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AQA A Level Biology > Immunology - Mr Frank > Flashcards

Immunology - Mr Frank Flashcards

3.2.4

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1
Q

What is the immune system?

A

A collection of cells distributed throughout our body

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2
Q

Why is the immune system not the same type of system as the digestive or circulatory systems?

A

It is not a collection of connected organs

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3
Q

Where are the cells of the immune system mostly found? [2 answers]

A

-in the blood
-in the lymph tissues (throughout the body)

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4
Q

What is the function of the immune system?

A

To kill all pathogens in the body

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4
Q

What is a leukocyte?

A

The collective term for white blood cells

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5
Q

What is an antigen?

A

A protein or glycoprotein embedded in the membrane of cells, that causes an immune response

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6
Q

In general, what do leukocytes do?

A

Respond to antigens

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7
Q

Why does the immune system not attack our own antigens (unless they are cancerous)?

A

It is capable of recognising the difference between self and non-self antigens

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8
Q

Fill in the gap : _____ from bacterial cells can also act as antigens

A

toxins

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9
Q

Fill in the gap: Antigens on the surface of our own cells are different from ____ or ______ _______

A

-pathogens
-transported tissues

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10
Q

What are all the cells in the immune systems derived from?

A

multipotent haematopoietic stem cells

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11
Q

Where are multipotent haematopoeietic stem cells found?

A

in the bone marrow

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12
Q

What two groups are multipotent haematopoietic stem cells classified into?

A
  • myeloid stem cells
  • lymphoid stem cells
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13
Q

What cells do myeloid stem cells produce? [two answers]

A
  • neutrophils
  • macrophages (which are derived from monocytes)
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14
Q

Which type of cell formed from a myeloid stem cell are macrophages derived from?

A

monocytes

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15
Q

Fill in the gap: All myeloid cells are _____

A

phagocytes

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16
Q

What do phagocytic cells do?

A

carry out the process of phagocytosis

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17
Q

What are some examples of cells that lymphoid stem cells produce? [two answers]

A
  • B lymphocytes (B cells)
  • T lymphocytes (T cells)
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18
Q

What are the two types of T lymphocytes (T cells) we need to know ?

A
  • Helper T Cells
  • Cytotoxic T cells
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19
Q

What are Helper T cells also known as?

A

CD4 cells

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20
Q

What are Cytotoxic T cells also known as?

A

CD8 cells

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21
Q

Where do B cells mature?

A

in the bone marrow

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22
Q

Where are B cells produced?

A

in the bone marrow

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23
Q

Where are T cells produced?

A

in the bone marrow

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24
Q

Where do T cells mature?

A

in the thymus gland

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25
Q

What is a primary lymphoid organ?

A

Where lymphocytes mature

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26
Q

What is a secondary lymphoid organ?

A

Where lymphocytes become activated to evoke an immune response

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27
Q

Where can lymphocytes be found? [2 answers]

A
  • circulating in the blood
  • in the lymphoid organs
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28
Q

What are the two primary lymphoid organs?

A
  • Bone marrow
  • Thymus
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29
Q

What are the three secondary lymphoid organs?

A
  • Spleen
  • Lymph nodes
  • Tonsils
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30
Q

What is toxigenesis?

A

The ability of bacteria to produce toxins

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31
Q

What are the two types of bacterial toxins?

A
  • endotoxins
  • exotoxins
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32
Q

Describe endotoxins: [3 points]

A
  • are lipopolysaccharides
  • cell associated
  • structural components of bacteria
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33
Q

Where are endotoxins released from?

A

parts of the cell wall

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34
Q

Where do endotoxins generally act?

A

in the vicinity of bacterial growth or presence

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35
Q

Where are exotoxins released from?

A

the inside of bacterial cells

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36
Q

Describe exotoxins: [2 points]

A
  • proteins
  • usually secreted by bacteria
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37
Q

Where do exotoxins generally act?

A

at tissue sites removed from the site of bacterial growth

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38
Q

What are some examples of exotoxins, and what effect do they have on humans? [3 answers]

A
  • Diptheria exotoxin –> inhibits protein synthesis , causing death of cells
  • Cholera exotoxin –> severe diarrhoea
  • Tetanus exotoxin –> inhibits neurotransmitters at synapses resulting in paralysis
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39
Q

What is a non-specific immune response?

A

Our immediate response to infection which is carried out in exactly the same way regardless of the pathogen (i.e. is not specific to a particular pathogen)

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40
Q

What leukocytes carry out the non-specific immune response?

A
  • macrophages
    OR
  • neutrophils
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41
Q

What are the non-specific physical barriers to pathogens? [6 answers]

A

-keratin in the cells of the skin makes it impermeable

-cilia, which are tiny hair-like structures that line the respiratory tract

-coughing

-vomiting

-sneezing

-mucus produced by the epithelial cells to trap microorganisms

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42
Q

What are the non-specific chemical barriers to pathogens? [4 answers]

A
  • sebum produced by the sebaceous glands in the skin, which has antimicrobial properties
  • hydrochloric acid secreted by cells lining the stomach wall
  • lactic acid produced by the bacteria in the vagina
  • the enzyme lysozyme founds in tears, saliva and mucus (hydrolyzes bacterial cell wall)
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43
Q

What are non-self molecules called?

A

antigens

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44
Q

What shape is a neutrophil’s nucleus?

A

lobed

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45
Q

Why does a neutrophil have a lobed nucleus?

A

this makes it easier for the neutrophil to squeeze between cells to reach infected tissues

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46
Q

What shape is a macrophage’s nucleus?

A

spherical

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47
Q

Are macrophages or neutrophils smaller?

A

neutrophils

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48
Q

How do neutrophils find pathogens?

A

they are carried around by the circulating blood until they reach an area of infected tissue, where they pass through the blood vessel wall and lodge in that tissue

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49
Q
A
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49
Q

Fill in the gaps: Bacteria and _____ tissues give off _______ which draw the neutrophils and ________ towards the area of infection

A
  • infected
  • substances
  • macrophages
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50
Q

Explain the process of phagocytosis [6 stages]

A

1) Pathogens produce chemicals that attract phagocytes.

2) Phagocytes recognise non-self antigens on the surface of the pathogen.

3) The phagocyte engulfs the pathogen with extensions of the cytoplasm called pseudopodia, to enclose the pathogen in a vacuole called a phagosome.

4) The membranes of the lysosomes readily fuse with the membrane of the phagosome, emptying the contents of lysosome into the phagosome

5) Enzymes from the lysosomes (e.g. lysozyme or protease) hydrolyse the molecules of the pathogen, killing it.

6) The products of the hydrolysis may be absorbed by the cell or released by exocytosis.

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51
Q

What do neutrophils do with the products of phagocytosis?

A

secrete the waste products by exocytosis

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52
Q

What do macrophages do with the products of phagocytosis?

A

Display the antigens of the pathogen in on the surface of their membrane, meaning the cell will now be an antigen-presenting cell, which can then be used to activate other parts of the immune system

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53
Q

What are lysosyzmes?

A

glycoside hydrolases

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54
Q

How do lysozymes kill bacteria?

A

they catalyse hydrolysis of beta 1-4 linkages which damages bacterial cell walls made of murein

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55
Q

Where can lysozyme be found? [6 answers]

A
  • tears
  • saliva
  • human milk
  • mucus
  • cytoplasmic granules (lysosomes) of macrophages
  • egg white
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56
Q

What is the cell mediated response?

A

An immune response which destroys one of your own body cells

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57
Q

What is the purpose of the cell mediated response? [2 reasons]

A
  • to kill cancerous cells
  • to kill your cells which have been infected by a pathogen
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58
Q

Are neutrophils long or short lived cells?

A
  • short lived
  • as they often use up so much energy during this process that they die shortly afterwards
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59
Q

Are macrophages long or short lived cells?

A

long lived cells

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60
Q

How does a macrophage become an antigen-presenting cell?

A
  • after a noncellular antigen has been phagocytosed by a macrophage, it is partially broken down into smaller fragments by enzymes in the macrophage
  • the resulting fragments bind to Major Histocompatibility Complex (MHC) proteins and the whole whole structure is displayed on the surface of the macrophage
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61
Q

Why does a cell become antigen-presenting?

A

labels the cell as infected, marking it as needing to be destroyed

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62
Q

How does a cell become cancerous?

A
  • has had one of more of its genes altered by a chemical, radiation or other factors
  • the altered genes called oncogenes code for proteins that are not normally found in the body, and can act as antibodies
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63
Q

What are T receptors?

A

Receptors for antigens

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64
Q

What is the structure of T cell receptors?

A
  • two chained proteins
  • have specific binding regions that differ from one cell to another
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65
Q

Why is the MHC needed?

A

T-cell receptors cannot bind to antigens on a self cell unless the antigen is first attached to the Major Histocompatibility Complex (MHC)

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66
Q

Where does activation of Helper-T cells take place?

A

In the secondary lymphoid organs

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67
Q

What must the Helper-T cell be activated by in the cell mediated response?

A

a macrophage

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68
Q

Describe the first section of the cell mediated response (Activation of Helper-T cells) : [10 stages]

A

1) There is a pathogen (bacteria or a virus) with antigens on its surface

2) The macrophage engulfs the pathogen by phagocytosis, and it will be then engulfed by a phagosome.

3) Lysosomes will fuse with the phagosome and digest the pathogen within the phagosome, using enzymes such as lysozyme

4) The macrophage uses its Major Histocompatibility Complex (MHC) to display antigens on its surface

5) There are antigen receptors on the Helper T cell (they all have the same tertiary structure, therefore the shame shape, so only bind to one specific presented antigen).

6) The antigens presented on the macrophage bind with the complementary receptor embedded in the membrane of the Helper T cell.

7) The bond is anchored as the CD4 receptor on the Cytotoxic T cell binds to the MHC itself.

8) The binding stimulates the Helper T cell to become activated, and it divides by mitosis (clonal expansion) to form Helper T memory cells, and Helper T effector cells

9)The effector Helper T cells secrete chemicals called cytokines, which activate Cytotoxic T cells

10) This causes the Cytotoxic T cells to divided to form effector Cytotoxic T cells and memory Cytotoxic T cells

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69
Q

Describe the second section of the cell mediated response (Activation of Cytotoxic-T cells) : [6 stages]

A

1) A pathogen infects a cell, making it a host cell

2) The infected cell presents the antigen of the pathogen on its surface, to become an antigen presenting cell. The antigens are presenting on the Major Histocompatibility Complex (MHC)

2) The effector Cytotoxic T cells bind to infected cells which are displaying the antigens complementary to the Cytotoxic T cell’s receptors.

3) The bond is anchored as the CD8 receptor on the Cytotoxic T cell binds to the MHC itself.

4) The cytotoxic T cell divides to produce memory Cytotoxic T cells, and effector Cytotoxic T cells (stimulated by cytokines from effector Helper T cells)

5) The effector Cytotoxic T cells releases chemicals (eg, perforin, which allows cytotoxic enzymes called granzymes to enter the infected cell) that cause pores to form in the effector cell

6) The infected cell undergoes apoptosis (programmed cell death), and is destroyed

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70
Q

What is humoral immunity?

A

Immunity which is active against toxins and free pathogens in body fluids

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71
Q

What are the two main body fluids (in the context of immunology) ?

A
  • lymph fluid
  • blood
72
Q

What are free pathogens?

A

Pathogens in the body that have not been ingested by phagocytes

73
Q

Which cells carry out the Humoral response?

A

B cells

74
Q

What are antibodies?

A

globular proteins known as immunoglobulins

75
Q

What are globular proteins

A

proteins with a roughly spherical tertiary structure (whereas fibrous proteins have a sheet-like tertiary structure)

76
Q

Is the binding site on an antibody an active site?

A

No - it is a receptor

77
Q

Fill in the gaps: ______ bind to _____ antigens on pathogens which have a ________ structure to their ______ site

A
  • antibodies
  • specific
  • complementary
  • binding
78
Q

What forms when an antibody binds to an antigen?

A

an antigen-antibody complex

79
Q

Why are all antibodies derived from one B-cell identical?

A

each B cell can only produce an antibody with one specific tertiary structure

80
Q

How is a massive variety of antibodies made in the humoral response if each B cell only produces one specific type of antigen?

A

Many different B cells are activated during the humoral response, each producing a different shaped antibody

81
Q

How many polypeptide chains is each antibody made up of?

A

4

82
Q

Why does an antibody have quaternary protein strucutre?

A

it is made up of more than one polypeptide chain (4 in fact)

83
Q

What are the polypeptide chains in an antibody held together by?

A

disulphide bonds/bridges

84
Q

What do all antibodies have on both their light and heavy chain?

A

constant regions

85
Q

Where is the light chain of the antibody?

A

joined to the heavy chain by a disulphide bridge at the top of the antibody (past the hinge region)

86
Q

Where are the variable regions of the antibody?

A

At the very top, where the binding site is

87
Q

What is the purpose of the hinge protein on an antibody?

A

to allow the antibody to bind to antigens that are different distances apart on the same pathogen

88
Q

Do all antibodies have the same constant region?

A

yes

89
Q

How do different antibodies have different binding sites?

A

they have a different amino acid sequence, causing the protein to have a different tertiary structure as it folds up in a very specific shape

90
Q

Which amino acid do disulphide bridges form between?

A

cysteine (Cys)

91
Q

What are the three ways in which antibodies can lead to the destruction of pathogens?

A
  • Opsonization
  • Agglutination
  • Neutralisation
92
Q

What does opsonization do to pathogens?

A

Coats pathogens with antibodies in order to increase their chance of being ingested by phagocytes

93
Q

What does agglutination do to pathogens?

A

Causes pathogens to become clumped together. Phagocytes can then engulf and digest lots of pathogens at the same time, which makes phagocytosis more efficient.

94
Q

What does neutralisation do to pathogens?

A

Antibodies neutralise toxins produced by bacteria, by binding to the toxin molecule

95
Q

Where do many of the bacteria that cause infectious disease in humans multiply?

A

in the spaces between cells (the extracellular cells of the body) rather than inside the cells themselves

96
Q

What response protects the extracellular spaces from pathogens?

A

the humoral response

97
Q

Roughly how many antibodies do plasma cells secrete per second?

A

2000

98
Q

Why are plasma cells the immediate defence (primary immune response) against infection

A

they only live a few days

99
Q

How long do memory cells live?

A

for decades

100
Q

Describe the humoral response: [7 stages]

A

1) The receptors on the B-lymphocyte bind to the complementary antigen on a pathogen, and engulf the pathogen by endocytosis.

2) The B cell internalises and hydrolyses, then presents fragments on the antigens on its surface using its Major Histocompatibility Complex (MHC) meaning it is now an antigen-presenting cell

3) The receptors on the Helper T cell binds to the antigen-presenting B lymphocyte (and are anchored by the CD4 receptor bonding to the MHC)

4) Cytokines are secreted by the helper T cell, which stimulates the B lymphocyte to divide by mitosis

5) During clonal expansion, memory cells takes place, which will display the complementary receptor to the antigen the humoral response is against

6) Effector cells have also formed, which divide again by mitosis and differentiate to form plasma cells

7) The plasma cells then secrete antibodies into body fluids to bind to complementary antigens on surface of pathogens

101
Q

What is the primary immune response?

A

The slow initial immune response when the body first encounters a specific antigen on a pathogen

102
Q

Why is the primary immune response slower?

A
  • maybe only one B cell has an antibody receptor that is specific to the shape of the antigen that has entered the body
103
Q

What is the secondary immune response?

A

When your body encounters the same antigen on the same pathogen a second time, the response is faster and creates higher concentrations of antibodies

104
Q

Why is the secondary immune response faster?

A

because you have memory cells for that specific antigen which divide to form plasma cells which can quickly secrete lots of antibodies

105
Q

Why do effective vaccines reduce the disease burden within the population?

A

As they offer protection to all members of society, even those who remain unvaccinated

106
Q

Fill in the gaps: As the number of individuals vaccinated in society declines, the protection of society against a disease _______

A

diminishes

107
Q

Why do illnesses spread again after vaccine scares?

A
  • vaccine scare
  • many parents stop vaccinating their children
  • number of unvaccinated children increases
  • initially these children are protected by herd immunity
  • as more children go unvaccinated, the virus has a larger pool of hosts within to multiply and spread
  • with the ‘free-ride’ protection diminishing, the unvaccinated children are now at risk of infection
108
Q

Explain clinical trials for vaccines

A

-To minimise any risk, vaccine development requires clinical trials
-The volunteers in clinical trials accept personal risk for the benefit of society
-Scientifically valid selection of populations is essential.
-There must be a reasonable chance of exposure to the disease, in order to evaluate the efficacy of the vaccine and the subject population must be sufficiently large for the trial results to be statistically valid.
-The subject population often consists of children, because vaccines are often developed to provide protection during, and beyond, childhood.

109
Q

What are the two types of immunity?

A
  • passive immunity
  • active immunity
110
Q

What is passive immunity?

A

immunity that is achieved when you are supplied with antibodies from an external source, rather than producing your own

111
Q

How can passive immunity be achieved?

A

as a foetus from the mother’s milk and passing across the placenta, or they can be directly injected (risk of killing these)

112
Q

What is active immunity?

A

the method in which the body is stimulated to produce its own immune response

113
Q

What type of immunity do vaccines provide?

A

active immunity

114
Q

How can active immunity be achieved?

A
  • can only be achieved by introducing an antigen into the body
  • this will activate the B-lymphocytes, causing them to produce memory cells
  • the memory cells divide by mitosis and differentiate into plasma cells to secrete antibodies faster and in greater quantities than during the primary response
115
Q

What must be maintained in antigens when they are introduced into the body by vaccination?

A

their tertiary structure

116
Q

What are the six different methods of vaccine that can be used?

A
  • dead pathogens
  • live pathogen
  • chemically modified toxins (toxoids)
  • antigens
  • inserting the genes for the antigens of the pathogen into a harmless microorganism
  • RNA vaccines
117
Q

What is a disadvantage of vaccines using dead pathogens?

A

they may only produce a few memory cells, so a booster is often required

118
Q

How do vaccines using live pathogens work?

A
  • Live pathogens which have been weakened so they no longer cause disease (attenuated pathogens) are injected
  • as these pathogens are still living they are able to reproduce and therefore stimulate a full immune response
119
Q

What are toxoids?

A

mild forms of the toxins produced by some bacteria

120
Q

How do antigen vaccines work?

A

the antigens from the virus are separated and injected

121
Q

Why does vaccination stimulate the humoral response but not the cell mediated response?

A

most methods inject antigens into the bloodstream so it does not enter the body cells

122
Q

What is a contagious disease?

A

A disease that is spread from person to person

123
Q

What is herd immunity?

A

Herd immunity occurs when a significant portion of a population becomes immune to an infectious disease and the risk of spread from person to person decreases; those who are not immune are indirectly protected because ongoing disease spread is very small

124
Q

Why does herd immunity not protect against all vaccine-preventable diseases?

A

some diseases are infectious but not contagious

125
Q

What is an infectious disease

A

A disease that is caught from pathogens in the environment

126
Q

Why will vaccinating most people against an infectious disease not create herd immunity?

A

no matter how many people are vaccinated, an unvaccinated individual is not protected by this as they can still contract the disease from pathogens in the environment

127
Q

Which people depend on herd immunity? [6 answers]

A
  • People without a fully-working immune system, including those without a working spleen
  • People on chemotherapy treatment whose immune system is weakened
  • People with HIV
  • Newborn babies who are too young to be vaccinated
  • Elderly people
  • Many of those who are very ill in hospital
128
Q

What is needed for herd immunity to work?

A

most people in the population must be vaccinated (for example, 19 out of every 20 people need to be vaccinated against measles to protect people who are not vaccinated)

129
Q

Which gives a higher level of individual protection, vaccination or herd immunity?

A

vaccination

130
Q

What are monoclonal antibodies?

A

antibodies with a highly specific binding site meaning they can only recognise and bind to a very unique and specific antigenic sequence.

131
Q

What produces monoclonal antibodies?

A

each specific monoclonal antibody is produced from one B cell

132
Q

Fill in the gap: Monoclonal antibodies for the same antigen are ________ to each other

A

identical

133
Q

Why are monoclonal antibodies often used in medicine?

A

because they bind very strongly to their complementary antigen

134
Q

Explain how monoclonal antibodies can be made for a specific antigen: [11 stages]

A

1) A mouse is exposed to an antigen that you want the antibody for

2) The B cells of the mouse produce lots of different antibodies to the antigen

3) The B cells are removed from the mouse’s spleen

4) The B cells are mixed with tumour cells that can divide outside the body (B-cells die quickly and can not divide outside the body, hence tumour cells being used)

5) Detergent is added that allows the cells to fuse.

6) The fused cells are separated (using a microscope).

7) Each B cell is allowed to divide by mitosis to make a clone of that cell.

8) Each clone is tested to see if it is making an antibody that is useful.

9) Any clone that is making an antibody that is useful can be grown on a large scale.

10) Each cloned B-cell will make just a single antibody – called a monoclonal antibody.

11)The monoclonal antibodies may be humanised (so that if they are injected into a person they will not be-rejected)

135
Q

What are some uses of monoclonal antibodies? [8 answers]

A
  • treating poisoning
  • cancer treatment
  • autoimmune therapies for allergic asthma, rheumatoid arthritis and Crohn’s disease
  • pregnancy tests
  • diagnosing HIV
  • detecting the presence of pathogens
  • detecting the presence of antibiotics in milk
  • location of blood clots for DVT
136
Q

How can monoclonal antibodies be used to treat cancer?

A
  • We can design monoclonal antibodies specific to these antigens, so that they can neutralise cancer cells as well as attracting cytotoxic T cells to kill the cancer cells using the cell mediated response
  • Or, we can attach anti-cancer drugs to the monoclonal antibodies
137
Q

How can monoclonal antibodies be used in autoimmune therapies?

A

they are able to bind to and deactivate factors involved in the inflammatory response

138
Q

What are four ethical problems with monoclonal antibodies?

A
  • have caused deaths when used as medicines
  • a particular monoclonal antibody used in phase 1 of a clinical trial caused multiple organ failures in healthy patients
  • production involves the use of mice and some people are opposed to animal testing (despite guidelines to minimise suffering)
  • transgenic mice can be used and some people are opposed to genetic engineering
139
Q

What are polyclonal antibodies?

A

antibodies with a diverse antigen binding site

140
Q

Why do polyclonal antibodies have a diverse antigen binding site even though they can only recognise a particular antigen?

A

they can bind to different variations of this particular antigen, such as the same antigen in a different species or mutant versions of the same antigen

141
Q

What does ELISA stand for?

A

enzyme-linked immunosorbent assay

142
Q

What is an ELISA test?

A

a common laboratory technique which is used to measure the concentrations of antibodies or antigens in a solution

143
Q

What does the ELISA test result in?

A

a coloured end product which correlates to the amount of analyte (antibody or antigen) present in the patient sample

144
Q

What are the advantages of an ELISA test? [3 answers]

A
  • simple and quick to carry out
  • produces quantitative results
  • can rapidly handle a large number of samples in parallel
145
Q

Describe how to carry out a positive direct ELISA to detect antigens: [11 steps]

A

1) Antibodies are absorbed to the ELISA plate well

2) The well is washed with cold buffer solution

3) The well is inverted to remove excess antibodies not absorbed to the wall of the well

4) The patient sample (eg, serum of the centrifuged blood/urine/mucus) is added to the well (complementary antigen binds to antibody)

5) The well is washed with cold buffer solution

6) The well is inverted to remove excess of the patient sample solution

7) A solution of enzyme-linked antibodies is added to the well

8) The well is washed with cold buffer solution

9) The well is inverted to remove any excess enzyme-linked antibodies

10) A complementary substrate solution is added to the well

11) A colour change will take place if the antigen you were testing for is present

146
Q

Describe how to carry out a positive indirect ELISA to detect antibodies? [10 steps]

A

1) Antigens are absorbed to the ELISA plate well

2) The well is washed with cold buffer solution

3) The well is inverted to remove excess antigens not absorbed to the wall of the well (complementary antibody binds to antigen)

3) The patient antiserum is added to the well

4) The well is washed with cold buffer solution

5) The well is inverted to remove excess of the patient antiserum

6) A solution of enzyme-linked anti-HISG is added to the well

7) The well is washed with cold buffer solution

8) The well is inverted to remove any excess enzyme-linked anti-HISG

9) A complementary substrate solution is added to the well

10) A colour change will take place if the antibody you were testing for is present

147
Q

What is anti-HISG?

A
  • anti guman immune serum globulin
  • it is the antibody against human antibodies
148
Q

Why is the solution used to wash the well in the ELISA test cold?

A

to ensure none of the organelles are damaged

149
Q

Why is the solution used to wash the well in the ELISA test a buffer?

A

so none of the enzymes denature due to changes in pH

150
Q

In the ELISA test (antigens), why is the well washed after adding the antibodies?

A

To remove any loose antibodies not bound to plastic wall, as when the patient sample was added, the antigens would bind to the loose antibodies which would then be washed out, leaving no antigen-antibody complexes and producing a false negative result

151
Q

In the ELISA test (antigens), why is the well washed after adding the patient sample?

A

To wash out excess of the patient sample solution otherwise the loose antigens would bind to the enzyme-linked antibody then be washed out in the next stage, producing a false negative result

152
Q

In the ELISA test (antigens), why is the well washed after adding the enzyme-linked antigens?

A

To wash out unbound enzyme linked antibodies, which would create a false positive if they bound to the substrate in the next stage.

153
Q

Why does HIV have a window period where it cannot be detected by the ELISA test? [3 points]

A
  • Delay in virus particle detection as the virus particle must first replicate
  • It takes time for your body to then produce antibodies against the HIV
  • Then, it can take up to 3 months for enough antibodies to be in the blood to be detected
154
Q

Explain how HIV causes replication of new virus particles: [11 steps]

A

1) The attachment proteins on the surface of the HIV virion bind to the receptors on the surface of the host cell.

2) The viral envelope of HIV fuses with the host cell membrane releasing the contents of the virus into the host cell.

3) Uses the enzyme reverse transcriptase as a template to manufacture dsDNA from ssRNA

4) The HIV dsDNA is inserted into the T-cell’s DNA.

5) Using the HIV enzyme called integrase.

6) The HIV DNA inside the host DNA is now called a provirus.

7) The HIV DNA is used to make HIV RNA ready for new virus particles. The process of making RNA from DNA is called transcription.

8) The RNA is also used to make HIV proteins e.g. capsid proteins and reverse transcriptase. The process of making protein from a RNA template is called translation.

9) These proteins are made on the host cells organelle called ribosomes.

10) The RNA and proteins assemble at the membrane of the host cell.

11) They are then released by budding off the membrane of the host cell.

155
Q

Fill in the gaps: A virus consists of a ______ acid surrounded by a ______ coat

A
  • nucleic
  • protein
156
Q

What is the structure of a virus? [5 points]

A

-capsid
-nucleic acid
-sometimes a viral envelope
-some contain enzymes
-some have attachment proteins

157
Q

What is the function of single stranded ribonucleic acid (ssRNA) in HIV?

A

It contains all the necessary information to synthesize all 15 proteins needed for replication and assembly of new virions in the infected host cells

158
Q

What is the viral envelope?

A

an outer lipid-protein layer

159
Q

In general, how does a virus infect a cell? [4 points]

A

-Proteins on the surface of the virus are complementary to specific proteins (or glycoproteins) on the surface membrane of a target cell

-For example, HIV attaches to a protein called CD4 found on the surface of T lymphocytes

-If a random collision is perfectly aligned, the viral protein binds to the protein or glycoprotein on the surface of the target cell

-The viral nucleic acid then enters the target cell

160
Q

What other features does HIV have that not all viruses do? [2 points]

A

-gp120 surface glycoproteins (attachment proteins) which bind to CD4 receptors

-the enzyme, reverse transcriptase

161
Q

What are the 4 main ways that the HIV virus enters the bloodstream?

A
  • by injecting into the bloodstream with needles/injecting equipment that’s been shared with other people
  • through the thin lining on or inside the anus, vagina and genitals
  • through the thin lining of the mouth and eyes
  • through cuts and sores in the skin
162
Q

What are ways that HIV can not be passed on? [9 points]

A
  • spitting
  • kissing
  • being bitten
  • contact with unbroken, healthy skin
  • being sneezed on
  • sharing baths, towels or cutlery
  • using the same toilets or swimming pools
  • mouth-to-mouth resuscitation
  • contact with animals or insects like mosquitoes
163
Q

What are the 5 bodily fluids that contain enough HIV to infect someone?

A

-semen
-vaginal fluids (including menstrual blood)
-breast milk
-blood
-lining inside the anus

164
Q

What does the nucleic acid once the host cell has been infected? [2 options]

A

Either:

-Becomes attached to the DNA of the host cell and remains dormant for a period of time (period of time is called latency)

OR

Takes over control of the host cell causing it to:
- replicate the virus
- produce new viral capsids
- assemble new virions
- release the new virions

165
Q

What are the features of a virus? [6 points]

A

-all viruses are pathogens
-all viruses are non-living
-viruses can only be replicated using the metabolism of another living cell called the host (in doing so they cause harm to the host cell)
-outside a suitable host cell, viruses are inert
-viruses are microscopic
-viruses have no metabolism of their own (eg, they do not use ATP and are unable to produce proteins)

166
Q

Fill in the gaps (HIV replication):

1) The _________ proteins on the surface of the HIV ________ bind to the _______ on the surface of the _______ cell.

2) The viral _______ of HIV fuses with the host cell ________ releasing the contents of the virus into the ______ cell.

3) The enzyme _______ __________

4) Uses HIV _________ to manufacture double stranded _______

5) The HIV_______ is inserted into the ______’s DNA.

6) Using the HIV enzyme called ________.

7) The HIV DNA inside the host DNA is now called a ________.

8) The HIV DNA is used to make HIV _______ ready for new virus particles. The process of making RNA from DNA is called _________.

9) The RNA is also used to make HIV ________ e.g.______ proteins and reverse transcriptase. The process of making protein from a RNA _______ is called ________.

10) These proteins are made on the host cells organelle called _______.

11) The RNA and_____ assemble at the_______ of the host cell.

12) They are then released by_____ off the membrane of the host cell.

A

1) attachment, virion, receptors, host
2) envelope, membrane, host
3) reverse transcriptase
4) ssRNA, DNA
5) dsDNA, T-Cell
6) integrase
7) provirus
8) RNA, transcription
9) proteins, capsid, template, translation
10) ribosomes
11) proteins, membrane
12) budding

167
Q

Without medical intervention, what does HIV usually result in?

A

AIDS (acquired immunodeficiency syndrome)

168
Q

What is the function of the enzyme reverse transcriptase in HIV?

A

Provides a template to manufacture dsDNA from ssRNA

169
Q

What is the function of the enzyme integrase in HIV?

A

Inserts the viral DNA into the host cell’s DNA

170
Q

Fill in the gap : HIV virus uses the reverse transcriptase enzyme as a template to ________ dsDNA from ssRNA

A

manufacture

171
Q

What is a mature virus particle called?

A

a virion

172
Q

What is the function of the attachment protein (surface glycoprotein) in HIV?

A

Binds to the CD4 receptor on the target Helper T-cell

173
Q

What is the capsid in a vrius?

A

the protein coat

174
Q

What cells does HIV infect?

A

Helper T-Cells (AKA CD4 cells)

175
Q

What 3 bodily fluids don’t contain enough of the HIV virus to infect another person?

A
  • saliva
  • sweat
  • urine
176
Q

What is a virion capable of doing?

A

infecting a host cell

177
Q

From infection with HIV to the development of AIDS, roughly how many years go by and what symptoms does the person have?

A

-usually around 10 years go by
-person feels well (but w/o use of antiviral drugs, will be able to transmit the virus to other people)

178
Q

What will the virion do inside the host cell?

A

replicate and then the mature virions will leave the cell, killing the infected cell in the process

AQA A Level Biology (2 decks)

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