreign and activates cells to destroy the pathogen.
15
Q
Abnormal Body Cells.
A
Cancerous or infected cells display abnormal antigens that trigger an immune response.
16
Q
Toxins.
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These are antigen molecules themselves and can be recognised by the immune system.
17
Q
Cells from other organisms of the same species.
A
These cells may have different antigens to the body’s own cells and so are identified as being foreign. This can cause the rejection of transplanted organs.
18
Q
What are Phagocytes?
A
Phagocytes are a type of white blood cell that engulf and destroy pathogens by phagocytosis. They are found in the blood and body tissues of organisms.
19
Q
What is the process of phagocytosis?
A
- The pathogen releases chemicals that attract a phagocyte.
- The phagocyte recognises the pathogen’s antigens as non-self. This causes the phagocyte to bind to the pathogen.
- The phagocyte engulfs the pathogen.
- The pathogen is now contained within a vesicle known as a ‘phagosome’.
- The lysosome, containing hydrolytic enzymes called lysozymes, fuses with the phagosome to form a phagolysosome.
- Lysozymes digest and destroy the pathogen.
- The phagocyte presents the pathogen’s antigens on its surface to activate other cells in the immune system. The phagocyte is then referred to as an antigen-presenting cell (APC).
8.
20
Q
What is a lymphocyte?
A
Lymphocytes are type of white blood cell and are produced in the bone marrow.
21
Q
What are the 2 types of lymphocytes?
A
T lymphocytes or T cells and B lymphocytes or B cells.
22
Q
What are T lymphocytes/cells?
A
T cells mature in the thymus gland and they are involved in the cellular response where they respond to antigens presented on body cells.
23
Q
What are B lymphocytes/cells?
A
B cells mature in the bone marrow and they are involved in the humoral response where they produce antibodies found in body fluids.
24
Q
What are the different types of T cells?
A
Helper T cells, Cytotoxic T cells and Memory T cells.
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What do Helper T Cells do?
Helper T Cells have receptors on their cell-surface that bind to complementary antigens on antigen-presenting cells. After binding, they can form memory cells, stimulate B cells or phagocytes, and activate cytotoxic T cells.
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What do Cytotoxic T Cells do?
Cytotoxic T Cells kill abnormal and foreign cells by producing a protein known as perforin. This protein makes holes in the cell-surface membrane, causing it to become freely permeable and causing cell death.
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What do Memory T Cells do?
Memory T Cells provide long-term immunity against specific pathogens. They provide a rapid response if the body is re-infected by the same pathogen.
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What is the cellular response?
The cellular response is the response of T lymphocytes to a foreign antigen present on body cells.
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What is the process of the cellular response?
1. Phagocytes engulf pathogens and display their antigens on the cell-surface. They are now known as antigen-presenting cells.
2. Helper T cells with complementary receptors bind to these antigens.
3. On binding, the helper T cell is activated to divide by mitosis to form genetically identical clones.
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What are the different functions that cloned T cells can carry out? (4)
1. Develop into memory cells which circulate in the body to provide long-term immunity.
2. Stimulate phagocytosis as cloned cells stimulate phagocytes to engulf pathogens.
3. Stimulate division of B cells to divide and produce antibodies.
4. Activate cytotoxic T cells which then kill infected cells.
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What is the humoral response?
The humoral response involves the response of B lymphocytes to a foreign antigen in body fluids, clonal selection and the release of monoclonal antibodies.
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What cells are involved in the humoral response?
B cells, Plasma cells, Memory cells and Helper T cells.
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What do the B cells do?
B cells have antibodies on their cell-surface membrane that bind to complementary antigens.
On doing so, they engulf the antigens and display them on their cell-surface to become antigen-presenting cells. Once activated, B cells can divide into plasma cells and memory cells.
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What are Plasma cells?
Plasma cells are types of B cell that can produce and secrete antibodies against a specific antigen. They have a short lifespan of only a few days.
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What are memory cells?
Memory cells are types of B cell that provide long-term immunity against specific pathogens.
They have a much longer lifespan than plasma cells. They rapidly divide into plasma cells if the body is re-infected by the same pathogen.
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What do Helper T cells do?
These cells bind to antigen-presenting cells to activate the division of B cells.
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What are the Stages of the Humoral Response?
1. B cell with a complementary antibody binds to the antigens on a pathogen.
2. The B cell engulfs the pathogen and presents its antigens on the cell-surface membrane to become an antigen-presenting cell.
3. Clonal selection - Activated T helper cells bind to the B cell, causing activation of this B cell.
4. Clonal expansion - The activated B cell divides by mitosis to form plasma and memory cell clones.
5. The cloned plasma cells produce and secrete the specific antibody which is complementary to the antigen on the pathogen's surface. These antibodies attach to antigens on pathogens and destroy them.
6. The memory cells circulate the blood and tissue fluid, ready to divide if the body is re-infected by the same pathogen.
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What is Clonal selection?
The B cell with the correct antibody is selected for cloning (by being activated by a T helper cell).
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What is Clonal expansion?
The division of specific B cells to produce genetically identical clones.
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What are the 2 types of immune response?
1. Primary Immune Response
2. Secondary Immune Response
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What is the Primary immune response?
The primary immune response takes place when the body is exposed to a pathogen for the first time. This response is slow and the infected individual experiences symptoms of the disease.
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What is the Secondary immune response?
The Secondary immune response takes place when when the body has been exposed to the same pathogen before. This response is much faster and stronger and pathogens are destroyed before any symptoms appear.
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The process of the primary immune response?
1. The production of antibodies is slow after the first exposure to the pathogen (longer lag phase).
2. The concentration of antibodies increases slowly.
3. This is because there are very few B cells that are specific to the pathogen's antigens.
4. It takes time for the B cells to divide into plasma cells to produce the correct antibody, so the individual experiences symptoms of the disease.
5. During this process, some B cells divide into memory cells to make the individual immune to this disease.
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The process of the secondary immune response?
1. The production of antibodies is much quicker after exposure to the pathogen (shorter lag phase).
2. The concentration of antibodies increases quickly.
3. This is because memory cells recognise the pathogen's antigens and quickly divide into plasma cells.
4. These plasma cells secrete larger numbers of antibodies to quickly destroy the pathogen before the individual experiences any symptoms.
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What is the structure of an antibody?
Antibodies are Y-shaped glycoproteins made up of four polypeptide chains, two heavy chains, and two light chains. The polypeptide chains are held together via disulphide bridges.
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What are the various regions antibodies are made up of?
Constant region and Variable region
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What is the constant region?
The constant region is the same for all antibodies and binds to receptors on cells such as B cells.
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What is the Variable region?
The variable region is different for each antibody as its shape is complementary to a specific antigen. This is the part of the antibody that binds to antigens.
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What is the function of an antibody?
The main function of antibodies is to bind to specific antigens on a pathogen's surface. Each antibody has a unique binding site (in the variable region) that fits onto a specific antigen. When an antibody binds to an antigen, they form an antigen-antibody complex.
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What are the 3 roles antibodies carry out to help destroy pathogens?
1. Agglutination of pathogens
2. Neutralisation of toxins
3. Preventing pathogens from binding
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What is Agglutination of pathogens?
Antibodies act as agglutinins, causing pathogens to clump together. This makes it easier for phagocytes to locate pathogens and allows them to engulf a number of pathogens at once.
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What is Neutralisation of toxins?
This is when antibodies bind to toxins to inactivate them. Antibodies can act as antitoxins where they bind to toxins produced by pathogens. This binding neutralises (inactivates) the toxins to prevent them from damaging body cells.
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What is Preventing pathogens from binding?
When antibodies bind to a pathogen's antigens, they block cell-surface receptors needed to bind to host cells. This means that the pathogen cannot bind to or invade host cells therefore stops them from infecting body cells.
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What are Monoclonal Antibodies?
Monoclonal antibodies are antibodies produced from a single clone of plasma cells. Each of these antibodies are identical to one another and so will bind to a specific molecule.
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What are the uses of Monoclonal antibodies?
1. Diagnosis of disease - Monoclonal antibodies bind to specific cell types to identify infected cells.
2. Treatment of disease - Monoclonal antibodies bind to specific cells, bringing therapeutic drugs with them.
3. Pregnancy testing - Monoclonal antibodies bind to a pregnancy hormone in home pregnancy testing kits.
4. Detecting certain cancers - For example, monoclonal antibodies can bind to prostate specific antigens (PSA) to identify prostate cancer in men.
55
What is the ELISA test?
The Enzyme-Linked ImmunoSorbant Assay (ELISA) test uses monoclonal antibodies to to detect both the presence and quantity of protein in a sample. It is often used to find out whether a patient has antigens for a pathogen, and hence has the disease.
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What are the 2 types of ELISA test?
1. The direct test - This uses only one antibody.
2. The indirect test - This uses two antibodies.
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The steps of how the indirect ELISA test is carried out?
1. Add the sample (containing the target protein) to a well plate where the target protein can attach to the well.
2. Add the antibody that is specific to the target protein. These antibodies will bind to the target proteins attached to the well.
3. Wash the well to remove any unbound antibodies.
4. Add a second antibody that will bind to the first antibody. These secondary antibodies are attached to an enzyme.
5. Wash the well again to remove any unbound secondary antibody.
6. Add a solution containing substrate to the well. The enzyme attached to the second antibody will act on the substrate to cause a colour change. The intensity of the colour indicates the quantity of protein present.
55
What is Passive Immunity?
Passive immunity develops when an individual is given antibodies made by a different organism (the individual's immune system does not make these antibodies). This method provides immediate immunity to the disease, but it is short-term protection because the antibodies are broken down and memory cells are not produced.
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What are the 2 types of immunity?
1. Active Immunity
2. Passive Immunity
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What is Active Immunity?
Active immunity develops when the immune system makes its own antibodies after exposure to a pathogen's antigens. It takes a while to become immune to the disease, but it is long-term protection because memory cells are produced.
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What are 2 types of active immunity?
1. Natural - antibodies made after an infection.
2. Artificial - antibodies made after a vaccination
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What are the 2 types of passive immunity?
1. Natural - antibodies transmitted from mother to baby.
2. Artificial - antibodies transfused or injected into an individual.
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What is a vaccination?
Vaccination involves the introduction of a pathogen's antigens into the body, usually via injection. This stimulates the body to produce an immune response to the pathogen and in doing so, allows the body to develop artificial active immunity. In order to produce an immune response, vaccines (the injected substance) usually contain antigens. However, they also need to be safe to prevent symptoms of the disease.
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What may Vaccines contain?
- Dead or inactivated pathogens.
- Attenuated (weakened) pathogen strains.
- A harmless version of a toxin.
- Isolated antigens from a pathogen.
- Genetically engineered antigens.
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How does vaccination provide immunity?
Vaccination causes the body to produce antibodies against specific antigens.
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What are the main steps of vaccination?
1. The vaccine, containing antigens, is injected into the blood.
2. This stimulates the primary immune response to produce antibodies against the pathogen.
3. Memory cells, capable of recognising these antigens, are produced.
4. On second exposure to this pathogen, memory cells rapidly divide into plasma cells.
5. Plasma cells rapidly produce antibodies against the pathogen.
6. The pathogen is destroyed before any symptoms are experienced.
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What are the factors that affect how successful a vaccination programme will be?
1. Availability - Suitable vaccines must be affordable and available in large amounts for mass immunisation.
2. Minimal side effects - The fewer the side effects from the vaccine, the better the public acceptance.
3. Infrastructure - Necessary resources for producing, storing, and transporting the vaccine are essential, including advanced technology and refrigeration.
4. Administration - Proper and timely vaccine administration is important, requiring trained healthcare workers
5. Herd immunity - The goal is to vaccinate the majority of the population to achieve herd immunity.
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What is herd immunity?
Herd immunity arises when a sufficiently large proportion of the population has been vaccinated (and are therefore immune) which makes it difficult for a pathogen to spread within that population. Those who are not immunised are protected and unlikely to contract it as the levels of the disease are so low.
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What are the factors that may prevent the elimination of a disease?
1. Individual immunity failures - People with weak immune systems (babies, elderly people, and patients with compromised immune systems) may not be able to withstand vaccines, or may not develop an immune response.
2. Pre-immunity infection - Some individuals might contract the disease post-vaccination but before immunity develops, becoming potential disease reservoirs.
3. Pathogen mutation and antigenic variability - Rapid antigenic changes due to frequent mutations can make vaccines ineffective, as the immune system can no longer recognise the pathogen's new antigens (e.g. with diseases like influenza).
4. Pathogen variety - With diseases like the common cold, the sheer number of pathogen variants can make developing a universally effective vaccine nearly impossible.
5. Pathogen hiding - Certain pathogens can evade the immune system by 'hiding' inside cells or inhabiting hard-to-reach body regions like the intestines (e.g. with cholera).
6. Vaccine objections - Personal, religious, ethical, or medical objections to vaccination can hinder disease eradication. Misinformation can lead to reduced vaccination rates.
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What is antigen variability and what does it mean for vaccinations?
Some pathogens can change their antigens in a process known as antigenic variability. Antigenic variability makes it difficult to develop vaccines against some pathogens because if the antigens change enough they will no longer be recognised by the immune system. This means that memory cells produced from vaccination against one strain will not recognise the antigens from another strain. As a result, vaccines need to be changed frequently to provide protection against the most recent pathogenic strains.
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What is HIV?
HIV is a virus that weakens the immune system.
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What structures does the HIV virus contain?
1. Genetic material - Two single strands of RNA.
2. Enzymes - One of these enzymes is reverse transcriptase, which allows the virus to convert RNA into DNA.
3. Capsid - A layer of protein molecules that surrounds and protects the genetic material.
4. Envelope - An outer layer made up of phospholipids.
5. Glycoproteins - Also known as attachment proteins or envelope proteins, these help the virus to bind to host cells.
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How does HIV replicate?
As HIV is a virus, it cannot replicate itself and instead must use a host cell to produce new virus particles. HIV uses helper T cells as host cells, damaging the immune system of the infected individual.
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What are the steps in HIV replication?
1. Attachment proteins on the HIV attach to receptors on a helper T cell.
2. HIV releases its RNA into the helper T cell.
3. Reverse transcriptase converts this RNA into DNA.
4. The viral DNA is inserted into the helper T cell's genome.
5. The helper T cell's DNA is translated to make viral proteins.
6. The proteins are used to assemble new HIV particles.
7. Fully assembled HIV particles leave the cell in order to infect other cells.
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How does HIV infection progress leading to AIDS?
1. Transmission - HIV is transmitted via direct contact with bodily fluids (e.g. blood or sexual fluids) from an infected individual.
2. Acute infection- Once HIV enters the body, it rapidly replicates. This causes flu-like symptoms for 2 to 4 weeks.
3. Latency period - HIV replication drops to a low level for several years or decades. During this time, the individual usually experiences few or no symptoms. Antiretroviral therapy (ART) can prolong this stage for many years.
4. AIDS Development - After some years, HIV reactivates and destroys helper T cells. As the number of T cells in the body drops over time, the immune system begins to fail. At this point, we classify the person as having 'AIDS'.
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What does having AIDS mean for an individual?
Individuals with AIDS have a higher likelihood of developing various serious infections, and eventually, an opportunistic infection (e.g., pneumonia) can lead to death. AIDS also increases the risk of developing cancers.
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What is the treatment for HIV/AIDS?
HIV/AIDS is currently incurable. However, antiretroviral therapy (ART) can reduce viral replication to such low levels that most infected individuals don't experience any symptoms and can't transmit the virus.
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What are antibiotics?
Antibiotics are drugs that kill or inhibit the growth of bacteria. They target the bacterial enzymes and ribosomes used in metabolic reactions, meaning they do not damage human cells (as they contain different enzymes and ribosomes).
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Examples of how antibiotics affect bacteria include.
1. Preventing the synthesis of bacterial cell walls.
2. Disrupting protein activity in the cell membrane.
3. Disrupting enzyme action.
4. Preventing DNA synthesis.
5. Preventing protein synthesis.
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Why do antibiotics not work against viruses?
Antibiotics do not work against viruses because viruses lack cell structures, instead relying on host cells to carry out metabolic reactions. This means that antibiotics cannot target and disrupt these reactions. Furthermore, antibiotics are unable to reach viruses as they invade the organism's own cells.
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What is antibiotic resistance?
The increased use pf antibiotics has led to the development of antibiotic resistant bacteria which means that antibiotics that were once effective against these bacteria no longer work, making it much more difficult to treat bacterial infections.
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How does antibiotic resistance develop by natural selection?
1. Genetic mutations occur, making some bacteria resistant to an antibiotic.
2. When an infection is treated with antibiotics, resistant bacteria are able to survive.
3. Resistant bacteria reproduce, passing on the allele for antibiotic resistance to their offspring.
