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Biology A1 & A2 > 2C: Cell recognition & immunity > Flashcards

2C: Cell recognition & immunity Flashcards

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1
Q

What is an antigen?

A

Any part of an organism (often a protein on the surface of a cell) that is recognised as foreign by our immune system.
Antigens are genetically controlled - close relatives share similar antigens (useful for transplants)

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2
Q

Describe non- specific defences. Give examples

A
  • In all animals
  • Immediate
  • All the same
  • E.g: physical barrier (skin), phagocytes
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3
Q

Describe specific defences. Give examples

A
  • Only in vertebrates
  • Slower
  • Specific
    E.g: Cell-mediated responses, humoral response
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4
Q

Describe how the skin acts as a barrier to infection

A

The skin is a physical barrier that pathogens find it difficult to penetrate

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5
Q

Describe how Hydrochloric acid acts as a barrier to infection

A

HCL denatures the enzymes or coat proteins of most pathogens that enter the stomach

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6
Q

Describe how Epithelial mucus acts as a barrier to infection

A

Epithelial layers inside the body produce mucus that pathogens stick to and become immobilised

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7
Q

What is a phagosome?

A

Where pathogens are broken down in a phagocyte, pathogens are transported via vesicles

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8
Q

What is a lysozyme?

A

Enzymes found in lysosomes that break down the pathogen when it is fused to the phagosome.

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9
Q

How many polypeptide chains are antibodies made from?

A

4: 2 heavy, 2 light

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10
Q

What bond/ bridge joins the two heavy chains together in antibodies?

A

Disulfide bonds/ bridge

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11
Q

What shape is an antibody?

A

Y shaped structure

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12
Q

What is the stem in an antibody part of?

A

The constant region

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13
Q

What region are the ends of the arms in antibodies?

A

The variable regions that bind to the antigen

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14
Q

T lymphocytes.

  • Where are they matured?
  • Which type of immunity are they part of?
  • What do they have on their surface?
  • What are the 2 forms?
A
  • Matured in the Thymus gland
  • Part of cell mediated immunity
  • T cells have receptor proteins on their surface
  • 2 forms: Helper T cells (TH cells)
    Cytotoxic T cells (TC cells)
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15
Q

Describe the role of the receptor proteins T cells have on their surface.

A

The receptor proteins can detect and bind to one specific antigen.

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16
Q

What happens to the pathogens antigens when phagocytes destroy them?

What does this make it?

A

When the pathogen is engulfed by the phagocyte, the phagocyte presents the pathogens antigens on its cell membrane.

Making it a antigen presenting cell

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17
Q

Describe the cell mediated immune response. (4 stages)

A
  1. Phagocytosis occurs (phagocyte becomes an antigen-presenting cell)
  2. Protein receptors on TH cells bind to presented antigens
  3. This activates the TH cell
  4. The TH cell does the following:
    - divides by mitosis (= more TH cells)
    - Stimulate phagocytosis
    - Release cytokines to activate Tc cells
    - Activate B cells
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18
Q

Describe humoural mediated immunity. (4 stages)

A
  1. B cell with pathogen-specific antibodies engulf pathogens = becomes an antigen presenting cell
  2. TH cell bind to presented antigens on the B cell (clonal selection)
  3. B-cell becomes activated & divides by mitosis to form either:
    (Primary) Plasma cell –> produces antibodies
    (Secondary) Memory cell –> circulates in blood
  4. Antibodies produced attach to antigens and either:
    - Agglutinate (stick together) pathogens
    - Prevent pathogens invading body cells
    - Bind to free toxin proteins (which kill pathogen)
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19
Q

How are monoclonal antibodies produced?

A

From a single group of genetically identical B-cells (plasma cells) specific to one type of antigen.

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20
Q

How are monoclonal antibodies all identical in structure?

A
  • They have the same primary structure as they are coded for by the same genes.
  • So have the same secondary + tertiary structure as a result.
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21
Q

How are monoclonal antibodies produced? (3 steps)

A
  1. The specific antigen binds to the receptor on the B cell
  2. A helper T cell sends out a chemical signal to activate B cells which then releases specific antibodies
  3. Thus by using the same plasma cells, identical antibodies will be produced
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22
Q

What are the two types of immunity?

A

Cell mediated and humoral

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23
Q

How do monoclonal antibodies use targeting drugs?

A
  • The MAs have the same unique tertiary structure
  • Therefore, they bind to a specific antigen with a complementary shape
  • Therefore, you can make monoclonal antibodies bind to a specific target molecules e.g cell antigen
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24
Q

What are two treatments using monoclonal antibodies?

A

Cancer treatment and pregnancy tests

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25
Q

In cancer treatments, what does the monoclonal antibody bind to?

A
  • Tumour markers (cancer cells unique antigens)

- Anti cancer drugs can be attached to the antibodies

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26
Q

In cancer treatments, how do the monoclonal antibodies work?

A
  • Anti cancer drug attached to the antibodies which will only be released where antibody binding occurs i.e at cancer cells
  • This reduces side effects
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27
Q

In pregnancy tests, what is the monoclonal antibody binding to?

A
  • The placenta produces HCG, which is found in the urine of pregnant women
  • HCG will bind to the antibodies
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28
Q

In pregnancy tests, how do the monoclonal antibodies work?

A

The HCG antibody -colour- complex moves along the strip until it binds to a different (immobilised) antibody that is also complementary to HCG.

The antibodies accumulate = coloured line (blue if HCG is present)

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29
Q

What are the ethical issues involved with monoclonal antibodies?

A
  • Production involves mice, they are injected with tumour cells = deliberately inducing cancer in mice
  • Positive results in treating cancer + diabetes but negative results involving deaths in treating multiple sclerosis!
  • Testing for new drugs can be dangerous. e.g in march 2006, 6 healthy volunteers trailed MAs and within minutes suffered multiple organ failure.
30
Q

What is the primary immune response?

A
  • Happens when a new pathogen first invades
  • Relatively few initial specific T and B cells
  • Relatively few clones produced
  • Symptoms are visible
31
Q

Describe the secondary immune response.

A
  • Happens when the same pathogen infects for a second time
  • Memory cells are present + ready to respond to a second infection (weeks/ month/ years later)
  • Much faster response to reinfection:
    Memory T cells divide into cytotoxic cells
    memory B cells divide into plasma cells
  • Many more T and B cells produced = stronger response
  • Pathogen destroyed before it can cause symptoms
32
Q

What are memory cells?

A
  • Some of the activated TH and B cells differentiate into memory cells
  • These remain in the blood for a number of years.
33
Q

Describe Active Immunity

A
  • Produced by stimulating the production of antibodies using the individuals own immune system
  • Involves direct contact with the pathogen or its antigen
  • 2 types of active immunity: artificial and natural
34
Q

Describe Passive Immunity

Give 2 examples

A
  • Produced by the introduction of antibodies from an outside source
  • NO direct contact with pathogen or its antigens
  • Immunity acquired immediately
  • As the antibodies are NOT produced by the person there is no lasting immunity (no memory cells etc.

Examples:

  • Anti-venom given to snake bite victims
  • Immunity acquired by the fetus (antibodies transferred from the placenta)
35
Q

What do vaccines contain?

A

Vaccines contain dead/ weakened pathogens:

These do not cause disease but do contain the antigens necessary to elicit a primary immune response = immunity

36
Q

What are the 2 types of active immunity?

A

Natural and artificial

37
Q

Describe Natural Active immunity

A
  • Results from an individual becoming infected with the disease under normal circumstances
  • The body produces its own antibodies and may do so for many years
38
Q

Describe Artificial Active immunity

A
  • Forms the basis of vaccination (immunisation)

- Involves inducing an immune response, without them suffering symptoms of the disease

39
Q

What is herd immunity?

A

If enough people are immune to a pathogen (>90%) then the remaining people are often protected.
- This is due to the lack of hosts for the pathogen to reproduce in

40
Q

What is one feature of a successful vaccine? (side-effects)

A

Little/ no side effects. Unpleasant side-effects may discourage individuals from being vaccinated

41
Q

What is one feature of a successful vaccine? (availability)

A

It must be economically available in sufficient quantities to immunise most of the vulnerable population

42
Q

What is one feature of a successful vaccine? (producing, storing etc.)

A
  • Means of producing, storing and transporting the vaccine must be available.
  • Usually involves technologically advanced equipment, hygienic conditions and refrigerated transport
43
Q

What is one feature of a successful vaccine? (administration)

A

There must be a way to administer the vaccine properly and at the appropriate time
- Involves training staff with the right skills throughout the population

44
Q

Describe the structure of the HIV virus.

How is it different to a regular virus?

A
  • Attachment proteins
  • Lipid envelope
  • Matrix
  • Capsid
    Differences:
  • Genetic material is RNA
  • Enzymes are reverse transcriptase
45
Q

What does HIV stand for?

A

Human Immunodeficiency Virus

46
Q

Are antibodies made during reinfection active or passive immunity?

A

Passive

47
Q

Why does the flu vaccine have to change every year?

A

Antigenic variability

48
Q

Describe antigenic variability

A
  • Pathogens mutate frequently so their antigens can change dramatically
  • This means that vaccines can suddenly become ineffective because the new antigens are not recognised by the immune system, which means that the pathogens are not detected and destroyed
49
Q

What is an example of antigenic variability?

A

The influenza virus - which changes its antigens frequently

50
Q

How is HIV spread?

A

Exchanging bodily fluids:

  • Sexual contact
  • Sharing needles
  • Breast milk
51
Q

Describe the process of HIV replication (8 stages)

A
  1. HIV infects + circulates in the blood
  2. Protein on HIV binds to protein on cell surfaces called CD4 (usually T helper cells)
  3. Capsid fuses with cell surface membrane, RNA and enzymes of HIV enter the cell
  4. HIV reverse transcriptase (enzyme) converts virus RNA to DNA
  5. DNA moved into cells nucleus
  6. mRNA made to encode new viral proteins
  7. mRNA passes out of the nucleus and uses cell protein synthesis mechanisms to make new HIV particles
  8. HIV particles break away with a piece of the cell membrane which forms the lipid envelope (avoids detection from the immune system)
52
Q

Describe AIDs

A
  • HIV kills or interferes with normal functioning of the immune system, leading to AIDS
  • AIDS sufferers have around 200mm-3 T helper cells circulating, compared with around 1000mm-3 in a healthy person
  • AIDS sufferers will develop small infections a lot quicker and they will be a lot more deadly to the sufferer
  • Usually HIV/AIDS does not kill a person, but the ill health associated with it does
53
Q

What does AIDS stand for?

A

Acquired Immune Deficiency Syndrome

54
Q

What does metastasize mean?

A

Cancer has spread to other sites in the body by metastasis.

55
Q

How might a vaccine fail to eliminate a disease in certain people?

A

Due to an individual’s defective immune system

56
Q

How might a vaccine not eliminate a disease after it is administered?

A

Individuals may develop the disease immediately after vaccination but before their immune levels are high enough to prevent it. These people may harbor the pathogen and reinfect others

57
Q

How does the fact that pathogens frequently mutate mean that vaccines become ineffective?

A
  • The pathogen may mutate frequently so its antigens change suddenly rather than gradually
    = antigenic variability
  • Resulting in vaccines suddenly becoming ineffective because the antibodies they produce are no longer complementary to the pathogens antigens.
58
Q

Describe the process of phagocytosis

A
  1. Phagocyte is attracted to the pathogen by chemicals, it moves towards the pathogen along a conc. gradient
  2. The phagocyte binds to the pathogen & engulfs it
  3. The phagosome and the lysosome fuse together, lysozymes digest the pathogen.
  4. The phagocyte presents the pathogens antigens = making it an antigen presenting cell
59
Q

In which response does phagocytosis happen?

A

T- lymphocyte response/ cell mediated immunity

60
Q

Define an antibody

A

An antibody is a protein produced by lymphocytes in the presence of a specific, usually foreign, antigen

61
Q

Describe the 2 different types of lymphocyte.

A 
B cells:
- Humoral immunity 
- Divide into memory/ plasma cells 
T cells:
- Cell mediated immunity 
- Cytotoxic (Tc) cells + helper (Th) cells
62
Q

What is the role of antigen presenting cells in the cellular response?

A
  • Protein receptors on the Th cells bond to the presented antigens = which activates Th cells
  • Allows the body to identify foreign objects as pathogens
63
Q

What is the ELISA test?

A
  • Medical diagnosis tool

- Uses monoclonal antibodies

64
Q

How is the ELISA test used in HIV testing?

A
  1. HIV antigens are attached to plate/ well (these antigens are SPECIFIC & will only bind to a certain antibody) then patients blood is added to plate
  2. If HIV is present the patient will have monoclonal antibodies complementary to the HIV antigen, then these antibodies will bind to the antigen. plate washed to remove unattached antibodies
  3. Then another monoclonal antibody with an enzyme bound to it is injected into the plate, this will only attach if the HIV antibodies are present (if patient is HIV positive). The plate is washed to remove unattached antibodies (otherwise would always show positive)
  4. Colourless substrate is added to the plate, if enzyme is present the subrate will react with it and turn into a coloured molecule
65
Q

Describe how activated Tc cells cause the death of a pathogen.

A

Activated Tc cells:
- Produce perforin protein
- This makes holes in cell surface membranes
= results in cell DEATH

66
Q

Describe plasma cells, which immune response are they part of?

A

They secrete large amounts of antibodies, they are part of the primary immune response

67
Q

Describe memory cells, which immune response are they part of?

A

They have pathogen specific antigens and circulate in the blood ready for later reinfection. They are part of the secondary immune response

68
Q

Which immune response are B cells part of?

A

Humoral

69
Q

Which immune response are T cells part of?

A

Cell mediated

70
Q

Which immune response involves phagocytes?

A

Cell mediated

Biology A1 & A2 (19 decks)

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