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Biology > 3.2.4 Cell recognition and the immune system > Flashcards

3.2.4 Cell recognition and the immune system Flashcards

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1
Q

what is an antigen?

A
  • a protein located on the surface of cells
  • generates an immune response
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2
Q

what do antigens enable the immune system to identify?

A
  • pathogens
  • cells from other organisms of the same species
  • abnormal body cells
  • toxins
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3
Q

what is a pathogen?

A

a microorganism which causes disease

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4
Q

how do lymphocytes distinguish between self and non-self cells?

A
  • each type of cell has specific molecules on its surface that identify it (antigen)
  • these molecules are usually proteins
  • their 3D tertiary structure enables lots of unique and identifiable shapes to be made
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5
Q

what is antigen variability?

A
  • pathogens’ DNA can mutate frequently
  • if a mutation occurs in the gene which codes for the antigen, then the shape of the antigen will change
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6
Q

what is the effect of antigen variability on disease and disease prevention?

A
  • any previous immunity to the pathogen with variable antigens is no longer effective
  • this is because the memory cells in the blood will have a memory of the old antigen shape
  • e.g., the influenza virus mutates and changes its antigen very quickly which is why a new flu vaccine has to be created each year
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7
Q

what are the two types of white blood cells?

A

phagocytes and lymphocytes

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8
Q

what are the two types of phagocytes?

A

neutrophils and macrophages

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9
Q

what are the two types of lymphocytes?

A

B lymphocytes and T lymphocytes

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10
Q

what is the difference between neutrophils and macrophages?

A

both engulf and digest pathogens, but macrophages can become antigen-presenting cells

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11
Q

what type of response is phagocytosis?

A
  • non-specific
  • any non-self cell that is detected will trigger the same response to destroy it
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12
Q

describe the process of phagocytosis in detail

A
  • phagocytes are in the blood and tissues and any chemicals/debris released by pathogens/abnormal cells attract the phagocytes
  • receptor binding points on phagocytes will attach to antigens on the pathogen
  • phagocyte changes shape to move around and engulf the pathogen
  • once engulfed, the pathogen is contained within a vesicle called a phagosome
  • a lysosome within the phagocyte will fuse with the phagosome and release its contents
  • lysozyme enzyme is released into the phagosome which hydrolyses the pathogen to destroy it
  • soluble products are absorbed and used by the phagocyte
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13
Q

describe how bacteria are destroyed by phagocytes (6 marks)

A
  • phagocyte recognises foreign antigen
  • pathogen engulfed
  • enclosed in phagosome
  • phagosome fuses with lysosome
  • lysosome contains enzymes
  • pathogen digested / molecules hydrolysed
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14
Q

what are antigen presenting cells (APCs)?

A

any cell that present a non-self antigen on their surface

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15
Q

what are 4 examples of antigen presenting cells?

A
  • infected body cells will present viral antigens on their surface
  • a macrophage which has engulfed and destroyed a pathogen will present the antigens on their surface
  • cells of a transplanted organ will have different shaped antigens on their surface compared to our self-cell antigens
  • cancer cells will have abnormal shaped self-cells
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16
Q

describe how phagocytosis of a pathogen leads to the presentation of its antigens

A
  • phagosome fuses with lysosome
  • pathogen destroyed by lysozymes
  • antigens from pathogen are displayed on the cell membrane
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17
Q

what is a cell-mediated response?

A

involves the response of T lymphocytes to a foreign antigen

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18
Q

why are T cell responses described as ‘cell-mediated’?

A

T cells only respond to antigens which are presented on APCs, and not antigens detached from cells and within body fluids such as the blood

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19
Q

what are the steps of the cell mediated response?

A
  • once a pathogen has been engulfed and destroyed by a phagocyte, the antigens are positioned on the cell surface to become an APC
  • helper T cells have receptors on their surface which can attach to the antigens on the APC
  • once attached, this activates the helper T cells to divide by mitosis to replicate and make large numbers of clones
  • cloned helper T cells differentiate into different cells
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20
Q

what 3 things can cloned T helper cells do?

A
  • some remain as T helper cells and activate B lymphocytes
  • some stimulate macrophages to perform more phagocytosis
  • some become memory cells for that shaped antigen
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21
Q

what is the purpose of cytotoxic T cells?

A

to destroy abnormal or infected cells

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22
Q

how do cytotoxic T cells work?

A
  • release a protein (perforin) which embeds in the cell surface membrane and makes a pore so that any substances can enter or leave
  • this causes cell death
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23
Q

what is the humoral response?

A

the response involving B cells and antibodies

24
Q

where are lymphocytes made?

A

all lymphocytes are made in the bone marrow and B cells mature there too

25
Q

what are the steps of the humoral response?

A
  • antigens in the blood collide with their complementary antibody on a B cell
  • the B cell takes in the antigen by endocytosis and then presents it on it’s cell surface membrane
  • this B cell then collides with a helper T cell receptor, which activates the B cell to go though clonal expansion and differentiation (clonal selection)
  • B cells undergo mitosis to make large numbers of cells, these differentiate into plasma cells or memory B cells
26
Q

what is the purpose of plasma cells?

A

to make antibodies as a part of the primary immune response

27
Q

what is the purpose of helper B cells?

A
  • to divide by mitosis and make plasma cells rapidly if they collide with an antigen they have previously encountered as a part of the secondary immune response
  • this results in large numbers of antibodies being produced so rapidly that the pathogen is destroyed before any symptoms can occur
28
Q

what is an antibody?

A
  • a protein specific to an antigen
  • produced by B cells / secreted by plasma cells
29
Q

describe the structure of an antibody

A
  • 4 polypeptide chains - 2 heavy and 2 light
  • each chain has a variable region and a constant region
  • the chains are connected by disulphide bridges
  • all antibodies have the same constant regions that
    allow them to bind to receptors on immune system
    cells
  • they have two variable regions which are the
    antigen binding sites so they will have a unique
    tertiary structure complementary to an antigen
  • one antibody can bind to two pathogens at once
30
Q

what is agglutination?

A
  • antibodies are flexible and can bind to multiple antigens to clump them together
  • this makes it easier for phagocytes to locate and destroy the pathogens
31
Q

describe and explain the role of antibodies in stimulating phagocytosis (2 marks)

A
  • bind to antigen
  • are markers
    OR
  • cause agglutination/clumping
  • attract phagocytes
32
Q

what is passive immunity?

A
  • antibodies which come from another organism are introduced into the body
  • no long-term immunity as no memory cells are formed
33
Q

what is natural passive immunity?

A

a baby gets antibodies through placenta and in breast milk

34
Q

what is artificial passive immunity?

A

you are injected with antibodies

35
Q

what is active immunity?

A

immunity created by your own immune system following exposure to the pathogen or its antigen

36
Q

what is natural active immunity?

A

creation of the body’s own antibodies and memory cells following infection

37
Q

what is artificial active immunity?

A

creation of antibodies and memory cells following the introduction of a weakened version of the pathogen or antigens (via a vaccine)

38
Q

describe the differences between active and passive immunity (6 marks)

A
  • active involves memory cells, passive does not
  • active involves the production of antibodies by plasma cells / memory cells
  • passive involves antibodies introduced into the body from outside
  • active is long-term, because antibodies are produced in response to antigen
  • passive short term, because the antibody given is broken down
  • active can take time to develop / work and passive is fast acting
39
Q

what are vaccines?

A

small amounts of weakened or dead pathogen, or antigens are administered orally / by injection

40
Q

how do vaccines work?

A

exposure to antigens activates the humoral response

41
Q

describe how B cells respond to a vaccine (4 marks)

A
  • B cell binds to complementary antigen
  • B cell divides by mitosis
  • plasma cells produce antibodies
  • B cells develop into memory cells
42
Q

what is herd immunity?

A
  • if enough of the population are vaccinated the pathogen cannot spread easily amongst the populations
  • this provides protection for those who are not vaccinated
43
Q

what does HIV stand for?

A

human immunodeficiency virus

44
Q

what is the structure of HIV?

A
  • core = genetic material (RNA) and reverse transcriptase enzyme
  • capsid = outer protein coat
  • envelope = extra outer layer, made out of membrane taken from host cell’s membrane
  • protein attachments = on the exterior of the envelope, enables the virus to attach to the host’s T helper cells
45
Q

how does HIV replicate in cells (long)?

A
  • glycoprotein molecules on the virus surface bind to CD4 receptors on the surface of T helper cells
  • this allows the envelope surrounding the virus to fuse with the T helper cell membrane.
  • the capsid is released into the cell where it releases the RNA and reverse transcriptase
  • reverse transcriptase copies the viral RNA into a DNA copy
  • the DNA is inserted into the cell’s DNA which gets replicated when cells replicate
  • viral DNA is used to make HIV RNA and proteins at host ribosomes
  • viral particles are assembled which bud off from the cell membrane and go on to infect other cells
46
Q

how does HIV replicate in cells (short)?

A
  • attachment proteins attach to receptors on helper T cell
  • RNA and reverse transcriptase enter cell
  • RNA converted into DNA using reverse transcriptase
  • DNA inserted into host cell’s nucleus
  • DNA transcribed into HIV mRNA
  • HIV mRNA translated into new HIV proteins
  • virus particles assembled and released from the cell
47
Q

how does HIV affect the production of antibodies when AIDS develops in a person? (3 marks)

A
  • HIV destroys helper T cells
  • few B cells are activated
  • fewer antibodies are produced
48
Q

how does HIV cause the symptoms of AIDS?

A

acquired immunodeficiency syndrome (AIDS) is when the replicating viruses in the T helper cells interfere with their normal functioning of the immune system

49
Q

why are antibiotics ineffective against viruses?

A
  • virus replicate inside of cells, so it is difficult to destroy them without harming host cells
  • viruses also have different mechanisms to replicate and no cell wall, like bacteria, so cannot be destroyed by antibiotics
50
Q

how can inhibiting reverse transcriptase slow the development of AIDS?

A
  • stops new HIV particles from forming new HIV DNA
  • so slows the replication of HIV
  • stops the destruction of more T cells
  • so the immune system continues to work
  • this is how antiretroviral drugs work
51
Q

what is a monoclonal antibody?

A
  • antibodies with the same tertiary structure
    OR
  • antibodies produced from identical/cloned B cells
52
Q

what is direct monoclonal antibody therapy?

A
  • antibodies have a binding site which is complementary in shape to the antigens on the outside of cancer cells
  • antibodies are given to the patient and attach to cancer cells
  • this prevents the chemicals that enable uncontrolled cell division from binding to the cancer cells
  • therefore, monoclonal antibodies prevent the cancer cells growing
53
Q

what is indirect monoclonal antibody therapy?

A
  • monoclonal antibodies complementary in shape to the antigens on the outside of cancer cells have drugs attached to them
  • the cancer drugs are therefore delivered directly to the cancer cells and kill them
  • radioimmunotherapy is when radioactive isotopes are attached instead of drugs
54
Q

how do pregnancy tests work?

A
  • first contains a mobile antibody complementary to the antigen being tested for and has a coloured dye attached
  • mobile antibody moves to first window
  • first window has a second antibody which is complementary in shape to the antigen is immobilised
  • if antigen binds to first antibody, it will also bind to second antibody as they are both complementary to antigen
  • this means that dye stays in the first window
  • in the second window, a third antibody is immobilised which is complementary in shape to the first antibody
  • this means that first antibody binds to third antibody and dye stays in second window
  • 2 coloured lines = positive result
  • 1 coloured line in control window = negative result but test works
55
Q

how does an ELISA test work?

A
  • add the test sample from a patient to the base of the beaker
  • wash to remove any unbound test sample
  • add antibody complementary in shape to antigen being tested for
  • wash to remove any unbound antibody
  • add second antibody, which is complementary to first antibody and has an enzyme attached to it
  • second antibody binds to first antibody
  • wash to remove any unbound antibody
  • add substrate for enzyme, which is colourless
  • substrate produces coloured products in the presence of the enzyme
  • intensity of colour indicates the quantity of antigens present
56
Q

describe the role of antibodies in producing a positive result in an ELISA
test (4 marks)

A
  • the first antibody binds to the antigen which is complementary in shape
  • second antibody with an enzyme attached is added
  • the second antibody attaches to the first antibody (indirect ELISA)
  • substrate added and colour changes
57
Q

what is the ethical issue with monoclonal antibodies?

A

monoclonal antibody production requires mice to produce the antibodies, causes the death of animals

Biology (21 decks)

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