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A Level Biology Edexcel A > Immunity, Infection & Forensics > Flashcards

Immunity, Infection & Forensics Flashcards

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6
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What are the 4 shapes of bacteria?

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  • cocci
  • vibrios
  • bacilli
  • spirilla
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7
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What are the 2 types of bacteria?

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  • Gram positive bacteria
  • Gram negative bacteria
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8
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What is lipopolysaccharide (LPS)?

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Important outer membrane component of gram negative bacteria.

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9
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How does LPS affect staining of bacteria?

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LPS is an endotoxin: it blocks antibiotics, dyes and detergents so it protects the thin inner membrane and cell wall of gram negative bacteria. Makes them resistant to pencilin and lysosome.

Gram negative bacteria reject stain so remain pink.
Gram positive bacteria take up stain so turn purple.

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10
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Give the name for asexual bacteria reproduction.

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Binary fission

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11
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Describe binary fission.

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  • Bacteria reaches a certain size
  • DNA is replicated
  • Old cell wall begins to break down around middle of cell
  • DNA is associated with cell membrane. Cell pinches together forming a septum
  • Two new identical daughter cells are formed. Plasmids often divide at the same time
  • time between the divisions is the Generation Time
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12
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What are the 3 forms of bacterial sexual reproduction?

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  • Transformation
  • Transduction
  • Conjugation

Horizontal gene transfer

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13
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Describe Transformation

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A short piece of DNA is released by a donor (which does not need to be alive) or the DNA is in the ‘environment’. This is actively taken up by the recipients. The new DNA replaces a similar piece of DNA in the recipient.

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14
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Describe Transduction

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A small amount of DNA is transferred from one bacterium to another by a bacteriophage.

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15
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Describe Conjugation

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Plasmid DNA is transferred from one bacterium to another by direct contact. The donor cells (F+) produces a sex pilus. A cytoplasmic bridge is created to the recipient cell (F-). DNA is transferred through the pilus.

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16
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What are viruses?

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Small organic particles with a structure that is quite different from that of bacteria and much simpler.

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17
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What do viruses consist of?

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They consist of a strand of nucleic acid (DNA or RNA) enclosed within a protein coat (capsid). Viral DNA can be single or double stranded.

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18
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Describe viral replication

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  1. Virus attaches to host cell
  2. Virus inserts nucleic acid
  3. Viral nucleic acids replicate
  4. Viral protein coats synthesised
  5. New virus particles formed
  6. Virus particles released due to cell lysis
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19
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Describe the conseqence of viral replication cell lysis to host cell.

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It kills the host cells and it results in cell contents e.g. enzymes and other chemicals being released damaging neighbouring cells. This can result in the disease symptoms produced by the viral infection.

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20
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Describe the viral envelope.

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Some viruses have an outer envelope taken from the host cell’s surface membrane so contains lipids and proteins. It also has glycoproteins from the virus itself which are antigens - helpps virus attacgh to cell and penetrate the surface membrane.

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21
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What are the two pathways for viral reproduction.

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  • Lytic pathway
  • Lysogenic pathway
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22
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Describe the lytic pathway.

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  • Viral genetic material is replicated independtly of the host DNA straight after entering the host cell.
  • Mature viruses are made by the host cell
  • Cell bursts and releases large numbers of new virus particles
  • These go on to invade other host cells
  • The virus is said to be vilurent (disease causing)
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23
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Describe the lysogenic pathway.

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  • Viruses are non-virulent when they first get into the host cell
  • They insert their DNA into the host DNA so it is replicated every time the host cell divides
  • No mRNA is produced from viral DNA because one of the viral genes causes the production of a repressor protein.
  • This makes it impossible to translate the rest of the viral genetic material.
  • The virus remains dormant and becomes lytic and therefore virulent under the right conditions.
24
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Give the 4 major entry routes of pathogens into the body.

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  1. Cuts in the skin
  2. Through the digestive system via contaminated food or drink
  3. Through the respiratory system by being inhaled
  4. Through other mucosal surfaces e.g. inside of nose, mouth, genitals.
25
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List the major transmission routes of pathogens into the body.

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  • Inhalation
  • Direct Contact
  • Inoculation
  • Vectors
  • Ingestion
  • Fomites
26
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Describe inhalation as a transmission route.

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Breathing in of lipid droplets containing the pathogen which were previously expelled from a respiratory tract (e.g. by cough/ sneeze).

27
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Describe direct contact as a transmission route.

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Can occur from sharing needles, unprotected sex, direct blood-to-blood transfer through cuts and grazes, maternal transmission from mother to unborn child in breast milk.

28
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Describe inoculation as a transmission route.

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Pathogens enter the body directly through a break in the skin e.g. dog bite, tattooing, infected needle.

29
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Describe vectors as a transmission route.

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A living organism that transmits infection from one host to another e.g. mosquito’s - malaria.

30
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Describe ingestion as a transmisssion route.

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Consuming contaminated food or drink leads to vomiting and diarrhoea. Greatest risk from raw/ undercooked food.

31
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Describe fomites as a trnasmission route.

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Inanimate objects that carry pathogens from one host to another. e.g. hospital bedding, towels.

32
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Describe the skin as a barrier from infection.

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Contaiins the tough protein keratin, however the skin can be breached by wounds. Blood clotting prevents this. Skin flora outcompetes and prevents colonisation by other bacteria.

33
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Descirbe the mucosal membranes as a barrier from infection.

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Line the airways and the gut. The mucus traps microbes and other particles. Beating cilia carry the mucus up to the throat to be swallowed. Secretions from eyes & nose contain the enzyme lysozyme that breaks down bacterial cell walls causing them to burst.

34
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Describe stomach acid as a barrier to infection.

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Contains hydrochloric acid, giving a pH of less than 2.0. This kills most bacteria that enter with food or drink. This is also the optimum pH for the digestive enzyme pepsin.

35
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Describe the gut flora as a barrier to infection.

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Beneficial bacteria found in both intestines. We have a mutualistic relationship with them. They aid digestion and outcompete pathogenic bacteria for food and space - competiviely exclude pathigenic bacteria. The bacteria also secrete chemicals (lactic acid) to aid the defence against pathogens.

36
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What 2 things can happen when bacteria get into the body?

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  1. They grow in a localised area
  2. Get into the blood supply and get carried around the body
37
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How do bacteria make people unwell?

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Through the toxins bacteria produce either as by-products of their metabolism or part of their parasitic lifestyle to incapacitate their host or its immune response.

38
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2 types of toxins?

A
  • Endotoxins
  • Exotoxins
39
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Describe endotoxins.

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  • Lipopolysaccahride part of outer layer of gram negative bacteria. Released on the death of bacteria.
  • Rarely fatal
  • Tend to cause symptoms such as fever, vomiting and diarrhoea
  • The symptoms can indirectly lead to detah e.g. by dehydration
40
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Describe exotoxins.

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  • Soluble proteins
  • Produced and released into the body by bacteria as they metabolise and reproduce. Stronger ability to trigger an immune response
  • Rarely cause fever
  • Responsible for some of the most dangerous and fatal bacterial diseases
41
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Describe what is meant by the non-specific immune response and its purpose.

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  • Response that is effective against wide range of infectious agents/ pathogens
  • Does not involve recognition of pathogen
  • Does not react to specific antigens (memory cells not present)

To destroy, prevent the multiplication and spread of invading pathogens.

42
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Give the 4 main processes of the non-specific immune response.

A
  1. Lysozyme action (secretions in the mouth, eyes, nose)
  2. Inflammation (release of histamine)
  3. Interferon (anti-microbial proteins)
  4. Phagocytosis
43
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What is the purpose of inflammation?

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To destroy the cause of infection and remove it and its products from the body. If this fails to limit the spread of infection, widepsread infection leading to septic shock (sepsis) occurs.

44
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Describe inflammation/ inflammatory response.

A
  1. Damage/ infection causes damaged mast cells and basophils to release histamine in response to the recognition of antigens on the surface of a pathogen.
  2. Histamine causes the vasodilation of arterioles nearby so increases blood flow to the area.
  3. Histamine also causes the capillaries to increase their permeability so vessels leak.
  4. So plasma fluid, white blood cells and antibodies leak from the blood to site of infection - oedema.
  5. WBC begin to destroy pathogen.
  6. Interleukin is released from WBC and attracts more phagocytic cells to site of infection.
  7. Neutrophils can destroy bacteria.
  8. Monocytes will move into site and differentiate into macrophages which engulf dead neutrohils, bacteria, cell debris.
  9. Pus will collect at the site (made up of dead WBC)
  10. The pus will break down and be absorbed by the surrounding tissue.
45
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What is histamine?

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An amine which is involved in inflammatory response to infection.

46
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What is interleukin?

A

Protein which regulates inflammation.

47
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Describe the appearance of inflammation.

A
  • Red
  • Swollen (oedema)
  • Painful
  • Warm
48
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Describe lysozyme action.

A

An antibacterial enzyme that degrades the peptidoglycan found in bacterial cell wall causing cells to swell and burst. Found in tears, nasal secretion and saliva.

49
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Describe the action of Interferon.

A

Provides defence against viruses (but also some bacteria and protozoa).
Released from infected cells. It binds to surrounding cell surface receptors preventing viral protein synthesis and therefore replication of new viral particles. So virus cannot infect more cells.

50
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Describe phagocytosis.

A
  1. Bacterium binds to receptors on macrophage surface and psueodpodia surround the bacterium
  2. Bacterium is engulfed by macrophage into a phagosome.
  3. Lysosome containing digestive enzymes binds to phagosome forming phagolysosome.
  4. Bacterium is digested
  5. A small vacuole containing some fragments of the bacterium buds off from the phagolysosome
  6. Phagolysosome fuses with cell surface membrane and contents are released by exocytosis. Within the small vacuole, a bacterial fragment is bound to an MHC protein.
  7. Vacuole fuses with cell curface membrane and bacterial fragment is presented on the macrophage cell membrane as an antigen.
  8. Macrophage has now bcome an APC - specific immune response can now begin.
51
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Describe the white blood cells

A

White blood cells also known as leucocytes.
Neutrophils -> for non specific:
* 70% of WBCs
* Ingest and destroy bacteria (5-20 in phagocytosis)
* Last only a few days

Lymphocytes -> specific:
* 2 types - T cells and B cells
* B cells produce antibodies
* Some last few days, others years

Monocytes & Macrophages -> both
* Monocytes circulate in the blood and move into tissue and differentiate into macrophages
* Macrophages engulf bacteria, foreugn matter and cell debris in phagocytosis. Macrophages will present antigen to lymphocytes.

Eosinophils & Basophils
* Granular cytoplasm
* Basophils produce histamine

52
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What does APC represent?

A

Antigen-presenting cell

53
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What does MHC represent?

A

Major Histocompability protein

54
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Give the 4 characteristics of specific immune response.

A
  1. It can distinguish self from non-self
  2. It is specific
  3. It is diverse - can recognise many different antigens
  4. It has immunological memory (memory cells)
55
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What is an antigen?

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A molecule (usually protein or polysaccharide) found on the surface of cells or particles. It is recognised by immune system cells as non-self and activates/initiates an immune response.

56
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Describe the primary immune response.

A

Occurs when the body meets a specific pathogen for the first time.

The Humoral Response:
* T helper and T memory cells are created
* B effector cells and B memory cells are created
* B effector cells differentiate into plasma cells to produce antibodies

The Cell Mediated Response:
* T killer cells are involved

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A Level Biology Edexcel A (9 decks)

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