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Biology > Chapter 5- Cell Recognition And Immune System > Flashcards

Chapter 5- Cell Recognition And Immune System Flashcards

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1
Q

What is a pathogen? Name an example.

A

A microorganism that causes infectious diseases.

E.g. Virus, bacteria, protists, fungi

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2
Q

What is a toxin?

A

A poisonous substance produced by a living organism.

Animals can produce toxins to kill prey.

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3
Q

What is an antigen?
- refer to genetic mutations.

A

A foreign molecule (protein) that stimulates an immune response.

  • Genetic mutations in a pathogen can cause antigens to change… therefore a person has to launch an new immune response.
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4
Q

The Immune response 1

Describe the process of phagocytosis.

A
  1. Phagocyte is attracted to pathogen by chemicals.
  2. Phagocyte has many receptors on membrane, these attach to chemicals on pathogen
  3. Lysosomes migrate towards phagosome (formed via engulfing pathogen)
  4. Lysosomes release lysozymes which hydrolyse the pathogen
  5. Products are then absorbed by phagocyte.
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5
Q

The Immune response 2

Describe the cellular response

A
  1. After phagocytosis, the phagocyte contains debris from the hydrolysed pathogen
  2. It contains a useful antigen, which is moved towards the cell membrane of the phagocyte
  3. Only 1 Helper T cell receptor fits antigen via process of clonal selection
  4. Mitosis allows cloning of helper T cell so many activated cytotoxic helper T cells are produced
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6
Q

What do helper T cells do after cellular response?

A
  • become memory cells: these circulate in blood ready to respond to future infection by same pathogen
  • Stimulate B cells to divide
  • stimulates phagocytosis
  • Activates cytotoxic cells which kill infected cells by making holes in membranes of them
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7
Q

The Immune Response 3

Describe the humoral response

A

It uses B cells that are stimulated to divide from cellular response

  1. B cell has specific receptor for that antigen. It engulfs the pathogen using this
  2. A vesicle forms round the pathogen and lysozymes hydrolyse it
  3. Processed antigen is then portrayed on outside of B cell
  4. Helper T cell binds to B Cell and stimulates clonal selection of B cells by mitosis
  5. These B Cells produce plasma cells and memory cells
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8
Q

What do plasma and memory cells do?

A

Primary response - Plasma Cells attach to antigens on pathogens to destroy it via secreting antibodies

Secondary response - Memory cells circulate in blood ready to respond to future infection by same pathogen
- they do this by dividing into plasma cells.

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9
Q

What is an antibody? Label structures

A

A protein able to bind to a specific antigen. They are secreted by plasma cells.

  1. Variable region - specific amino acid sequence
  2. Antigen binding site
  3. Light and heavy polypeptide chain
  4. Hinge region - disulfide bridge
  5. Chain of sugar molecules
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10
Q

How do antibodies destroy antigens?

A
  1. Agglutination - antibodies each bind to an antigen on 2 separate pathogens, causing them to clump via a network of antigen-antibody complexes
  2. Subsequent phagocytosis - the clump makes it easier for phagocytes to locate pathogens - antibodies serve as marker.
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11
Q

Differences between active and passive immunity [3]

A
  1. In ACTIVE antibodies are secreted by plasma cells whereas in PASSIVE antibodies are introduced into body from outside
  2. ACTIVE is longer term as memory cells are developed whereas PASSIVE is shorter term because no memory cells are created.
  3. ACTIVE takes longer to develop whereas PASSIVE is fast acting
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12
Q

Examples of active and passive immunity

A

ACTIVE:
Natural - normal immune response
Artificial - vaccination

PASSIVE:
Natural - antibodies from placenta to foetus
Artificial - anti-venom

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13
Q

How does vaccination work? - non exam style

A
  • vaccines contain isolated antigen molecules, dead pathogens or live but attenuated (weakened) pathogens. However must still have required antigen on surface
  • when injected: leads to primary response and memory cells are made
  • on second exposure- memory cells bind to antigen and:
    1. Rapidly divide into plasma cells which leads to a faster production of antibodies at a higher concentration.
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14
Q

What is herd immunity?

A
  • form of indirect protection from infectious disease.
  • occurs when a sufficient % of population are immune to infection (through vaccination) which results in a reduced chance of infection for those who lack immunity.
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15
Q

Why is herd immunity important?

A

IMPOSSIBLE TO VACCINATE EVERYONE:
- infants immune system is still developing
- some people are very ill and can’t be vaccinated
- allergies
- ethical/religious obligations

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16
Q

What makes a successful vaccination programme? [5]

A
  • economically viable to produce on large enough scale
  • easy to administer
  • few side effects
  • easy to achieve herd immunity
  • means to produce, store and transport vaccine
17
Q

Why can vaccines fail to eliminate disease?

A
  • defective immune systems
  • catch disease too soon after
  • antigen variability
  • many types of pathogen for same disease
  • some pathogens hide from immune system
  • ethical/religious obligations
18
Q

List some potential problems with vaccines

A
  • inactive microorganisms may become active
  • attenuated microorganisms may mutate and become harmful
  • non pathogenic microorganisms may mutate and become harmful
  • genetic info/ protein in it may harm cells
  • vaccine not effective against all strains of pathogen
  • false positives
19
Q

What is a monoclonal antibody?

A

Antibodies with the same tertiary structure produced from a genetically identical set of plasma cells.
- all bind to same antigen

20
Q

List the 2 main medical uses of monoclonal antibodies?

A
  1. Targeting medication to specific cell types by attaching therapeutic drug to antibody.
    - deliver cytotoxic drugs to cancer cells which kill them
  2. Medical diagnosis: e.g. a pregnancy test identifies presence of a pregnancy hormone (hCG) in urine sample.
21
Q

Ethical issues with monoclonal antibodies use.

A
  • they are made using mice that have to be given cancer
  • potential to cause side effects that may be serious even if shown to be safe in LAB animals.
22
Q

EXAM STYLE QUESTION
How are pathogens destroyed by phagocytosis? 4 marks

A
  1. Phagocyte attracted by substance;
  2. Pathogen engulfed;
  3. Enclosed vesicle/ phagosome;
  4. Phagosome fuses with lysosome;
  5. Lysosome contains lysozymes;
  6. Pathogen digested/ hydrolysed;
23
Q

EXAM STYLE QUESTION
Explain why antibodies bind to a specific antigen. 3 marks

A
  1. Antibody variable region has specific amino acid sequence;
  2. Shape/ tertiary structure of binding site is complementary to antigens;
  3. Forms antigen- antibody complex;
24
Q

EXAM STYLE QUESTION
Describe how phagocytosis of a virus leads to the presentation of it’s antigens. 3 marks

A
  1. Phagosome fuses with lysosome;
  2. Virus destroyed by lysozymes;
  3. Antigens are displayed on the cell membrane;
25
Q

EXAM STYLE QUESTION
Describe how the presentation of antigens leads to secretion of antibodies. 3 marks

A
  1. Helper T cell binds to antigen on phagocyte;
  2. This helper T cell stimulates a specific B cell to divide;
  3. B cell divides by mitosis;
  4. It forms plasma cells that release antibodies;
26
Q

EXAM STYLE QUESTION
Why do vaccines need to be refrigerated?

A
  • antigens are proteins
  • high temperature will break ionic/ hydrogen bonds in protein
  • antigen will denature
  • results in no immune response.
27
Q

EXAM STYLE QUESTION
Describe how B lymphocytes would respond to vaccination against a virus. 3 marks

A
  1. B cell binds to viral antigen;
  2. B cells divides by mitosis;
  3. Plasma cells release antibodies;
  4. B cells produce / develop into memory cells;
28
Q

EXAM STYLE QUESTION
Explain how vaccination would lead to a person developing immunity to a pathogen. 5 marks

A
  1. Vaccine contains antigen/ attenuated / dead pathogens;
  2. T cells activate B cells;
  3. B cells divide by mitosis;
  4. Plasma cells produce antibodies;
  5. Memory cells produced meaning more antibodies in secondary response;
29
Q

How do viruses (HIV) replicate?

A
  • Attachment proteins attach to receptors on helper T cell
  • RNA enters the cell
  • Reverse transcriptase converts RNA to DNA
  • Viral protein produced
  • virus assembles and released from cell
30
Q

EXAM STYLE QUESTION

Describe how HIV is replicated once inside helper T cells [4marks]

A
  1. RNA is converted into DNA using reverse transcriptase
  2. DNA inserted into helper T cell DNA
  3. DNA is transcribed into HIV RNA
  4. This is then translated into viral proteins
31
Q

Describe the role of antibodies in producing a positive result in the ELISA test [4]

A
  1. First antibody binds to antigen
  2. Second antibody with enzyme attached is added
  3. Second antibody attaches to the antigen
  4. This causes a colour change

Biology (22 decks)

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