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A Level Biology > Immune system > Flashcards

Immune system Flashcards

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1
Q

What is a pathogen?

A

microorganisms which cause disease

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2
Q

Give examples of pathogens?

A
  • Bacteria
  • Virus
  • Protist
  • Fungi
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3
Q

What are the two types of defence mechanisms?

A
  • Specific
  • Non-Specific
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4
Q

What is a non-specific defence mechanism?

A

Response is immediate and the same for all pathogens

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5
Q

What is a specific defence mechanism?

A

A slower response as it’s specific/targeted to each pathogen

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6
Q

What are two types of non-specific defence?

A
  • Physical and chemical barriers
  • Phagocytosis
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7
Q

Give an example of a physical/chemical barrier?

A
  • Hydrochloric acid in the stomach
  • Mucus and cilia in the trachea
  • Lysosomes in tears
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8
Q

What are the two types of specific defence mechanisms.?

A
  • Cell mediated response (T cells)
  • Hummoral response (B cells)
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9
Q

What is an antigen?

A

A molecule (often protein) that the body recognises as ‘foreign’ and so triggers an immune response.

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10
Q

What does the immune system have the ability to do?

A

Distinguish between self (body cells) and non-self cells (foreign materials)

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11
Q

How do autoimmune diseases occur?

A
  • If the immune system goes wrong it can begin to attack self cells causing autoimmune symptoms
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12
Q

Give an example of an autoimmune disease ?

A

Multiple Sclerosis
(Myelin Sheath of neurones are damaged)

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13
Q

How does the body distinguish between self and non-self cells?

A

Each type of cell has specific molecules (antigens) on its surface that identify it.
These molecules are usually proteins as their 3D tertiary structure enables unique identifiable structures to form on the surface

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14
Q

What are the non-self cells that trigger the immune response,?

A
  • Pathogens
  • Cells from other organisms of same species (transplants)
  • Abnormal body cells (tumours)
  • Toxins
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15
Q

What causes antigen variability?

A

Mutations of the DNA - which occurs in the genes coding for the antigen causes its tertiary structure to change shape

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16
Q

What does antigen variability mean for immunity?

A

Previous immunity is no longer effective as memory cells in the blood will only have a memory of old antigen shape

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17
Q

When are lymphocytes made?

A

Foetus

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18
Q

How are lymphocytes used to generate immunity as a foetus?

A

Lymphocytes complementary to the antigens on self-cells will die or production will be suppressed (This is to prevent your lymphocytes from attacking your own cells). The remaining lymphocytes are complementary to pathogenic and non-self cells.

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19
Q

After birth where are lymphocytes created?

A

Bone marrow

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20
Q

Describe the process of phagocytosis?

A
  • Chemicals are released by the pathogen
  • The phagocytes are attracted to these chemicals (foreign substances) and move towards the pathogen
  • The phagocyte engulfs the pathogen into a vesicle called a phagosome (by endocytosis)
  • Lysosomes found in the phagocyte move towards the vesicle and fuse with the phagosome
  • Lysozymes (hydrolytic enzymes) in the lysosomes digests the pathogen
  • The phagocyte displays the important antigens on its cell surface membrane
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21
Q

What is an antibody?

A

A protein with specific binding sites complementary to a specific antigen, synthesised and secreted by plasma cells.

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22
Q

What type of structure do antibodies have?

A

They are a Y - Shaped protein
Made up of 4 polypeptide chains held together by disulphide bridges
X2 heavy chains and x2 light chains

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23
Q

How does an ANTIGEN -ANTIBODY COMPLEX form?

A

When an antibody collided with a foreign cell that possess non-self antigens with a complementary shape, it binds with one of the antigens

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24
Q

What type of structure do antibodies have?

A

A specific 3D tertiary structure
The antigen binding sites are variable regions which are complementary to one specific antigen as they are made of a specific amino acid sequence

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25
Q

How do antibodies lead to the destruction of pathogens.?

A

Agglutination

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26
Q

What is agglutination?

A

Agglutination is when antibodies each bind to an antigen on two separate pathogens, causing the pathogens to clump together via a network of antigen-antibody complexes.
This clump is then easier for phagocytes to locate and engulf. The antibodies also serve as a marker for the phagocyte to commence phagocytosis of the bacteria.

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27
Q

What are MABs?

A

Monoclonal antibodies-antibodies with the same tertiary structure produced from a genetically identical set of plasma cells - antibodies are all specific to the same antigen

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28
Q

What type of lymphocyte does the cell mediated response use?

A

T Lymphocytes

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29
Q

What type of lymphocyte does the hummoral response use

A

B lymphocytes

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30
Q

Where are B and T cells produced?

A

Bone Marrow

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31
Q

Where do T cells mature?

A

Thymus gland

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32
Q

Approximately how many types of B/T cells are there?

A

~ 10 million

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33
Q

Explain the process of the cell mediated response?

A
  • The invading pathogen is engulfed by the phagocyte, the lysosomes within the phagocyte digest the pathogen in the phagosome and present its antigens on the cell surface membrane(becoming an APC - antigen presenting cell)
  • The T cell with a complementary surface receptors binds to the APC (clonal selection)
  • This stimulates/activates the T cells causing them to divide by mitosis and form clones
  • Some T cells become memory T cells
  • Some become Cytotoxic/Killer T cells which release cytotoxins to kill infected cells
  • Some become Suppressor T cells which release cytokines to stimulate phagocytosis
  • Some become Helper T cells which bind the the Antigen presenting B cells, which stimulates the B cells causing them to divide by mitosis (forming clones)
  • Some B cells become memory B cells whilst some become plasma cells which produce antibodies complementary to the antigen the B cell presents on its surface
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34
Q

What are the 4 different types of T cells which form?

A
  • Memory T cells
  • Suppressor T cells
  • Cytotoxic T cells
  • Helper T cells
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35
Q

How does the hummoral response work?

A
  • B cells with complementary surface antibodies bind to antigens in solution
  • The antigens are ingested and processed before being displayed on their cell surface membrane
  • Helper T cells bind to the antigen on the B cell surface stimualating B cells to divide by mitosis (forming clones)
  • These B cells then become memory B cells or Plasma cells which produce complementary antibodies to the antigens displayed on the B cell surface
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36
Q

What are the two types of B cells which form?

A
  • Memory B cells
  • Plasma cells (produces antibodies)
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37
Q

What are monoclonal antibodies?

A

Antibodies with identical tertiary structure produced by genetically identical plasma cells that are all specific to one antigen

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38
Q

How are MABs artificially produced?

A
  • A mouse is injected with a dead/attenuated antigen from a microorganism which triggers an immune response
  • The plasma cells are harvested from its liver
  • The plasma cells are fused with tumour cells to create a hybridoma cell - which divide uncontrollably and produce specific antibodies
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39
Q

What are the three different uses of MABs?

A
  • Targeting medication to specific cell types
  • Medical testing
  • Medical diagnosis using ELISA
40
Q

What are the two types of targeted medication for specific cells?

A
  • Direct Monoclonal Antibody Therapy
  • Indirect Monoclonal Antibody Therapy
41
Q

How does Direct MAB therapy work?

A
  • MABs are produced which are specific to the antigen on the target cell (eg. cancerous cell)
  • The antibodies are given to the patient and they bind to the antigen on the target cell
  • This prevents their uncontrolled growth by blocking growth signalling pathways
42
Q

What is Indirect MAB therapy?

A
  • A cytotoxic drug is attached to the monoclonal antibody
  • This antibody is given to the patient and binds to the complementary antigens on the surface of the target cell
  • The target cell is killed as the cytotoxin is released
43
Q

What are the practical application of Medical testing with MABs?

A

Pregnancy Testing
COVID

44
Q

What is the purpose of pregnancy tests ?

A

To detect the hormone HCG in the urine

45
Q

What are the three sites of a pregnancy test strip?

A
  • Reaction Site
  • Test Site
  • Control Site
46
Q

What happens at the reaction site of a pregnancy test strip?

A
  • It contains mobile anti-HCG antibodies (which are bound to an enzymes/coloured beads) that are complementary to the HCG hormone (protein)
  • If the HCG hormone is present it will bind to the anti-HCG antibody at the binding site
47
Q

How does urine move up the test strip?

A

By capillary action

48
Q

What happens at the test site of a pregnancy test strip?

A
  • Contains fixed/immobilised anti-HCG antibodies and dye molecules
  • The anti-HCG antibody binds to the HCG portion of the antigen-antibody complex
  • The enzymes linked to the antibody catalyse a reaction with the dye molecules (substrate) and form a coloured product when the E-S complex forms
49
Q

What happens at the control site of pregnancy tests?

A
  • Fixed/immobile anti-mouse antibodies
  • Anti-HCG antibodies (become antigens) that didn’t bind at the test site bind to anti mouse antibodies and cause a coloured product to form
50
Q

What is the purpose of the control site?

A

Prove the test has worked/ been successful

51
Q

What does ELISA stand for?

A

Enzyme Linked Immunosorbent Assay

52
Q

What is the purpose of ELISA?

A

A lab technique used to identify the presence and concentration of an antigen or antibody in a patient sample

53
Q

What are the two types of ELISA?

A
  • Direct ELISA
  • Indirect ELISA
54
Q

Give a brief overview of what the two types of ELISA are?

A

Direct - Antibody bound to multi-well plate
Indirect - Antigen bound to multi- well plate

55
Q

Explain how the ELISA test works for HIV diagnoses?

A
  • HIV antigen molecules attached to the walls of the multi-well plate
  • Add sample of blood plasma to well, if the HIV antibody is present they will bind to the HIV antigen
  • Wash out excess antibodies which haven’t bound to the antigens in the multi-well plate
  • Add a second antibody with an enzyme attached to, this binds specifically to the HIV antibody (if present)
  • Well is washed again to remove excess secondary antibody
  • A yellow solution is added which changes blue if the enzyme is present
  • The blue colour indicates HIV antibodies are present and the person is HIV positive
56
Q

What does a higher colour intensity indicate in an ELISA test?

A

A higher concentration of antigen/antibody

57
Q

What control should be used when doing an ELISA test?

A
  • Complete test with a salt solution not blood plasma
58
Q

Why should you do a control experiment for ELISA?

A
  • To ensure the only thing causing the colour change is the enzyme
  • Washing out is effective
59
Q

Ethical issues associated with MABs?

A

Mice used to produce tumours for antibody production
Informed consent from patients as some deaths linked to use
Clinical trials have significant risks

60
Q

What do vaccines contain?

A

They contain dead/attenuated antigens of specific microorganisms that induce a primary immune response (producing memory cells) without suffering the symptoms of the disease

61
Q

What is a primary immune response?

A

The first encounter/exposure to a specific antigen

62
Q

What is a secondary immune response?

A

The second exposure to a specific antigen
Trigger the production of more antibodies more quickly

63
Q

How do vaccines work?

A
  • A dead/attenuated antigen from a specific pathogen is inserted into the human body
  • Phagocytosis occurs and present the antigens on its cell surface membrane
  • Antigens are processed and displayed on antigen presenting B cells (APC)
  • The B cell is activated by the T helper cell resulting in mitosis
  • This forms clones of memory cells and plasma cells (produce complementary antibodies)
  • The memory cells provide long lasting immunity and is ready for antigen to enter the body again
64
Q

What is herd immunity?

A

When a sufficiently large proportion of the population has been vaccinated to make it difficult for a pathogen to spread within that population

65
Q

Why can’t vaccines eliminate disease?

A
  • Certain individuals have defective immune systems
  • Certain pathogens ‘hide’ from the immune system
  • May have religious, medical or ethical obligations
  • Antigenic variability
66
Q

What is antigenic variability?

A

The DNA of pathogens mutate frequently causing changes in the gene sequence causing the shape of the antigen to change and memory cells no longer able to recognise the antigen

67
Q

What is the difference between antigenic drift and shift?

A

Antigenic ‘drift’ gradual alteration (poor immune recognition)
Antigenic ‘shift’ significant alteration in shape (no immunity, no recognition)

68
Q

What are the ethical consideration for a vaccine?

A

Economically viable
Enough cover population in order to obtain herd immunity where possible
Produce, store and transport efficiently and without damage
Organised administration with trained staff

69
Q

What are the 4 types of immunity?

A

Passive
Active
Artificial
Natural

70
Q

What is passive immunity?

A

Introducing or inserting MAB into an organism from an outside source - no contact with the pathogen or its antigens

71
Q

Give an example of passive immunity?

A
  • Blood transfusions
  • Maternal antibodies from breast milk
72
Q

What is active immunity?

A
  • Involves direct contact with the pathogen/its antigens stimulating the body’s immune system to produce its own antibodies
73
Q

Give an example of active immunity?

A
  • Vaccines
  • Coming into contact with the pathogen
74
Q

Compare the differences between active and passive immunity?

A

Active
- produce antibodies via plasma cells
- involves memory cells
- longer term protection due to memory cells
- takes longer to develop/create

Passive
- Antibodies introduced into body from outside
- Short-term no memory cells made and antibodies break down
- Short-term

75
Q

Describe a successful vaccination?

A
  • Financially available
  • Few/no side effects
  • Sustainable way of producing, storing and transporting
  • Ways of administering it properly
  • Sufficient quantities to vaccinate (for herd immunity)
76
Q

What does HIV stand for?

A

Human Immunodeficiency Virus

77
Q

Describe the structure of an HIV virus?

A
  • Lipid envelope
  • Attachment proteins
  • Capsid
  • Genetic material (RNA)
  • Reverse transcriptase
78
Q

What is a retrovirus?

A

A group of viruses where the virus is able to insert its genetic material into a host cells DNA using enzyme reverse transcriptase

79
Q

What cell does HIV target and why?

A

It targets T helper cells
- Because it is a virus (acellular) it requires a host cell to reproduce

80
Q

Explain how HIV replicates ?

A
  • Virus binds (using attachment proteins) to receptor proteins (CD4) on the surface of helper T cell
  • Virus lipid envelope fuses with the cell surface membrane
  • The capsid breaks down and releases the genetic material (RNA) and enzymes into the cell
  • Reverse transcriptase converts RNA to DNA
  • The viral DNA moves into the nucleus via a nuclear pore and is inserted into the host cell
  • The HIV DNA is transcribed into mRNA and translated into viral proteins
  • New viral particles assembled and bud off from the cell surface membrane to infect more cells (destroying the helper T cell)
81
Q

When is the AIDs diagnosis given to a patient?

A

When the helper T cell count drops below 200 cells/mm3 of blood when the normal level in 800-1200 cells/mm3

82
Q

What are AIDs symptoms related to?

A

Infections (usually secondary) the immune system is unable to deal with as they’re unable to produce an adequate immune response

83
Q

After being infected with HIV, the individual develops a number of other infections over the following years. Explain why?

A
  • HIV utilises helper t cell and as it replicates it destroys them
  • This leads to a decrease in the number of helper T cells in the blood
  • This means fewer helper T cells to activate B cells, which divide by mitosis to form clones of plasma and memory cells
  • Less/fewer antibodies against pathogens are available to fight secondary infections, so the immune system is unable to fight off pathogens
84
Q

What is the purpose of the aseptic technique of working close to a Bunsen flame ?

A

Allows for upward convection currents to sterilise the air

85
Q

What is the purpose of the aseptic technique of opening the petri-dish as little as possible ?

A

Prevent bacteria in the dish getting out and bacteria in the air contaminating the plate

86
Q

What is the purpose of the aseptic technique of washing hands with soap?

A

Prevent contamination form bacteria on hands

87
Q

What is the purpose of the aseptic technique of using a sterile pipettes/flaming bottle necks and glass spreader?

A

Maintain a pure culture of bacteria

88
Q

What is the purpose of the aseptic technique of disinfecting surfaces?

A

Kill bacteria on surfaces so contamination doesn’t occur

89
Q

What is the purpose of the aseptic technique of soaking contaminated pipettes tips in disinfectant?

A

To kill bacteria and prevent spreading outside the laboratory

90
Q

Why do some antibiotics create a larger zone of inhibition?

A
  • They are more effective in killing the bacteria
  • Diffuse more quickly through the agar
91
Q

If there is no zone of inhibition what can we conclude about the bacteria?

A

The bacteria has antibiotic resistance

92
Q

What are two statistical tests?

A
  • Standard Deviation
  • T-test
93
Q

How do you write a null hypothesis for a t-test?

A

There will be NO statistically significant difference between the mean… and any difference is due to chance

94
Q

How do you write a alternative hypothesis for a t-test

A

There will be a statistically significant difference between the mean… and any difference is not due to chance

95
Q

What is the minimum confidence % required for a statistically significant difference?

A

95%

96
Q

What is the ideal p value for t-tests?

A

P = 0.05
(5%) - could be due to chance

A Level Biology (19 decks)

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