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

Immunity, Infection & Forensics Flashcards

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1
Q

What are the 4 shapes of bacteria?

A
  • cocci
  • vibrios
  • bacilli
  • spirilla
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2
Q

What are the 2 types of bacteria?

A
  • Gram positive bacteria
  • Gram negative bacteria
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3
Q

What is lipopolysaccharide (LPS)?

A

Important outer membrane component of gram negative bacteria.

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4
Q

How does LPS affect staining of bacteria?

A

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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5
Q

Give the name for asexual bacteria reproduction.

A

Binary fission

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6
Q

Describe binary fission.

A
  • 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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7
Q

What are the 3 forms of bacterial sexual reproduction?

A
  • Transformation
  • Transduction
  • Conjugation

Horizontal gene transfer

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8
Q

Describe Transformation

A

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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9
Q

Describe Transduction

A

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

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10
Q

Describe Conjugation

A

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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11
Q

What are viruses?

A

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

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12
Q

What do viruses consist of?

A

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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13
Q

Describe viral replication

A
  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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14
Q

Describe the conseqence of viral replication cell lysis to host cell.

A

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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15
Q

Describe the viral envelope.

A

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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16
Q

What are the two pathways for viral reproduction.

A
  • Lytic pathway
  • Lysogenic pathway
17
Q

Describe the lytic pathway.

A
  • 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)
18
Q

Describe the lysogenic pathway.

A
  • 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.
19
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23
Q

Describe what is meant by the non-specific immune response.

A
  • Response that is effective against wide range of infectious agents/ pathogens
  • Does not involve recognition of infectious agent
  • Does not react to specific antigens

To destroy, prevent the multiplication and spread of pathogens.

24
Q

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
25
Q

Describe inflammation/ inflammatory response.

A
  1. Damge/ 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 teh 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.
26
Q

Describe the appearance of inflammation.

A
  • Red
  • Swollen (oedema)
  • Painful
  • Warm
27
Q

Describe lysozyme action.

A
28
Q

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.

29
Q

Describe phagocytosis.

A
  1. Bacterium binds to receports 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.
30
Q

What does APC stand for?

A

Antigen-presenting cell

A Level Biology Edexcel A (9 decks)

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