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AS/A-Level Biology > CELLS: The Immune System COPY > Flashcards

CELLS: The Immune System COPY Flashcards

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1
Q

What are antigens?

A

Molecules that can generate an immune response when detected by the body.

They are usually proteins.

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2
Q

Where are antigens usually found?

What can they be used to identify?

A

Usually found on the surface of a cell.

Used by immune system to identify:

  • Pathogens
  • Abnormal body cells
  • Toxins
  • Individuals of the same species (organ transplants)
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3
Q

What are pathogens?

A

Microorganisms that cause disease.

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4
Q

What is a phagocyte?

A

A type of white blood cell that carries out phagocytosis.

They are the first cell to respond to an immune system trigger inside the body.

Some travel in the blood but can move out of the blood vessels into other tissues.

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5
Q

What is phagocytosis?

A

The process of pathogens being engulfed by phagocytes in the immune system.

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6
Q

Describe the process of phagocytosis:

A
  • Chemical products of pathogens act as attractants, causing phagocytes to move towards the pathogen.
  • Receptors on the phagocyte recognise and attach to the antigens on a pathogen.
  • Cytoplasm of the phagocyte moves round the pathogen, engulfing it.
  • Pathogen is now contained in phagocytic vacuole/phagosome in the cytoplasm of the phagocyte.
  • Lysosome fuses with the phagocytic vacuole.
  • Released lysozymes destroy ingested bacteria by hydrolysis of their cell walls.
  • Soluble products of pathogen are absorbed into the cytoplasm.
  • Phagocyte then becomes antigen-presenting activating other immune system cells.
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7
Q

The presence of an antigen does what?

A

Triggers the production of an antibody as part of the body’s defence system.

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8
Q

What type of immune responses can the body have?

Give examples.

A
  • Non-specific, eg. phagocytosis which occurs whatever the infection.
  • Specific, eg cell-mediated and humoral immunity which uses specific lymphocytes.
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9
Q

What is a benefit of specific immune responses?

A

Whilst they can be slower in action at first, they often provide long-term immunity.

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10
Q

What are lymphocytes?

A

White blood cells, used in specific immune resonses, that are produced by stem cells in the bone marrow.

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11
Q

What are the two types of lymphocytes?

A
  • B lymphocytes - mature in the bone marrow.
  • T lymphocytes - mature in the thymus gland (in the chest, between the lungs).
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12
Q

What type of immunity are T cells associated with?

A

Cell-mediated immunity.

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13
Q

What type of immunity are B cells associated with?

A

Humoral immunity.

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14
Q

What are the different types of T cells?

What is the function of each?

A
  • Helper T-cells - release chemical signals that activate and stimulate phagocytes. Also activate B-cells which secrete antibodies.
  • Cytotoxic T-cells - kill abnormal and foreign cells.
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15
Q

How does a T cell become activated?

A

Receptor proteins on its surface bind to complementary antigens presented by phagocytes.

Receptor proteins are only specific to one type of antigen and therefore there is a vast number of different types of T cells.

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16
Q

Why is the work done by T cells known as cell-mediated immunity?

A

Because T lymphocytes will only respond to antigens that are presented on a body cell, not just antigens within the body fluids.

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17
Q

Describe cell-mediated immunity:

A
  1. Pathogens invade body cells or are taken in by phagocytes.
  2. Phagocyte becomes antigen-presenting.
  3. Receptors on a specific helper-T cell are complementary to this antigen.
  4. This attachment activates the T cell to divide by mitosis and form a clone of genetically identical cells.
  5. Cloned T cells:
    1. Develop into memory cells
    2. Stimulate phagocytes to engulf pathogens by phagocytosis
    3. Stimulate B cells to divide and secrete antibodies
    4. Activate cytotoxic T cells, which kill the pathogen.
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18
Q

How to cytotoxic T cells kill infected cells?

A
  • Produce a protein called perforin that makes holes in the cell-surface membrane.
  • Holes mean the cell membrane becomes freely permeable to all substances.
  • The cell dies.
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19
Q

What are B cells?

A

White blood cells that are covered with specific antibodies

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20
Q

Describe the process of humoral immunity:

A
  1. Surface antigens of an invading pathogen are taken up by a B cell.
  2. B cell processes the antigens and becomes antigen-presenting.
  3. Helper T cells attach to processed antigens on B cell and activate the B cell - this is known as clonal selection.
  4. B cell is activated to divide by mitosis to give a clone of plasma cells.
  5. Cloned plasma cells produce and secrete specific antibodies.
  6. Antibody attaches to antigens on pathogen and destroys them.

Some B cells develop into memory cells, which respond to future infections by the same pathogen.

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21
Q

What forms when antibodies bind to antigens?

A

Antigen-antibody complex.

22
Q

What is clonal selection?

A

A process proposed to explain how a single B or T cell that recognizes an antigen that enters the body is selected from the pre-existing cell pool of antigen and then reproduced to generate a clonal cell population that eliminates the antigen.

23
Q

What are plasma cells?

A

Cells identical to B cells (clones of B cells), that secrete antibodies specific to the antigen.

24
Q

What type of antibodies do plasma cells secrete?

A

Monoclonal antibodies.

25
Q

What are antibodies made of?

A

Four polypeptide chains; two heavy chains and two light chains.

26
Q

Draw and label an antibody:

A
27
Q

Why does an antibody have two binding sites?

A

So it can bind to two pathogens at once.

28
Q

What does the constant region of an antibody bind to?

A

Receptors on cells such as B cells.

29
Q

What type of molecule are antibodies?

A

Proteins - made of specific chains of amino acids.

30
Q

The specificity of an antibody depends on what?

A

The variable regions, which form antigen binding sites.

These have unique tertiary structure (due to different amino acid sequences) and are only complementary to one specific antigen.

31
Q

What is the same for all antibodies?

A

The constant region.

32
Q

What is important to understand about antibodies?

A

They do not destroy pathogens themself but rather prepare the antigen for destruction.

33
Q

What is agglutination?

A

The immune response which involves antigens clumping together.

34
Q

Give an example of how antibodies assist in the destruction of pathogens:

A

Bacterial cells

  • Cause agglutination of the cells.
  • This clumps the cells together making them more easily located by phagocytes as they are less spread out in the body.
  • Then, serve as markers to stimulate phagocytes to phagocytose the bacterial cells attached to them.
35
Q

Describe the primary immune response:

A
  • Slow as there aren’t many B-cells that can make the antibody needed to bind to it.
  • Person will therefore show symptoms.
  • T and B cells produce memory cells, that remain in the body for a long time.
  • Person is now immune and can respond quickly to a second infection of same pathogen.
36
Q

What is the primary immune response?

A

The response from the immune system when an antigen enters the body for the first time.

37
Q

What does each type of memory cell remember?

A
  • Memory T cells remember the specific antigen and will recognise it the second time around.
  • Memory B cells remember the specific antibodies needed to bind the antigen.
38
Q

What is the secondary immune response?

A

When a pathogen already known to the immune system re-enters the body, the immune system produces a quicker, stronger immune response.

39
Q

Describe secondary immunity:

A
  • Clonal selection happens faster.
  • Memory B cells activate and divide into plasma cells that secrete correct antibody.
  • Memory T cells activate and divide into correct type of T cell to kill the cell carrying the antigen.
  • The pathogen is often killed before people start to show symptoms.
40
Q

Draw a diagram illustrating the defence mechanisms of the body:

A
41
Q

How do lymphocytes only respond to foreign cells and not self-cells in fetuses?

A
  • Lymphocytes constantly collide with body cells.
  • Some of these lymphocytes will have receptors that exactly fir those of the body’s cells.
  • The lymphocytes either die or are suppressed.
  • So then only lymphocytes left are those that fir non-self cells.
42
Q

In adults, why do lymphocytes only respond to foreign cells and not self-cells?

A
  • Lymphocytes produced in bone marrow initially only encounter self-antigens.
  • Any lymphocytes that are specific to these self cells undergo apoptosis, before they can differentiate into mature lymphotcytes.
  • No clones of these anti-self lymphocytes appear in the blood, leaving only those that respond to non-self cells.
43
Q

What is apoptosis?

A

Programmed cell death.

44
Q

The antibodies secreted by plasma cells are known as what?

A

Monoclonal antibodies.

45
Q

What is immunity?

A

When an individual’s immune system is better prepared for a secondary infection and can kill it before it causes any harm.

46
Q

Describe non-specific defence mechanisms:

A
  • Skin forming physical barrier - stopping the entry of pathogens.
  • Phagocytosis.
47
Q

Describe specific defence mechanisms:

A
  • Cell - mediated responses involving T lymphocytes.
  • Humoral responses involving B lymphocytes.
48
Q

To defend the body from invasion, lymphocytes must be able to do what?

How do they do this?

A

They must be able to distinguish the body’s own cells and molecules from those that are foreign.

They do this by recognising the 3D, specific tertiary structure of the cell - antigens.

49
Q

What are negative implications of the immune system?

A

The immune system recognises donor tissues or organs as non-self and so attempts to destroy transplants.

50
Q

How can the effect of tissue rejection be minimised?

A
  • Transplants need to be matched as closely as possible to the recipient.
    • Best matches often come from gentically close relatives.
  • Immunosuppressant drugs are often administered to reduce the level of immune response that still occurs.

AS/A-Level Biology (190 decks)

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