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Biology Paper 1 > 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

Give four examples of non-self antigens

A
  1. Pathogens
  2. Toxins
  3. Abnormal body cells (cancer cells)
  4. Transplant tissue
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2
Q

Define antigen

A
  • any part of an organism or substance
  • that is recognised as non-self by the immune system
  • stimulating an immune response
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3
Q

Describe the effect of antigen variability on disease and disease prevention

A
  1. Genetic variation can cause the** tertiary structure of the antigen to change**
  2. Memory cells will not recognise the antigen - NO SECONDARY IMMUNE RESPONSE
  3. A new primary response is needed - this takes time so the** individual gets infected**
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4
Q
A
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5
Q

Give two examples of non-specific immune response

A
  1. physical barrier
  2. phagocytosis
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6
Q

Give two examples of specific immune response

A
  1. cell mediated response (T-lymphyocytes)
  2. humoral response (B-lymphocytes)
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7
Q

Give the four physical barriers the body uses to defend against pathogens

A

1.** skin** - layer of dead cells so acts as a physical barrier, fatty acids in the sebum inhibit growth of microorganisms
2.** cilia in the nose and gas exchange system** - transport mucus (contains trapped dirt and microorganisms) and move it up the respiratory tract so it can be swallowed and killed by stomach acid
3.** hydrochloric acid **in the stomach
4. lysozymes in tears - digest bacterial cell walls

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8
Q

Where are phagoctyes produced?

A

bone marrow

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9
Q

Where are phagocytes found?

A

blood and tissues

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10
Q

What are the two types of phagocytes?

A
  1. neutrophils - short lived, engulf pathogens in endocytosis
  2. macrophage - long lived, initiate an immune response by cutting up and displaying the antigens on their surface for lymphocyte recognition
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11
Q

Describe the process of phagocytosis?

How do lysozymes break down the pathogens?

A
  1. cytokines or debris on the pathogen/abnormal cell attracts the phagoctye
  2. phagocyte attaches to the pathogen, engulfing it
  3. phagosome vesicle forms around the pathogen
  4. lysososomes fuse with the phagosome
    5.** lysozymes are releases - these hydrolyse** the molecules in the pathogen
  5. soluble products are absorbed into the phagocytic cytoplasm
  6. foreign antigens are presented on the phagocyte surface
  7. ANTIGEN PRESENTING CELL

They hydrolyse the cell walls

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12
Q

What is the role of histamines in phagocytosis?

A
  • damaged tissue releases histamines
  • causes blood vessels to dilate (skin becomes hotter)
  • speeding up arrival of phagocytes to the site
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13
Q

Where are T-lymphyocytes made and matured?

A

divide by mitosis in the bone marrow but mature in the THYMUS

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14
Q

Describe the role of T-lymphyoctes

A
  • CELL MEDIATED RESPONSE (Primary response)
  • direct the immune response
  • ONLY in response to ANTIGEN PRESENTING CELLS (phagocytes, cancer cells, transplant cells, body cells infected by a virus)

T-cellw WILL NOT respond to antigens detached from cells and within bodily fluids such as blood

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15
Q

Give the four main antigen-presenting cells which T-lymphyocytes respond to

A
  • infected body cells (viral antigens on the surface)
  • phagocyte/macrophage
  • transplant cells (antigens are a different shape to self antigens)
  • cancer cells (self antigens have become abnormal)
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16
Q

Why do T-lymphyocyes not respond to self-cells?

A
  • the body has MANY T-lymphocytes
  • any lymphyocyes that have receptors complementary to body cells will die via programmed cell death BEFORE maturation
  • only remaining lymphocytes respond to FOREIN ANTIGENS
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17
Q

Describe the process of cell-mediated response

A
  1. Antigen presenting cell moves in the blood
  2. Complementary receptors on helper T-cells bind to the presented antigens
    4.** T-cells are activated to divide by mitosis** to form clones
  3. They can differentiate into: more helper T-cells, cytotoxic T-cells, memory cells and suppressors
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18
Q

Describe the function of helper T-cells

A

secrete cytokines which…
- activate cytotoxic T-cells
- stimulate phagocytosis
- stimulate B-cells to divide into antibody secreting plasma cells AND memory cells

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19
Q

Describe the function of cytotoxic T-cells

A
  • secrete a protein called PERFORIN
  • embeds in the cell surface membrane and **makes a pore **in the cell surface membrane
  • cell membrane is now freely permeable which causes cell death

common in viral infections - body cells are sacrificed to prevent viral replication

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20
Q

Describe the function of memory cells

A

recognise foreign antigens which initiates the secondary response

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21
Q

Describe the role of B-lymphyocytes

A
  • HUMORAL RESPONSE
  • antibody production for destruction of pathogens
  • respond to antigens
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22
Q

where are B-cells produced and matured?

A

produced and matured in the BONE MARROW

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23
Q

Where are B-cells found?

A

body fluids such as blood, lymph fluid and tissue fluid

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24
Q

Describe the process of humoral response

A
  1. Specific B-lymphyocytes engulf pathogenic antigens (from the blood) via endocytosis
  2. foreign antigens are presented on the B-cell surface
    3.** activated T-helper** cells **bind to the processed antigens **on the B-cell (clonal selection)
  3. B-cells are activated to divide by mitosis (clonal expansion)
  4. clones differentiate to form plasma cells and memory cells
  5. plasma cells produce antibodies which bind to antigens on invading pathogens to form an antigen-antibody complex
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25
Q

Describe the function of plasma cells

A
  • secrete SPECIFIC antibodies
  • antibodies attach to pathogen antigen and destroy it
  • immediate defense
26
Q

Describe the function of memory cells

A
  • circulate in blood and tissue fluid (can live for decades)
  • recognise the antigens on a pathogen
  • divide rapidly and develop into plasma cells which produce antibodies
  • This is the SECONDARY IMMUNE RESPONSE
27
Q

Describe the primary immune response

A

Plasma cells produce antibodies (after clonal selection and expansion in cell mediated response- concentration of antibody is low in the primary response
-immediate
-short lived
-slow to make impact

28
Q

Describe the secondary immune response

A

Memory T and B cells recognise the antigen and so divide rapidly to produce plasma cells for antibody production
-response is more rapid and of greater intensity
-long term defense due to memory cells

29
Q

Define clonal selection

A

process of matching the antigens to antigen receptors on B and T lymphyocytes

30
Q

Define antibody

A

proteins produced by plasma cells which bind to antigens as part of the immune response

31
Q

Describe the structure of an antibody

A
  • four polypeptide chains = 2 light and 2 heavy
  • two variable regions (unique tertiary structure) which change in each antibody
  • two antigen binding sites which are complementary to the foreign antigen = form an ANTIGEN-ANTIBODY complex
32
Q

Describe how antibodies destroy pathogens

A
  1. plasma cells secrete SPECIFIC antibodies
  2. antibodies bind to their complementary antigens
  3. there are TWO binding sites so antibodies can simultaneously bind to two cells
  4. causes pathogens to clump
  5. AGGLUTINATION
  6. this neutralise the pathogens or acts as a marker for phagocytes
33
Q

Define monoclonal antibody

A

antibodies produced from one type of plasma cell which are complementary to one type of antigen

34
Q

How are monoclonal antibodies used in targeting drugs (such as in cancer treatment)?

A
  1. specific antibodies are produced which will bind to the tumour markers
  2. antibodies block uncontrolled growth or have radioactive/cytotoxic drugs attached which kill cancer cells
  3. As the method is targeted there are fewer side effects
35
Q

How can monoclonal antibodies be used in medical diagnosis (eg pregnancy tests)?

A

Pregnancy test example:
1. HCG in the urine of a pregnant woman will bind to the antibody (which has been attached to blue beads)
2. urine moves down the strip, carrying the beads with it
3. second strip will turn blue as the immobilised antibody binds to the HCG on the blue beads

36
Q

What are the two main ethical issues with monoclonal antibodies?

A
  1. use of animals in production
  2. organ failure - over production of T-cells can lead to an excessive immune response in some people
37
Q

How have scientists overcome the issue of animal sourced monoclonal antibodies causing an immune response in humans?

A
  1. Genetically modifying the antibody polypeptide chains so that the amino acid sequences are now human not mouse or rabbit sequences
  2. Altering the type and position of the sugar groups (antibodies are glycoproteins) attached to the heavy polypeptide chains to reflect those found on human antibodies
38
Q

Describe how the ELISA test is used to detect antibodies/antigens

A
  1. antigens are bound to a well
  2. a plasma sample is added, the** specific antibodies will bind to their complementary antigen**
  3. wash to remove any unbound antibody
  4. add a secondary antibody which is complementary in shape to the first antibody (enzyme is attached) - this** binds** to the primary antibody
  5. wash to remove any unbound antibody (and prevent a false politive)
  6. colourless substrate for the enzyme is added
  7. formation of enzyme-substrate complexes catalyses a** colour change**
39
Q

Define vaccine

A

suspension of antigen or attentuated pathogens which induce artificial immunity in the body

40
Q

How do vaccines stimulate the formation of memory cells?

A
  1. vaccines contain antigens
  2. antigen is engulfed by a B-cell which becomes antigen presenting
  3. activated T-helper cell binds to complementary protein receptor on the B-cell which stimulates division by mitosis into clones
  4. plasma cells produce antibodies for the primary immune response
  5. memory cells recognise familiar antigens to stimulate the secondary immune response
41
Q

Why are vaccines often given several times over a few months?

A
  1. stimulates a repeated immune response
  2. increasing the memory cell concentration
  3. so there are enough memory cells to give immunity
42
Q

Why do some vaccines not eradicate disease?

A
  1. vaccine may not stimulate an immune response in some individuals
  2. there are many pathogen variations so it is difficult to develop effective vaccines
  3. people could develop the disease before their immune system can fight it - passing it onto others
43
Q

What is antigenic variation?

A
  1. pathogens mutate frequently
  2. antigens may not be recognised by memory cells
44
Q

What are the main factors which create a successful vaccination programme?

A
  1. few side effects
  2. ability to produce, store and transport the vaccine
  3. ability to reach most of the population - to stimulate HERD IMMUNITY
  4. minimal ethical issues (risk of harm, animal testing)
45
Q

Define herd immunity

A

when a sufficiently large proportion of the population has been vaccinated, making it difficult for the pathogen to spread throught the population
(less chance that a suseptable individual will come into contact with an infected person)

46
Q

What are the four conditions of passive immunity?

A
  1. antibodies introduced from an outside source
  2. No memory cells
  3. short term protection - antibodies eventually break down
  4. provides immediate protection
47
Q

Give examples of natural and artificial passive immunity

A

natural - baby getting its mothers antibodies
artificial - injected with antibodies

48
Q

What are the four conditions for active immunity?

A
  1. antibodies produced by the bodies own immune system
  2. memory cells
  3. long term immunity
  4. takes a while to develop initially
49
Q

Give examples of natural and artificial active immunity

A

natural - catching the disease and carrying out an immune response
artificial - vaccination

50
Q

What is the attachment protein?

A

used by viruses to identify and attach to host cells

51
Q

What is the lipid envelope?

A

stolen from the membrane of the host helper T-cell (not present in all viruses)

52
Q

What is the capsid?

A

protein layer that encloses two single strands of RNA and some enzymes

53
Q

What is RNA?

A

contains the genetic material needed for the virus to reproduce

54
Q

What is reverse transcriptase?

A

catalyses the production of viral DNA from RNA

55
Q

Describe the process of HIV replication?

A
  1. attachment protein on the HIV binds to the complementary receptor on the host helper T-cell
  2. capsid fuses with the cell membrane - RNA and reverse transcriptase are released into the cytoplasm
  3. reverse transcriptase catalyses the synthesis of DNA from viral RNA
  4. viral DNA is inerted into human DNA (remains inactive for many years)
  5. viral DNA becomes active and creates** mRNA from enzymes**
  6. mRNA** diffuses out** the nuclear pore
  7. mRNA has the instructions for the cell to synthesise new viruses
  8. HIV particles** break away **from T-helper cells (they take part of the cell membrane to form their lipid envelope)
56
Q

Define AIDS

A

acquired immune deficiency syndrome

57
Q

Describe how HIV can lead to AIDS if left untreated?

A
  1. helper T-cells are constantly dividing by mitosis, resulting in more genetically identical (inactive) HIV DNA
    (each time the cell divides it copies the viral DNA)
  2. viral DNA becomes active and lots of HIV particles are synthesised
  3. helper T-cells die so there are fewer helper T-cells in the blood
  4. T-helper cells stimualte B-cell division, phagocytosis and activate cytotoxic T-cells
  5. less plasma cells = fewer antibodies
  6. compromised immune system means individual is more likely to die from an opportunistic pathogen
58
Q

How is HIV currently treated?

A

no cure or vaccine
BUT antiretroviral drugs can slow progression by targetting virus specific enzymes

59
Q

Why can antibiotics not be used against HIV?

A

-antibiotics work by weakening the cell wall, causing cells to burst (osmotic lysis)
- but HIV is a particle NOT a cell

Antibiotics also can’t reach viruses when they are in a cell

60
Q

How does the HIV virus avoid being destroyed by lymphocytes?

A

constantly changes its protein coat

Biology Paper 1 (15 decks)

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