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Biology > 3.2.4 Cell Recognition And Immunity > Flashcards

3.2.4 Cell Recognition And Immunity Flashcards

1
Q

What are pathogens?

A

Disease-causing microorganisms

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2
Q

What are the two defence mechanisms the body has to kill pathogens?

A

Physical and chemical
-first line defences prevent the entry of pathogens eg. Skin, eyes, saliva etc
-the immune system fights pathogens which have entered the body.

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3
Q

Summarise how the immune system defends against pathogens

A

Recognition of foreign cells and targeting pathogenic cells, and inflammation of the region that has been invaded by a pathogen to trigger further immune responses.

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4
Q

What is the specific immune response?

A

An immune response which is specific to the particular pathogen that has invaded the body.

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5
Q

What is the non-specific immune response?

A

An immune response which is not specific to the particular pathogen that has invaded the body, but is the same regardless of the pathogen present.

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6
Q

Why are antigens needed?

A

As white blood cells must be able to distinguish the body’s own cells from foreign ones, in order to identify the presence of pathogens or foreign substances.

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7
Q

What is an antigen?

A

A toxin or other foreign substance, usually on the surface of foreign cells, which induces an immune response.

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8
Q

Why are antigens so unique?

A

They are usually proteins, so their highly specific 3D tertiary structure means many different shapes can be made.

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9
Q

What do antigens allow us to identify?

A

Pathogens eg. Bacteria, viruses, protists and fungi
Non-self materials
Toxins
Abnormal body cells (mutations)

Note: antigens are also on self-cells but do not trigger an immune response as they are not foreign.

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10
Q

What are lymphocytes?

A

Lymphocytes are the cells which recognise different shaped antigens

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11
Q

Why do lymphocytes not recognise self-cells as foreign?

A

Lymphocytes are made when you are a foetus, so you are unlikely to be exposed to any cells other than self-cells.
The lymphocytes complementary to the antigens on self-cells will die or production will be suppressed.
The only remaining lymphocytes are complementary to pathogenic and non-self cells.
This means that the immune system does not attack the body’s own cells, but only foreign ones.
If this process does not occur correctly, it causes autoimmune diseases.

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12
Q

What is antigen variability?

A

As pathogen’s DNA can mutate frequently, the shape of the antigen can change.
This means that any previous immunity is no longer effective, as all of the memory cells in the blood will have a memory of the old antigen shape.
This is known as antigen variability.
It means that there is no immune response, so the person will suffer from the disease again.

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13
Q

What are phagocytes?

A

White blood cells that recognise and engulf pathogens through the process of phagocytosis, which is an example of a non-specific immune response.

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14
Q

What is a macrophage?

A

A phagocyte involved in non-specific immunity, but also plays a role in the specific immune response.

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15
Q

What is a neutrophil?

A

A phagocyte involved in the non-specific immune response only.

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16
Q

Describe the process of phagocytosis?

A
  1. The phagocytes are in the blood, and a phagocyte is attracted to the location of the pathogen by chemoattractants, chemicals released by the pathogen.
  2. The phagocyte moves towards the pathogen, where it identifies the pathogen due to the specific shape of its antigens. The phagocyte’s receptor binding points bound to the antigen on the pathogen.
  3. The cell surface membrane engulfs the pathogen by forming a phagosome, by endocytosis. Lysosomes begin to move towards the phagosome.
  4. Lysosomes release lysozymes which are lytic enzymes, into the phagosome. The lysozymes break down the pathogen in the phagosome by hydrolysis.
  5. The soluble products from the breakdown of the pathogen are absorbed by the phagocyte. They display the antigen of the pathogen on their surface to trigger a further immune response.
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17
Q

What is the name of the chemicals released by the pathogen that attract the phagocyte?

A

Chemoattractants

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18
Q

What organelle forms the phagosome?

A

Cell-surface membrane

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19
Q

What is the name of the lytic enzymes released into the phagosome by lysosomes?

A

Lysozymes

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20
Q

What are t-lymphocytes?

A

T-lymphocytes are a specific type of lymphocyte that are involved in the cell-mediated immune response, meaning they respond to foreign material inside body cells.

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21
Q

Where are all lymphocytes made?

A

In the bone marrow

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22
Q

Where to t-lymphocytes mature?

A

In the thymus

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23
Q

What cells to t-lymphocytes respond to?

A

T-lymphocytes respond to cells that present a non-self antigen on their surface. (APCs- antigen presenting cells)
-infected body cells
-a phagocyte that has engulfed a pathogen
-cells from a transplanted tissue
-cancer cells

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24
Q

Describe the process of the T-lymphocyte immune response?

A

A phagocyte engulfs a pathogen and has presented its antigens on the surface (so is an antigen presenting cell).
This activates the specific and complementary T-lymphocytes, and their T-cell receptor binds to the antigens.
The activated T-cells divide by mitosis to make large numbers of clones, which produces two types of T-cells.
Helper-t-cells secrete cytokines (chemicals) which stimulate phagocytes to engulf pathogens, and the b-cells to release antibodies.
Killer-t-cells attach to the foreign antigens on the surface of infected cells that present the complementary antigen. They also secrete cytotoxins, which are chemicals that kill infected cells.

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25
Q

What are B-lymphocytes?

A

Ha type of lymphocyte that is involved in humoral immunity, defending the body against pathogens in bodily fluids by producing antibodies which respond to foreign material outside of cells.

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26
Q

Where are b-lymphocytes stored?

A

Lymph nodes

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27
Q

Where do b-lymphocytes mature?

A

Bone marrow

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28
Q

What pathogens do b-lymphocytes respond to?

A

All pathogens - bacteria and viruses

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29
Q

Describe how B-lymphocytes play a role in humoral immunity?

A

When maturing in the bone marrow, each b-cell produces a different antigen receptor/antibody.
They all circulate and concentrate in lymph nodes.
When an antigen enters the body, the b-cell with the complementary antibody is stimulated to divide by mitosis. This is activated by T-helper cells.
Some B-cells become plasma cells, and some become memory cells.
Plasma cells secrete many antibodies into the circulatory system. These antibodies are complementary to the shape of the antigen on the pathogen, which causes the pathogens to clump together when they bind to them. This renders them harmless and prepares them for destruction (opsonisation).
Memory cells remain in the body in case of a secondary infection.

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30
Q

How do b-lymphocytes divide?

A

By mitosis

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31
Q

What are the two cells produced by the division of b-lymphocytes?

A

Plasma cells and memory cells

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32
Q

What is the role of plasma cells?

A

They secrete many antibodies into the circulatory system. These antibodies are complementary to the antigen shape on the pathogen, which causes pathogens to clump together when they bind to them. This renders them harmless and prepares them for destruction (opsonisation).

33
Q

What is the role of memory cells?

A

They remain in the body in case of a secondary infection, to enable a more rapid immune response.

34
Q

What are antibodies?

A

Antibodies are globular proteins that bind to antigens as part of the body’s immune response to foreign pathogens.

35
Q

Describe the structure of antibodies

A

They have a quaternary structure that consists of 2 long polypeptide chains and 2 short polypeptide chains.

36
Q

What is the constant region?

A

The part of the antibody that has the same amino acid sequence for all antibodies.

37
Q

What is the variable region?

A

The variable region has a different amino acid sequence for each antibody, which changes the ionic, hydrogen and disulphide bonds in the tertiary structure. This means that a range of differently shaped antibodies can be produced to target many different antigens.

38
Q

What are the receptor binding sites?

A

They allow the antibodies to attach to the surface of plasma cells before being released.

39
Q

What is the hinge region?

A

It gives the antibody flexibility so that it can bind to the antigen at any angle.

40
Q

What is the antigen binding site?

A

They allow the antibody to bind to the complementary antigen.

41
Q

What is the role of antibodies?

A

To attach to antigens to immobilise them

42
Q

Describe how antibodies play a role in immunity

A

Antibodies are produced by plasma cells that have a complementary shape to the antigens on the pathogen.
When they collide with pathogens, they bind to antigens on its surface to form an antigen-antibody complex.
This causes the pathogens to become clumped together by a process called agglutination.
This attracts phagocytes to engulf them, or neutralises the toxins produced by the pathogen.

43
Q

What is agglutination?

A

When antigens become clumped together and immobilised when antibodies bind to them.

44
Q

What is a polyclonal response to a pathogen?

A

When multiple different antibodies need to be produced to kill the pathogen, as it has multiple different antigens on its surface.

45
Q

What are monoclonal antibodies?

A

Antibodies that are specific to one type of antigen that can be isolated and cloned through repeated mitosis.

46
Q

Give some uses of monoclonal antibodies

A

Pregnancy tests
Covid tests
Testing for cancer
Treating cancer
Passive immunity vaccines

47
Q

Briefly outline how monoclonal antibodies are produced

A

A mouse is injected with the antigen that the MABs are being produced for.
The mouse’s immune system produces plasma cells, which produce the complementary antibody to the injected antigen.
The plasma cells from the moulds are fused with a tumour cell to form a hybridoma cell that divides rapidly
The hybridoma cell is stimulated to divide by mitosis.
A large number of specific and complementary antigens are produced, which are complementary in shape to the antigen that the mouse was injected with.

48
Q

How can direct monoclonal antibody therapy be used to treat certain cancer?

A

The monoclonal antibodies are created with a binding site complementary in shape to the antigens on the outside of cancer cells.
These are given to the patient and attach to cancer cell antigens, to prevent chemicals binding to the cancer cell that are responsible for uncontrolled cell division.
This prevents the cancer cells from dividing further and therefore the tumour from growing.
As they are specific to the antigens on the cancer cells, they do not cause harm to normal body cells.

49
Q

How can indirect monoclonal antibody therapy be used to treat cancer?

A

Drugs are attached to monoclonal antibodies which are complementary in shape to antigens on the outside of cancer cells.
The drugs are delivered directly to the cancer cells and kill them.
This is often referred to as bullet drugs.

50
Q

What is the ethical issue of using monoclonal antibodies?

A

Requires mice to produce the antibodies which creates debate as to whether this use of animals is justified to enable better treatment and diagnosis of diseases in humans.

51
Q

What is the ELISA test used for?

A

To diagnose medical conditions eg. Prostate cancer

52
Q

Describe how to carry out the ELISA test to diagnose prostate cancer

A

Antibodies to the prostate specific antigen are bound to the well of the test plate.
Blood from the patient is added so that the PSA binds to the antibodies if present (other antigens do not bind as they are not complementary).
Antibody with attached enzyme is added, which binds to the PSA if present, or is washed out if not bound.
A colourless liquid is added.
If the enzyme is still present, the enzyme converts the colourless liquid to a coloured product if still present.

The colour change indicates that the patient has prostate cancer as the PSA was present so the enzyme remained in the test plate as the antibody bound to the PSA.

53
Q

How can a person become exposed to a pathogen?

A

By being infected by the pathogen
By being vaccinated

54
Q

How do antibodies work in immunity?

A

They bind to antigens so that they clump together, rendering them harmless. This process is known as agglutination.

55
Q

Describe and explain the primary immune response

A

In the initial exposure to the antigen, the antigen is recognised as foreign by phagocytes. Between 0-5 days after the initial exposure, the phagocytes engulf the pathogen and stimulate T-cells to divide by mitosis to form T-helper cells, which stimulate B-cells.
B-lymphocytes divide by mitosis to form plasma cells and memory cells. Through clonal selection, plasma cells produce antibodies so the concentration of antibody in the blood increases. However, the response is slow and the quantity of antibody is low, as time is taken between the initial exposure and the immune response to take place.
After the initial exposure, memory cells are produced by B and T cells, which remain in the lymphatic system in case of a secondary exposure.

56
Q

Describe and explain the secondary immune response

A

In the secondary exposure on day 20, memory cells recognise the antigen’s tertiary structure from the previous infection, so divide rapidly by mitosis and differentiate to form plasma cells, which produce antibodies.
This produces a rapid immune response with a high quantity of antibodies, so the pathogen is killed.

57
Q

What is a vaccine?

A

Vaccines are a weak or inactive form of the antigens of a specific pathogen which triggers an immune response.

58
Q

What are the 3 different forms of vaccines?

A

Live-attenuated vaccine
Dead/inactivated pathogens
Isolated antigens

59
Q

What is a live-attenuated vaccine?

A

Heat treated pathogens which have been weakened

60
Q

What are dead/inactive vaccines?

A

Dead or inactive pathogens as they are unable to reproduce.

61
Q

What are isolated antigen vaccines?

A

Cell surface proteins or antigens that have been isolated from the pathogen itself.

62
Q

How do vaccines lead to immunity?

A

Vaccines lead to immunity as they cause memory cells to be created, so on secondary infection, the immune response is rapid and effective.

63
Q

What is the difference between active and passive immunity?

A

Active immunity is when the antibodies are made within the body, but passive immunity is when the antibodies are introduced to the body from the external environment.

64
Q

What is herd immunity?

A

When enough of the population are vaccinated that the pathogen cannot spread easily amongst the population. This protects the population who cannot be vaccinated and eventually can eradicate diseases.

65
Q

What is antigenic variability?

A

When pathogen’s DNA mutates frequently, so codes for different proteins, so the tertiary structure of the antigens changes shape.

66
Q

What is the problem with antigenic variability?

A

The memory cells produced in the primary immune response will not recognise the antigens on the pathogen, so the primary immune response restarts so is slower and less effective.
This means vaccines need to be updated regularly to prevent people becoming ill again.

67
Q

What are viruses?

A

Viruses are pathogens that replicate by invading T-helper cells in order to reproduce, killing T-helper cells in the process.
They are not considered living as they are unable to reproduce alone.

68
Q

Are viruses smaller or larger than bacteria?

A

Viruses are much smaller than bacteria

69
Q

What is the role of reverse transcriptase?

A

An enzyme that converts RNA to DNA so that it can combine with the host cell’s DNA.

70
Q

What is an attachment protein?

A

A protein on the exterior of the envelope that enables the virus to attach to the host T helper-cells.
It is manufactured by the RER in the host cell.

71
Q

What are the structures in a viral particle?

A

Capsid (protein coat)
Matrix
RNA
Lipid envelope (made from host cell’s membrane)
Attachment proteins
Reverse transcriptase

72
Q

Explain why antibiotics cannot be used to treat viral infections

A

Antibiotics target structural differences between eukaryotic and prokaryotic cells, so would be ineffective when targeting viruses as they do not have the same structures.

73
Q

Why are there few drugs available to treat viruses?

A

Viruses reproduce inside host cells so are inaccessible without damage to healthy cells.

74
Q

What type of virus is HIV?

A

HIV is a retrovirus

75
Q

What is a retrovirus?

A

A group of viruses that have the ability to make DNA from RNA as they have reverse transcriptase.

76
Q

How does HIV infect host cells?

A

It binds to receptor proteins on T-helper cells and incorporates its genetic material into the cell.
This results in the production of new HIV particles which then leave the T-helper cell, surrounded by some of the cell membrane.

77
Q

How does HIV lead to AIDS?

A

Because it targets the immune system which severely weakens it.
-stops plasma/memory cells being made
-stops stimulation of cytotoxic T-killer cells
-stops stimulation of phagocytosis

78
Q

Describe how HIV replicates?

A

HIV enters the body by blood contamination, semen, wounds or by perinatal transmission across the placenta.
HIV attaches to the CD4 receptor protein on the surface of Helper T-cells.
The membranes fuse and HIV’s RNA and reverse transcriptase are released into the cytoplasm.
Reverse transcriptase copies the viral RNA strand into a DNA copy.
Viral DNA is integrated into the host cell’s DNA (but it can remain inactive for a long time).
mRNA is transcribed so the helper T-cell makes new viral proteins, and therefore new viral particles.
Viral particles are released which damages T-cell membrane.

Biology (17 decks)

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