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Biology Year 1 > Topic 2C- Cells and the Immune System > Flashcards

Topic 2C- Cells and the Immune System Flashcards

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1
Q

What are antigens?

A

A protein found on the outside of cells that trigger an immune response

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2
Q

What things can antigens be used to identify?

A
  • pathogens
  • cells from other organisms of the same species
  • abnormal body cells (e.g. cancerous cells)
  • toxins
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3
Q

What are pathogens?

A

Microorganisms that cause disease e.g. virus

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4
Q

Where are phagocytes made?

A

In the bone marrow

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5
Q

What are the two types of phagocyte?

A

Neutrophils- engulf and digest pathogens
Macrophages- can punch holes in bacteria or stick proteins to the outside of the bacteria to make them more appealing for the neutrophils to destroy

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6
Q

Define phagocytosis

A

The cellular process of engulfing solid particles into the cell membrane- carried out by phagocytes.

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7
Q

Describe the steps of phagocytosis

A
  1. Pathogens recognised as having foreign/ non-self antigens. Pathogen attaches to the phagocyte by surface receptors
  2. The pathogen is engulfed by the phagocyte by endocytosis forming a phagosome
  3. The pathogen is now contained in a phagocytic vacuole in the cytoplasm of the phagocyte
  4. A lysosome fuses with the phagocytic vacuole. The lysozymes break down the pathogen.
  5. The phagocyte then presents the pathogen’s antigens- it sticks the antigens on its surface to activate other immune system cells.
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8
Q

What is an antibody?

A

Proteins which bind to antigens to form an antigen-antibody complex

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9
Q

Describe the antibody structure

A

4 polypeptide chains, 2 heavy, 2 light. each chain has a variable region and a constant region

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10
Q

Describe the importance of variable region of an antibody

A

They have a unique protein structure, which is tertiary, and complementary to an antigen.

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11
Q

What is the function of the constant region?

A

Allow binding to receptors on immune system cells. It is the same in all antibodies.

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12
Q

How do antibodies help clear up an infection? (3)

A

Agglutinating pathogens, neutralizing toxins, preventing the pathogen binding to human cells

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13
Q

How many variable regions does a binding site have?

A

two

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14
Q

What is a phagocyte?

A

A type of white blood cell that carries out phagocytosis.

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15
Q

What type of cells do phagocytes activate?

A

T-cells

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16
Q

What is a T-cell?

A

A type of white blood cell. It has receptor proteins on its surface that bind to complementary antigens presented to it by phagocytes. Different types of t-cells respond in different ways.

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17
Q

What do T-cells activate?

A

B-cells

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18
Q

What is a B-cell?

A

A type of white blood cell

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19
Q

What are B-cells covered with?

A

antibodies. each B-cell has different shaped antibodies on it’s membrane , so different ones bind to different shaped antigens.

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20
Q

What is clonal selection?

A

1) The antibody on the surface on the B-cell meets a complementary antigen and binds to it.
2) This, together with substances released from the helper T-cells, activates the B-cell
3) The activated B-cell divides into plasma cells

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21
Q

What are plasma cells?

A

They’re identical to the B-cell. They secrete loads of antibodies specific to the antigen. (monoclonal antibodies)

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22
Q

How many binding sites does an antibody have?

A

2

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23
Q

How does the number of binding sites an antibody has effect the pathogens?

A

2 binding sites means that two pathogens can bind at the same time. This means that the pathogens become clumped together, agglutination.

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24
Q

How does agglutination effect the phagocytes?

A

Phagocytes can bind to the antibodies and phagocytose many pathogens at once. This process leads to the destruction of pathogens carrying this antigen in the body.

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25
Q

What is the same for all antibodies?

A

the constant region

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26
Q

What are the two different types of immune responses?

A

cellular and humoral

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27
Q

What is cellular immune response?

A

the T-cells and other immune system cells that they react with

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28
Q

What is humoral immune response?

A

B-cells, clonal selection and the production of monoclonal antibodies form the humoral response.

29
Q

What is the primary immune response?

A

When an antigen enters the body for the first time, and the body responds to it.

30
Q

Why is the primary response slow?

A

Because there aren’t many B-cells that can make the antibody needed to bind to the antigen.

31
Q

What happens after being exposed to the antigen in a primary immune response?

A

T-cells and B-cells produce memory cells. These memory cells remain in the body for a long time.

32
Q

What is the difference between memory T-cells and memory B-cells?

A

Memory T-cells remember the specific antigen and will recognise it a second time around.
Memory B-cells record the specific antibodies needed to bind the antigen.

33
Q

What is a secondary immune response?

A

When the same pathogen enters the body again. This will produce a quicker, stronger immune response.

34
Q

What happens in clonal selection?

A

Memory B-cells are activated and divide into plasma cells that produce the right antibody to the antigen. Memory T-cells are activated and divide into the correct type of T-cells to kill the cell carrying the antigen.

35
Q

Why do you not show as many/no symptoms in secondary response?

A

Because the immune response often gets rid of the pathogen before you begin to show any signs of symptoms

36
Q

What do vaccines do?

A

Vaccines often contain antigens that cause your body to produce memory cells against a particular pathogen, without the pathogen causing disease.

37
Q

What is herd immunity?

A

When enough of the population is vaccinated and immune, that even people who are not vaccinated are then protected.

38
Q

What form are antigens in vaccines?

A

They may be free or attached to a dead or attenuated (weakened) pathogen.

39
Q

What is antigenic variation?

A

When pathogens change their surface antigens. Different antigens are formed due to changes in the genes of a pathogen.

40
Q

How does antigenic variation effect vaccine production?

A

Antigenic variation can make it difficult to develop vaccines against some pathogens.

41
Q

Name 2 examples of pathogens that can be hard to make vaccines for due to antigenic variation

A
  • HIV
  • influenza virus
42
Q

How do we cope with the antigenic variation of influenza?

A

Government and health authorities implement a programme of vaccination using the most suitable vaccine.

43
Q

Describe active immunity

A

Your immune system makes its own antibodies

natural- when you become immune after catching a disease
artificial- when you become immune after vaccination

44
Q

Describe passive immunity

A

The type of immunity you get from being given antibodies made by a different organism

natural- this is when a baby becomes immune due to the antibodies it receives from its mother, through the placenta and in breast milk

artificial- when you become immune after being injected with antibodies from someone else

45
Q

Compare active and passive immunity (4)

A
  1. A- requires exposure to antigen P- doesn’t require exposure to antigen
  2. A- It takes a while for protection to develop P- protection is immediate
  3. A- memory cells are produced P- memory cells aren’t produced
  4. A- protection is long-term because the antibody is produced in response to complementary antigen being present in body P- protection is short term because the antibodies given are broken down
46
Q

Explain how you can use monoclonal antibodies to target drugs to cancer cells

A

Cancer cells have antigens called tumor markers that are not found on normal body cells
Monoclonal antibodies can be made that will bind to tumor markers.
When the antibodies come into contact with the cancer cells they wil bind to the tumor markers

47
Q

What are monoclonal antibodies?

A

Monoclonal antibodies are antibodies produced from a single group of genetically identical B-cells (plasma cells). This means that they’re all identical in structure.

48
Q

Why are the side effects of antibody-based drugs lower than other drugs?

A

Because they only accumulate near specific cells

49
Q

Describe how monoclonal antibodies are collected

A
  1. Specific antigen injected into animal e.g. mouse
  2. B-lymphocytes producing complementary antibodies extracted
  3. B-lymphocytes fuse with myeloma cells to form hybridoma cells- these cells can divide and produce antibody
  4. Hybridoma cells cultured
  5. Monoclonal antibodies collected and purified
50
Q

What does a pregnancy test consist of?

A

A stick containing monoclonal antibodies specific to hCG:
- monoclonal antibodies attached to a blue bead
- monoclonal antibodies fixed to the test stick

51
Q

Describe what happens to the pregnancy test stick if the woman is pregnant

A

hCG in urine binds to monoclonal antibodies attached to a blue bead
monoclonal antibodies with hCG diffuses up dipstick
monoclonal antibodies fixed to stick bind to hCG
blue line forms

52
Q

Describe what happens to the pregnancy test stick if the woman is not pregnant

A

If no hCG is present, the beads will pass through the test area without binding to anything, and so wont go blue

53
Q

What is the ELISA test?

A

The enzyme-linked immunosorbent assay allows you to see if a patient has any antibodies to a certain antigen or any antigen to a certain antibody

54
Q

What can the ELISA test be used to test for?

A

pathogenic infections
allergies
anything you can make an antibody for

55
Q

How does the ELISA test work?

A

An antibody is used which has an enzyme attached to it. This enzyme can react with a substrate to produce a colored product. This causes the solution in the reaction vessel to change color.

56
Q

What does a color change demonstrate in an ELISA test?

A

If there is a color change it demonstrates that the antigen or antibody of interest is present in the sample being tested. In some ELISAs the quantity of antigen/antibody present can be worked out from the intensity of color change

57
Q

What is the difference between a direct ELISA and an indirect ELISA?

A

Direct ELISA uses a single antibody that is complementary to the antigen you’re testing for. Indirect ELISA is different because it uses two different antibodies.

58
Q

Explain the principle of a direct ELISA test

A
  1. monoclonal antibodies bind to bottom of test plate
  2. antigen molecules in sample bind to antibody. rinse excess.
  3. mobile antibody with ‘reporter enzyme’ attached binds to antigens that are ‘fixed’ on the monoclonal antibodies
  4. add substrate for reporter enzyme
    positive result = color change
59
Q

Explain the principle of a indirect ELISA test

A

An indirect ELISA test can be used to see if a patient posseses antibodies to the HIV virus. (HIV example)

  1. HIV antigen is bound to the bottom of a well in a well plate.
  2. A sample of the patients blood plasma which may contain several different antibodies is added to the well
  3. If there any HIV-specific antibodies they will bind to the HIV antigen. The well is then washed out to remove any unbound antibodies
  4. A secondary antibody that has a specific enzyme attached to it, is added to the well. This will bind to the HIV antibody if it is present. The well is then washed out to remove any unbound secondary antibody.
  5. A solution is added to the well, the solution contains a substrate which is able to react with the enzyme attached to the secondary antibody and produces a coloured product.

If the solution changes colour, it shows the patient has HIV antibodies in their blood, and is infected.

60
Q

What is HIV?

A

Human Immunodeficiency Virus affects the immune system. It eventually leads to AIDS when the helper T cell numbers in the body reach a critically low level.

61
Q

What is AIDS?

A

A condition where the immune system deteriorates and eventually fails. This makes someone with AIDS more vulnerable to other infections, like pneumonia.

62
Q

What does HIV do?

A

HIV infects (and eventually kills) helper T-cells, which act like host cells for the virus. Without helper T-cells, the immune system is unable to mount an effective response to infections because other immune system cells don’t behave the way they should.

63
Q

Describe the structure of HIV (4)

A
  1. core that contains RNA and some proteins (including enzyme reverse transcriptase which is needed for virus replication)
  2. an outer coating of protein called a capsid
  3. an extra outer layer called an envelope, made from membrane stolen from previous host cell
  4. attachment proteins stick out from the envelope to help HIV attach to the host helper T cell
64
Q

What cell does HIV attack?

A

helper T-cells

65
Q

Describe how HIV replicates (6)

A

HIV replicates inside its host T helper cells.

  1. The attachment protein attaches to a receptor molecule on the cell membrane of the host T helper cell.
  2. The capsid is released into the cell, where it uncoats and releases the genetic material (RNA) into the cell’s cytoplasm.
  3. Inside the cell, reverse transcriptase is used to make a complementary strand of DNA from the viral RNA template
  4. From this, double stranded DNA is made and inserted into the human DNA
  5. Host cell enzymes are used to make viral proteins from the viral DNA found within the human DNA
  6. The viral proteins are assembled into new viruses, which bud from the cell and go on to infect other cells.
66
Q

When are people with HIV classed as having AIDS?

A

When their symptoms of a failing immune system start to appear or their helper T-cell count drops below a certain level

67
Q

What are factors that effect the length of time it takes to progress from HIV to AIDS?

A
  • existing infections
  • strain of HIV
  • age
  • access to healthcare
68
Q

How can HIV be treated?

A

antiviral drugs called reverse-transcriptase inhibitors, these target the few virus- specific enzymes that exist e.g. reverse transcriptase

69
Q

How do you prevent the spread of HIV?

A
  • protected sex
  • not sharing needles
  • not sharing blood

Biology Year 1 (9 decks)

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