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Infection and Immunity > 17 Bacterial Cell Structure > Flashcards

17 Bacterial Cell Structure Flashcards

1
Q

what do macrophage attracting neutrophils (monocytes) secrete

A

IL-1-beta
TNF-alpha
IL6

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2
Q

what are bacteria

A

simple prokaryotic structure

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3
Q

where is the DNA in bacteria

A

DNA free in cytoplasm

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4
Q

what do some bacteria have that the immune system recognise

A

some bacteria have extra layers outside cell wall (recognised by immune system and not eukaryote-like)

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5
Q

what are prokaryotes the size of

A

size of a mitochondrion in eukaryote

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6
Q

where can pathogenic bacteria live/replicate

A

pathogenic bacteria can live/replicate inside eukaryotes

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7
Q

what are bacteria often named for

A

characteristic shapes due to their cell wall and cytoskeleton structures

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8
Q

sphere bacteria example

A

streptococci

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9
Q

rod bacteria example

A

Bacillus anthracis

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10
Q

spiral bacteria example

A

Aquaspirillum

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11
Q

spirochetes bacteria example

A

borrelia

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12
Q

what is borrelia like

A

very thin, flexible wavy shaped spirochetes, immune evasion and cause disease

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13
Q

no cell wall bacteria example

A

mycoplasma

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14
Q

what is mycoplasma like

A

no wall so can live inside human cells and the body without giving cell wall signals

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15
Q

what is cell shape associated with

A

walls which give strength and robustness to bursting

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16
Q

why is bacterial surface structures important

A

Major surface contact points between bacteria and the immune system
Important functional structures in commensal and pathogenic bacteria

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17
Q

why do bacterial surface structures change

A

vary structures to evade immune recognition

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18
Q

how do we examine bacteria

A

Simple microscopic staining of bacteria and examination with a light microscope reveals their morphology (µm scale)

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19
Q

how do we examine bacteria to high resolution

A

high resolution of surface structures like flagella (nm scale) you need electron microscopy and negative staining with electron dense materials

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20
Q

why does DNA leak from bacteria

A

DNA in cytoplasmic membrane of prokaryotes (easily leaks out if cell burst), wall prevents bursting, many Gram-negative bacteria have an extra outer membrane and structures beyond the wall

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21
Q

what is bacterium structures encoded from

A

Every structure of the bacterium is encoded from its DNA

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22
Q

how does bacteria and human DNA differ

A

DNA of bacteria has different codon usages to humans and is differently modified (acetylated/methylated)

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23
Q

what is bacteria like in humans an animals

A

immunogenic

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24
Q

what is the gram+ve membrane like

A

Gram +ve bacterial have the single membrane and cell wall and Gram negative have an extra outer membrane

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25
Q

gram +ve stain

A

purple, retain first stain in the process in their thick cell walls

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26
Q

gram -ve stain

A

pink, lose first dark purple stain from their thinner cell walls when alcohol is added (going colourless), but then get re-stained by the pink second stain

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27
Q

what are bacterial cell walls important for

A

resist large osmotic pressure on cell membrane due to high internal solute concentration in cytoplasm

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28
Q

what do eubacteria cell walls consist of

A

PG – which is made of N-acetylglucosamine (G) and N-acetylmuramic acid (M), small group of amino-acids L-alanine, D-alanine, D-glutamate, and either L-lysine or DAP

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29
Q

what is PG sheet made of

A

chains of alternating M and G molecules cross-linked by the amino-acids to form a rigid sheet

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30
Q

Typical cell wall peptidoglycan structure in Gram negative bacteria

A

Peptidoglycan contains two N acetyl sugars and D & L amino-acids and is immunogenic and sensed by hosts

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31
Q

what can macrophage WBC make

A

Macrophage white blood cells can also be stimulated to produce lysozyme and kill intracellular bacteria

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32
Q

gram +ve bacteria example

A

Bacillus

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33
Q

gram +ve cell wall

A

thick and consist of 90% peptidoglycan, and 10% teichoic acid, this is negatively charged and gives the outside of the bacterial cell a net negative charge

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34
Q

gram -ve bacteria example

A

Salmonella

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35
Q

gram -ve cell walls

A

thin with no teichoic acids, they are connected to outer membrane by Braun’s lipo-protein

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36
Q

where is the gram -ve outer membrane

A

Outside cell wall in Gram-negative bacteria (special mycomembrane exists outside some Gram-positive bacteria such as Mycobacteria which cause TB)

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37
Q

what is the gram -ve outer membrane

A

lipid bilayer, only inner leaflet is solely phospholipid, outer leaflet is lipopolysaccharide (LPS)

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38
Q

what does the LPS consist of

A

hydrophobic Lipid A tails bound to a sugar core made up of heptose and KDO, this is bound to a long hydrophilic carbohydrate chain, O antigen which sticks out into the medium

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39
Q

what is the o antigen like

A

hydrophilic, excludes hydrophobic compounds from getting close to bacteria

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40
Q

where is LPS

A

only in nature in bacteria

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41
Q

what is LPS like

A

highly toxic to humans and sensed by them

endotoxin - only released when bacterial cells lyse

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42
Q

what is needed in gram -ve outer membrane

A

Because it is a membrane, special channels needed for materials to get in and out of cells - porins

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43
Q

what are porins

A

proteins in circular groups spanning membrane, form pores allowing molecules of certain size to pass into periplasm

44
Q

when do porins open/close

A

in response to osmotic conditions

45
Q

what are some porins sensed by

A

host immune system

46
Q

how is final LPS made

A

by a series of enzymes that the bacteria can acquire or have extra genes for to vary it

47
Q

where is the periplasm

A

compartment between inner and outer membranes of Gram-negative bacteria

48
Q

how much of the cell does the periplasm take up

A

20-40% of the total cell volume

49
Q

what does the periplasm contain

A

thin peptidoglycan wall and many proteins

50
Q

what is effected by the LPS core sugar diversity in E.coli

A

Changes immune recognition

O polysaccharide/ O antigen also varies greatly or is absent, again changing immune recognition

51
Q

what do the periplasmic proteins bind

A

Binding proteins for amino-acids, sugars, ions and co-factors

52
Q

what enzymes do periplasmic proteins have

A

degradative

“Detoxifying”

53
Q

what are the examples of degradative enzymes - periplasm

A

proteases and nucleases

54
Q

what are the examples of detoxifying enzymes - periplasm

A

-lactamases which break-down penicillin

55
Q

what continues energy production in periplasm

A

cytochromes

56
Q

what do cytochromes do

A

required to keep electron-transport and therefore energy production continuing

57
Q

what is Mycobacterium tuberculosis like

A

unusual Gram +ve bacterium

58
Q

what is the layer of MB TB like

A

forms thick outer layers, including a special “mycomembrane”

mycolic acids

59
Q

effect of thick mycobacterium - mycomembrane

A

gives it resilience against innate immune system

60
Q

effect of mycolic acid

A

make a novel kind of outer membrane which helps resist damage from macrophages when the Mycobacteria are causing tuberculosis (TB)

61
Q

what is the capsule like

A

Loose slimy layer around outside of some bacteria

hydrophilic polymer

62
Q

what is capsule usually made of

A

sugar molecules such as fructose and glucose

63
Q

what can capsule prevent

A

pathogenic bacterium being enveloped and destroyed by phagocytes in host defence mechanisms in blood

64
Q

what may capsule allow

A

bacterium to attach to a surface, e.g. Streptococcus mutans which causes plaque on teeth

65
Q

what senses the capsule

A

host immune system

66
Q

how are capsules viewed - microscope

A

Capsules on microscope use Indian Ink Staining
Not all bacteria of one type/strain make them at any one time - a process called phase variation can invert the promoter (on/off) at a gene that controls their synthesis

67
Q

where is the S-layer found

A

in several different bacterial species

Usually external to all other layers an alternative to a capsule

68
Q

what is the S-layer like

A

rigid crystalline lattice composed of protein (or glycoprotein) subunits arranged in a regular array

69
Q

how are the protein subunits assembled in S-layer

A

Protein subunits have self-assembly properties and may form sheets several molecules thick

70
Q

what are S-layers resistant to

A

resistance to proteolytic enzymes and may protect against phage infection

71
Q

what is the S-layer function

A

protective

72
Q

Protruding structures from bacterial cell surface examples

A

flagella
fimbriae
related pili

73
Q

what do cell membranes and gram -ve bacterium have

A

Flagellar motor, rotor and drive shaft

74
Q

what are flagella like

A

Long
wavy
helical filaments
protrude from cell surface of may different bacteria

75
Q

what is the flagellar arrangement

A

polar or peritrichous

76
Q

how many flagellar are present in bacteria

A

variable in number depending on bacterial species

77
Q

what make up the flagella

A

several different proteins, main body of flagellum, filament, is a hollow cylinder made up of a helical array of protein subunits. Different proteins compose other parts of the flagellum

78
Q

how do bacteria swim

A

Flagella rotate at high speed from basal motor complexes in cytoplasmic membrane

79
Q

why do bacteria need to move

A

swim through aqueous environments e.g. gut contents in humans or in mouth

80
Q

what powers the flagellar movement

A

Rotation powered by ion-motive gradient across cytoplasmic membrane (usually proton gradient). Ions are thought to interact electrostatically with motor proteins to cause rotation, unknown mechanism

81
Q

is ATP needed in flagella rotation

A

Rotation does not require hydrolysis of ATP

82
Q

where do flagella filaments grow from

A

distal end
Self-assembly of external components of flagella occurs at the distal end of the growing flagellum, monomers being secreted from the cell and travelling up hollow centre of the flagellum

83
Q

what is flagellin

A

main propeller protein

84
Q

why are flagellin sequences varied

A

evade immune recognition

85
Q

why do flagella evoke immune response

A

No known homologues in eukaryotes so evoke an immune response

86
Q

what are flagella required for

A
  1. Required for many bacteria-higher organism interactions, such as host interaction reaching gut mucosa by swimming from lumen, but not essential for life
87
Q

what signals define flagella direction movement

A

Flagellar motor- rotation drives swimming and tactic signal CheY to FliM defines direction

88
Q

where do flagella swim to

A

Swimming = bacteria reach optimum environments for growth, or for pathogens to reach infection sites on hosts

89
Q

what is in the flagellum base

A

proteins concerned with export of flagellar components

90
Q

what does the type III exporter tip

A

integrates into human cell membrane, delivers effector proteins

91
Q

what are the fimbriae types

A

Type 1 or common pili

92
Q

what are fimbriae like

A

Straight
usually stationary
filaments protrude from surface of many bacteria

93
Q

how are fimbriae proteins arranged

A

protein molecules arranged in a helix to form the cylindrical shape

94
Q

how do fimbriae grow

A

New molecules are added at the base as new fimbriae grow

95
Q

why is the tip in fimbriae important

A

Function to allow attachment of bacteria to each other or to surfaces. Specialised tip proteins on fimbriae allow binding specificity

96
Q

what are the conjugative pili

A

sex or F pili (As some encoded by F plasmid)

97
Q

what are conjugative pili like

A

Straight
stationary (non-waving or rotating, but retractable)
filaments which protrude from bacteria surface which carry certain plasmids

98
Q

how many conjugative pili are there in each bacterial cell

A

one or two pili found per bacterial cell

99
Q

what is a conjugative pili composed of

A

Composed of a cylindrical helix of protein (pilin) molecules

100
Q

what does conjugative pili allow

A

allow attachment of 2 compatible bacteria for the transfer of genetic material

101
Q

what do sex pili allow

A

allow bacteria to conjugate and pass their DNA around - allows many different genes to be acquired including genes for surface structure variation

102
Q

what is conjugation

A

natural process, leads to antibiotic resistance in hospitals by gene transfer from soil bacteria to pathogens

103
Q

what happens if pili are recognised

A

If pili recognized and bound by antibodies they can’t extrude and retract so gene transfer can’t occur

104
Q

what do conjugative plasmids encode

A

pilus structure and transfer DNA

105
Q

Bacterial Conjugation using sex pili

A

Bacteria come together via attachment of the E.coli sex pilus coded for by the plasmid DNA in the E.coli
Pilus retracts and cytoplasms fuse for plasmid transfer

Infection and Immunity (29 decks)

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