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Physiology of Microbes > Bacterial cell walls L6 > Flashcards

Bacterial cell walls L6 Flashcards

1
Q

what are the membrane bound cellular compartments

A

there is not any

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2
Q

where are the nucleic acids

A

free in cytoplasm

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3
Q

what is a nucleiod

A

DNA organised into structure associated with proteins

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4
Q

what surrounds the cytoplasm

A

rigid cell wall

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5
Q

what is the basic ‘building block’

A

peptidoglycan – murein (structure of amino acid, but not used in protein synthesis, used to build cell wall structure)

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6
Q

what is peptidoglycan (murein) made of

A

repeating dimers of two sugars

  1. N-acetylglucosamine (NAG)
  2. N-acetylmuramic acid (NAM)
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7
Q

where are the dimers of peptidoglycan assembled

A

cytoplasm

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8
Q

what is attached to the NAM residues

A

side chains of peptides

  • added to dimers before export
  • some amino acids in peptides are bacteria-specific – Mesodiaminopimelic acid
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9
Q

what bond joins the two sugars in murein

A

beta 1,4-glycosidic bond

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10
Q

what is the beta 1,4-glycosidic bond structure like

A

very flat –leads to making long linear chains

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11
Q

what is the beta 1,4-glycosidic bond sensitive to

A

lysozoyme

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12
Q

what is the first thing that acts against bacteria

A

lysozoyme

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13
Q

what form do enzymes not recognise

A

d forms

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14
Q

what form do enzymes recongise

A

L forms

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15
Q

why aren’t d forms used in our systems

A

quite toxic

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16
Q

what is peptidoglycan

A

long linear chains of repeating sugars

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17
Q

what are crosslinks

A

peptide bonds join two chains give overall rigidity of structure

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18
Q

how does the structure grow if it is a big cage like structure

A

need to grow from within structure, NOT adding onto ends – add into middle

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19
Q

what is the function of autolysin

A

create controlled cuts in peptidogylcan chains, insertion of disaccharide units

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20
Q

where does growth occur in the bacterial wall

A

growing points have controlled activity of autolysin, happen at very defined places

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21
Q

what is cell elongation

A

add in new dimers, dimers made in cytoplasm with peptide on, transported out, added on where cell wall cut

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22
Q

what are bactoprenols

A

specific transport molecules, ability to exist in cytoplasm, insert spontaneously into membrane

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23
Q

what is the function of bactoprenols

A

all flip, what was on inside on outside

new molecules can be flipped out and introduced into growth of new peptidoglycan

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24
Q

what is attached to bactoprenols and what do they cause

A

two phosphate groups attached to them – pick up two dimer molecules transported into membrane

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25
Q

what causes transpeptidation

A

penicillin binding protein

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26
Q

what does transpeptidation cause

A

allow chemical attack between reactive NH2 group and C-N bond so forms one peptide all the way across linking the two chains

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27
Q

what does penicillin do to the cell

A

weakens cell wall structure and leads to cell lysis

prevents transpeptidation

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28
Q

what do antibiotics do

A

stop cross links being formed, have long chains of sugar, but not turned into 3D mesh so cells weaker and eventually die

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29
Q

what colour are gram positive bacteria after purple dye added and washed with alcohol

A

retain crystal violet/iodine complex (purple) dye stays after washing

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30
Q

what colour are gram negative bacteria after purple dye added and washed with alcohol

A

Stain removed by alcohol from cell wall of Gram-negative bacteria
Counterstain (fuchsin) used to colour cells so they are visible
Gram-negative, colourless cells as not bound to cell – if coloured with fuchsin stay pink

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31
Q

what is a gram positive cell wall made of

A
  • 2D cross-linking of chains creates 3D sheets of PG in a rigid matrix
  • Glycine interbridges allow more flexible cross linking
  • Forms one giant scaffold-like molecule
  • Termed the murein sac or sacculus
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32
Q

how does peptidoglycan chains extend

A

can put in repeating glycine units, so get glycine inter-bridges so the chains can extend in more directions – can go between layers and between chains, can build
peptidoglycan in in 3D sheet

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33
Q

why do gram positive bacteria remain purple

A

dye trapped in peptidoglycan structure as complex is made, too big so can’t get out again

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34
Q

what is the second major component of gram positive cell wall

A

teichoic acid - up to 50%

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35
Q

what are the polymers of gram positive bacteria made of, what are they made into

A

glycerol phosphate or ribitol phosphate – these are then linked into long chains

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36
Q

what is the length and the types of side chain groups

A

varies depending on species

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37
Q

how can our body tell different gram positive bacteria apart

A

varied side chains
scanning these molecules, if they have same pathogen with recognised pattern of sugars antibodies have seen before, will active immune system to deal with pathogen

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38
Q

what are some teichoic acids linked to and what bond

A

covalently linked to N-acetylmuramic acid

some are attached to glycolipid in the underlying cell to form lipoteichoic acid

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39
Q

what covers the gram positive bacteria

A

smooth carbohydrate outer layer

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40
Q

what is the role of lipotechoic acid

A

anchoring PG layer to the cell-lipid bit anchored down in membrane, structural role – connects membrane and cell wall together

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41
Q

which bacteria have teichoic acids

A

gram positive bacteria

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42
Q

what is a form of a major antigenic determinants of cell surface

A

teichoic acid

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43
Q

what holds the bacterial cell wall together

A

lipoteichoic acids that are anchored in the membrane will be cross linked to peptidoglycan

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44
Q

what is the pseudoperiplasm and its function

A

gel like matrix

similar function to periplasm – transport enzyme function all occurs at this interface

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45
Q

where are the cross links in gram negative cell wall

A

only occurs in one plane

46
Q

what is the gram negative bacteria cell wall like

A

thin layer of peptidoglycan around cell

47
Q

what do the gram positive and negative bacteria have in common

A

peptidoglycan, little chemical resemblance between two bacterial structures

48
Q

where is the peptidoglycan in gram negative bacteria

A

thin sheet between two membranes

49
Q

where and what is the periplasm or periplasmic space

A

space between the two membranes

50
Q

what is the gel made of that fills the periplasm

A
  • proteins (hydrolytic enzymes, sensors, transporters, antibiotic resistance proteins)
  • small metabolites (enzymes broken things down into these)
  • oligosaccharides small sugars (create osmotic pressure buffer creates strength in cell wall)
51
Q

is peptidoglycan strong

A

not that strong

52
Q

what gives the bacterial cell wall strength

A

periplasm

53
Q

how can the immune system can tell different bacteria apart

A

carbohydrates extends to outside, is the variable region

54
Q

how does something enter a gram negative bacteria

A

has to go across outer membrane then inner membrane
porins – sit in outer membrane and allow exchange of molecules, they’re hollow, so lots of small molecules freely diffuse

55
Q

what is the structure of the gram negative bacteria

A
  1. Inner leaflet consists of ordinary phospholipids

2. Outer leaflet consists of a bacteria-specific molecule called lipopolysaccharide (LPS)

56
Q

what covers the gram negative bacteria

A

lipid rough outer surface

57
Q

what is LPS like to humans and animals

A

highly toxic to man and animals

  • endotoxin (= part of cell)
  • induces fever and shock even in minute amounts (endotoxic shock)
58
Q

if you have wrong antibiotics

A

receive second toxic shock if receive wrong

59
Q

what is an endotoxin

A

that forms part of the cell naturally that’s toxic to us if were exposed to it

60
Q

how does the gram negative bacteria recognise infection

A

immune system targets bacteria using those outer molecules and starts to break down cell wall structure, in doing so releases LPS can cause endotoxic shock (not infection is poisoning)

61
Q

what does LPS consist of

A
  1. Lipid A
  2. Core polysaccharide
  3. O-antigen (outer part
62
Q

what are other cell wall structures

A

acid-fast e.g. mycobacterium tuberculosis

63
Q

gram positive organism structure

A

lipid bilayer cell membrane covered by single porous peptidoglycan layer

64
Q

gram negative organism structure

A

surrounded by two membranes

outer membrane functions as a permeability barrier

65
Q

mycobacteria structure

A

thick mycolate-rich outer covering act as an exceptionally efficient barrier

66
Q

how are acid fast bacteria identified by

A

staining characteristics

e.g. they do not destain with acid and alcohol once stained with arylmethane dyes

67
Q

what acid do acid fast bacteria cell walls have

A
  • long chain, branched fatty acids
  • mycolic acids and short chain fatty acids form a pseudo outer membrane, result in unusual staining characteristics of cells
68
Q

what happens to gram positive, negative and acid fast bacteria in dye + washed

A

Gram-positive and Gram-negative de-colourise when washed with acid and alcohol, but acid-fast bacteria will stay stained
Dye fast – dye stuck to surface, will not come off

69
Q

what is acid fast bacteria cell wall like

A

waxy, hydrophobic and high lipid content
responsible for hydrophobicity of these cells
up to 60% of dry weight of organisms may be mycolic acids (thick layer)

70
Q

what is acid fast bacteria cell wall linked to and by what

A

linked to PG by arabinogalactan

71
Q

how is mycobacteria distinguished

A

type of mycolic acid

72
Q

what properties does the acid fast bacteria have, what may this cause

A

adjuvant

may be responsible for development of delayed type hypersensitivity

73
Q

how is the general immune system stimulated

A

adjuvant property, when infected get DTH, as presence of these molecules now making the immune system hyperalert to any other molecules its faced with

74
Q

how are mycolic acid and peptidoglycan linked

A

arabinogalactan

75
Q

how is the cell shape determined

A

by cell wall

76
Q

what is the bacteria interior like

A

very fluid interior

77
Q

what is the individual shape of cell outlined by

A

peptidoglycan, which has been laid down in particular way

78
Q

how is peptidoglycan laid down

A

in spirochete bacteria laid down to get cork screw shape, nucleic acid in cell labelled up with fluoroscent dye, if anything yellow is a spirochete

79
Q

what happens if bacteria are gently treated with lysozymes

A

strip outer cell wall, need to do this in osmotically balanced buffer NO turgor pressure
can see as time go on sphereoplasts form, is spirochete but DNA is converted from spiral shapes just into these spheres

80
Q

what are the other factors involved in cell shape

A

penicillin binding proteins in cell wall regulate pattern of PG biosynthesis
Other key shape determining protein = MreB

81
Q

what is the function of the penicillin binding proteins in cell wall

A
  • involved in controlling pattern of interbridges

- expression of PBPs regulated by morphogene (BolA)

82
Q

what is the function of MreB

A
  • forms actin-like cytoskeleton in some bacteria cells

- forms filaments, laid down in spiral-shaped bands around inside of cell under cytoplasmic membrane

83
Q

what happens in the cell division of FtsZ

A

FtsZ accumulates
Ring smaller as forms boa constrictor – pinches off so BPBs move inwards - septum grows inwards
after cell division loose FtsZ ring
divide in different planes
FtsZ ring always appears in same plane – controlled event so get chains

84
Q

what is the crescentin function

A

forms a track along cell – prevents as much peptidoglycan being put at bottom then to the top = cresent

85
Q

what happens if remove the cell wall from prokaryotes

A

most prokaryotes cannot survive without a cell wall

86
Q

how are spheroplasts formed

A

lysozyme treatment in osmotically balanced buffer

87
Q

where are mycoplasmas

A

naturally occurring cell-wall free bacteria

many pathogenic, living inside eukaryotic cells in osmotically-controlled environment

88
Q

what are the mycoplasmas membranes like

A

have tougher membranes to resist osmotic shock

89
Q

what cell wall do mycoplasmas have

A

really regulated so don’t need cell wall

90
Q

how do mycoplasmas gain structural integrity

A

accumulating molecules from their host cells

91
Q

why could mycoplasmas have lost their ability to synthesise cell wall

A

due to long association with hosts

= Obligate pathogens, needs to be inside host to replicate

92
Q

how much of the mycoplasma membrane is proteins

A

approximately 2/3 of membrane consists of proteins- strength

- all lipoproteins anchored to membrane

93
Q

what are the proteins in mycoplasma wall function

A

> majority have a structural role

> others have enzymatic activity, e.g. transport

94
Q

what do lipids consist of

A

phospholipids, glycolipids and neutral lipids

95
Q

what are the lipids like in prokaryotes

A

unique among prokaryotes in having a requirement for cholesterol in their membranes

96
Q

how does the mycoplasma make lipids

A

totally incapable of synthesizing own lipids, use the hosts

97
Q

what are archaea cell walls made of

A

pseudopeptidoglycan

  • repeating units of NAG & N-acetyl talosaminuronic acid
  • has β(1,3)
  • contains L-amino acids rather than D-aa seen in eubacteria
98
Q

what is the β(1,3) linkage for in the archaea cell wall

A

so is resistant to lysozyme

99
Q

what do some archaea lack

A

PG or pPG (pseudopepdidoglycan)

100
Q

what provides the cell wall with structure and strength

A

glycoprotein or protein

101
Q

what is the most common wall type among archaea

A

S-layer or paracrystalline surface layer

  • proteins arranged in a in regular array on cell surface
  • generally have hexagonal symmetry
102
Q

where are S-layers found

A

additional layers on some Eubacteria

archaea

103
Q

what type of bacteria is caulobacter crescentus

A

gram-negative

104
Q

what contains S-layer protein (RsaA)

A

Caulobacter crescentus

archaea

105
Q

what is on the Caulobacter crescentus cell surface

A

S-layer proteins exported on to cell surface in large quantities

106
Q

what happens if remove S-layer from bacteria

A

Exploited this as these bacteria can live without this layer

107
Q

how do bacteria make outer layer

A

bacteria have to produce a lot of protein and transport out – ABC transporter specifically recognizes RsaA protein pick it up and transport assemble into S layer

108
Q

what is LPS

A

major surface antigenic determinant

109
Q

what is lipid A

A

phospholipid containing glucosamine instead of glycerol. Toxic component of LPS

110
Q

what is the core polysaccharide

A

contains some unusual sugar residues but a fairly constant structure

111
Q

what is the outer part antigen

A

polysaccharide side chains with variable composition, forms major antigenic determinant

Physiology of Microbes (21 decks)

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