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Biology unit 6 > Disease and Defence > Flashcards

Disease and Defence Flashcards

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1
Q

Why are viruses classified as non-living?

A

They are acellular. No cytoplasm, no metabolism and can’t self-replicate

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2
Q

Name 3 types of virus and give examples

A

DNA virus - lambda phage
RNA virus - Ebola
RNA retrovirus - HIV

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3
Q

Describe Ebola

A

Caused by the Ebola virus. Spread by direct contact with infected body fluids. Symptoms include fever, vomiting, diarrhea and internal bleeding.

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4
Q

What virus causes Ebola?

A

Can be caused by different viruses, all members of the Ebolavirus genus which is part of the filoviridae (filament shaped) family of viruses.

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5
Q

Compare and contrast the tobacco mosaic virus and Ebola.

A

Both are RNA viruses. Tobacco mosaic virus contains ssRNA, which can be directly translated into proteins by ribosomes. Ebola contains negative ssRNA, which needs to be transcribed to produce mRNA before translation.

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6
Q

How does the tobacco mosaic virus cause disease?

A

It affects plants, mainly transmitted via infected sap. Contains ssRNA, which is directly transcribed by host cell to create new virions. Virions enter other cells via plasmodesmata. Causes stunted growth and mottled leaves.

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7
Q

What is tuberculosis?

A

A bacterial disease caused by Mycobacterium tuberculosis and M. bovis. It damages the lymph nodes in the lungs and neck, and weakens the immune system.

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8
Q

How is tuberculosis transmitted?

A

Airborne droplet transmission

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9
Q

What is the lambda phage virus?

A

A type of bacteriophage virus which infects E.coli bacteria.

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10
Q

Describe the general structure of a lambda phage virus.

A

It has a head and tail region. The head contains a double stranded DNA genome. The tail facilitates attachment and the insertion of viral DNA into the bacterium.

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11
Q

Describe the lysogenic pathway.

A
  1. non-virulent viruses inject DNA into host cell DNA as provirus. Viral DNA replicates when host cell divides.
  2. Virus produces repressor proteins to inhibit transcription
  3. Latent virus enters the lytic pathway when host cell is damaged or immune system weakens.
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12
Q

Describe the lytic cycle

A
  1. Virulent viruses inject nucleic acid into host cell cytoplasm. Viral genetic information replicates immediately, independently of host cell DNA.
  2. Many virions assemble, causing cell lysis
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13
Q

Describe HIV

A

Caused by human immunodeficiency virus,
Spread by direct contact with infected body fluids. Destroys white blood cells making the individual immunodeficient and increasingly susceptible to other diseases. Leads to AIDS.

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14
Q

How does HIV result in the symptoms of AIDS?

A
  1. Attachment proteins bind to complementary CD4
    receptor on TH cells
  2. HIV particles replicate inside TH cells, killing or damaging
    them
  3. AIDS develops when there are too few TH cells for the
    immune system to function
  4. Individuals cannot destroy other pathogens and suffer
    from secondary diseases/ infections. May cause death
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15
Q

What is the latency period?

A

The period of time following infection before symptoms appear.

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16
Q

What is a pathogenic organism?

A

An organism that has the ability to cause damage to the host.

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17
Q

Give 4 major routes of infection in humans.

A

-Droplet infection (coughing/sneezing)
-Direct contact (skin to skin or bodily fluids)
-Oral (ingesting contaminated food/drink)
-Airborne (small infected particles travel in the air)

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18
Q

What is indirect transmission?

A

Transmission which requires a vector intermediate

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19
Q

Outline the natural defenses in the body that reduce the risk of infection

A

Skin, skin flora, blood clotting, lysosomes, hydrochloric acid, mucus membranes, phagocytosis, inflammation

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20
Q

What are skin flora?

A

Microorganisms which naturally live on the skin. They are usually harmless to humans but act as a useful defense against pathogens.

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21
Q

How do skin flora help to prevent infection?

A

They compete with pathogenic microorganisms for resources and nutrients. This hinders growth of harmful microorganism colonies.

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22
Q

What are non-specific immune responses?

A

Defenses which don’t target a single type of antigen or pathogen, but a wide range of different pathogens. Examples include inflammation and phagocytosis.

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23
Q

Name 4 ways the nonspecific immune system responds to infection.

A

-inflammation
-phagocytosis
-digestive action of lysosomes
-production of interferon (antiviral agent)

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24
Q

What are interferons?

A

A type of signaling molecule involved in the non-specific immune response. It’s secreted by virus infected cells to alert nearby cells and activate immune cells.

25
Q

Outline the process of phagocytosis.

A
  1. Phagocyte moves towards pathogen via chemotaxis
  2. Phagocyte engulfs pathogen via endocytosis to form
    a phagosome
  3. Phagosome fuses with lysosome (phagolysosome)
  4. Lysozymes digest pathogen
  5. Phagocyte absorbs the products from pathogen
    hydrolysis
26
Q

What are lysosomes?

A

Digestive enzymes. Often found in secretions like tears and mucus. They damage bacterial cell walls, causing osmotic lysis

27
Q

Outline the general process of inflammation.

A
  1. Damaged vessels release histamines, causing vasodilation.
  2. Blood flow & permeability of blood vessels increase.
  3. White blood cells & plasma enter the infected tissue.
28
Q

Explain the role of antigen-presenting cells (APCs)

A

Macrophage displays antigen from pathogen on its surface (after hydrolysis and phagocytosis). Enhances recognition by T helper cells, which can’t directly interface with pathogens(antigens in body fluid.

29
Q

What are antibodies?

A

Y-shaped proteins which are secreted by plasma cells. They bind complementarity to antigens on pathogens and aid in the specific immune response.

30
Q

Describe the structure of antibodies.

A

Quaternary structure, 2 light chains held by disulfide bridges and 2 longer heavy chains. Binding sites on variable region of light chains have specific tertiary structure complementary to an antigen and the rest of the molecule is the constant region.

31
Q

How do antibodies lead to the destruction of a pathogen?

Which processes

A

-Formation of antigen-antibody complex results in agglutination
-Activation of complement
-Opsonization (marks microbes for phagocytes)
-Precipitation/neutralization (makes toxins insoluble)

32
Q

What is an antigen?

A
  • Cell-surface molecule can stimulate immune response
  • Usually (glyco)protein, sometimes (glyco)lipid or
    polysaccharide
  • Immune system recognises as “self” or “non-self” =
    enables identification of cells from other organisms of
    same species, pathogens, toxins & abnormal body
    cells
33
Q

What are antigen presenting cells (APCs)?

A

Any type of immune cell which displays parts of a pathogen (antigens) on its surface to elicit an immune response.

34
Q

What are plasma cells?

A

A type of full matured and differentiated B-lymphocyte which produces a specific antibody.

35
Q

Name the two types of specific immune response.

A

Cell- mediated and humoral.

36
Q

name the two main types of
B-lymphocyte.

A

-B memory cell
-B effector cell

37
Q

Name the 3 main types of
T-lymphocyte

A

-T killer cell
-T helper cell
-T memory cell

38
Q

Outline the process of the cell-mediated response

A

Complementary Th lymphocytes bind to foreign antigen on APC. Stimulates:
-clonal expansion of complementary T helper cells, which become memory cells or trigger humoral response
-clonal expansion of T killer cells: secrete perforin to destroy infected cells.

39
Q

What is clonal selection?

A

A specific antigen activates a certain B cell by binding to a unique and highly specific receptor on the B lymphocytes. This causes it to undergo cell division to produce many identical clones.

40
Q

What is clonal expansion?

A

T/B cells that are complementary go an antigen undergo rapid mitotic division to form many cloned cells.

41
Q

Outline the process of the humoral response.

A
  1. Complementary TH

lymphocytes bind to foreign

antigen on antigen-presenting T cells
2. Release cytokines that stimulate clonal expansion
of complementary B lymphocytes
3. B cells differentiate into plasma cells
4. Plasma cells secrete antibodies with complementary variable region to antigen.

42
Q

What is the function of T and B memory cells?

A

They remain in the body for a long time following an infection and provide long-term immunity. If the same pathogen is encountered in the future, they can divide rapidly to provide an effective secondary immune response.

43
Q

What is the function of T helper cells?

A

They regulate the adaptive immune response through the release of cell signaling molecules called cytokines. They activate many effector cells in the adaptive immune system like T killer cells and B lymphocytes.

44
Q

What is the function of T killer cells?

A

They introduce apoptosis (programmed cell death) in virus infected, damaged or cancerous cells.

45
Q

Compare the primary and secondary immune responses.

A

Primary: initial response when a pathogen is first encountered. A small number of antibodies are produced slowly.
Secondary: pathogen encountered for a 2,3,4, etc time. Immunological memory gives a rapid production of a large number of antibodies.

46
Q

What is happening during the latent period of the primary immune response?

A

Antigen-presenting cells carrying out phagocytosis, T helper cells detect antigens and secrete cytokines, proliferation and differentiation of specific B and T cells.

47
Q

Define active immunity

A

Resistance in an organism that has developed through the production of specific antibodies in response to a pathogen. It provides
long-lasting immunity as memory cells are produced.

48
Q

What are the 2 types of active immunity?

A

-Natural active immunity (after infection)
-Artificial active immunity (after exposure to a weakened or dead pathogen)

49
Q

Give an example of artificial active immunity

A

Vaccination against rubella.

50
Q

How do vaccinations that use antigens provide long-lasting immunity?

A

● Antigens in vaccine trigger primary immune
response without infection

● If a pathogen is encountered, secondary immune
response destroys the pathogen before symptoms
develop

51
Q

Define passive immunity

A

Resistance in an organism acquired via the transfer of antibodies. It provides short-term immunity as no memory cells are produced.

52
Q

What are the two types of passive immunity?

A

Natural (acquired by an infant when antibodies are transferred through the placenta and colostrum from the mother)
Artificial (acquired from the administration of specific antibodies from another organism)

53
Q

Give an example of artificial passive immunity

A

Treatment of rabies

54
Q

How do vaccinations that use antibodies provide short-term immunity?

A

Antibodies give rapid protection against a harmful microorganism. It allows time for the development of an active immune response.

55
Q

Why is there an ‘evolutionary race’ between pathogens and their host?

A

Host defenses are selection pressure for bacteria. Random genetic mutations may enable bacteria to evade these defenses.
Hosts with phylogenetic characteristics that reduce likelihood & symptoms of infection have a selective advantage.

56
Q

What are bactericidal antibiotics?

A

Antibiotics which kill bacteria by inhibiting major metabolic processes and biosynthesis pathways.

57
Q

What are bacteriostatic antibiotics?

A

A class of antibiotics which prevent bacteria from growing by interfering with processes required for their growth like metabolism or DNA replication.

58
Q

How do hospitals minimize the spread of bacteria?

A

-screening and quarantine of affected patients
-hygiene code of practice
-antibiotics prescribed only when necessary and course completed to minimize selection pressure.

Biology unit 6 (3 decks)

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