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Fundamentals of Microbiology (Y2,S1) > Bacterial Cell Envelope > Flashcards

Bacterial Cell Envelope Flashcards

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1
Q

What are bacterial envelopes

A

Multilayered protective structures which provides protection against hostile external environment

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2
Q

What do the majority of bacterial envelopes consist of (3)

A
  1. Plasma membrane (lipid bilayer)
  2. Peptidoglycan (cell wall)
  3. Envelope proteins
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3
Q

Components of the bacterial cell envelope are targets for what

A

Antibiotics

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4
Q

Features of gram pos bacterial envelope

A
  • Thick peptidoglycan layer -> increased turgor pressure
  • Single membrane
  • Lipotechnoic & Technoic acid polymers
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5
Q

Features of gram neg bacterial envelope

A
  • Thin peptidoglycan layer
  • Inner membrane & outer membrane
  • Lipopolysaccharide (endotoxin) surface polymer
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6
Q

Features of mycobacterial bacterial envelope

A
  • Thin peptidoglycan layer
  • Single membrane
  • Mycolic acid layer (hydrophobic)
  • Arabinogalactan links mycolic acids and peptidoglycan
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7
Q

Features of wall-less bacterial envelope

A
  • No peptidoglycan synthesis
  • Must live in osmotically balanced environment
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8
Q

When & by who was the Gram Stain developed

A

In the 1880s by Hans Christian Joachim Gram

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9
Q

Function of Crystal Violet during gram stain

A
  • Pos charged
  • Binds to petidoglycan & neg charged polymers -> Teichoic acids & LPS
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10
Q

Function of Iodine during gram stain

A
  • Complexes w crystal violet
  • “Trapper” reagent -> prevents crystal violet being washed away in further steps
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11
Q

Function of 95% Ethyl Alcohol during gram stain

A
  • Decolouriser reagent
  • Removes any dyes from lipid membrane
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12
Q

Function of Safranin during gram stain

A
  • Counterstain
  • Binds to peptidoglycan & associated polymers to give pink colour
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13
Q

Gram Pos gram stain resulting colour

A

Purple

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14
Q

Gram neg gram stain resulting colour

A

Pink

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15
Q

What feature of Mycobacteria makes gram staining impossible

A

The hydrophobic mycolic acid layer

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16
Q

3 functions of the plasma membrane

A
  1. Permeability barrier - prevents leakage, gateway fro transport of nutrients
  2. Protein anchor - site of proteins that participate in transport, chemotaxis
  3. Energy conservation - site of generation & dissipation of proton motive force
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17
Q

What is the plasma membrane completely impermeable for

A

Ions
They require transport proteins

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18
Q

Components of the hydrophilic region of the phospholipid bilayer of the plasma membrane

A
  • Glycerol
  • Phosphate
  • Ethanolamine
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19
Q

What are the components of the hydrophobic region of the phosphlipid layer

A

Fatty acids

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20
Q

Which have the more branched fatty acids chain; bacterial lipids or archaeal lipids

A

Archaeel lipids have more branched chains of fatty acids -> can be more fluid

21
Q

What does peptidoglycan consist of

A
  1. Amino acids (peptido)
  2. Repeating units of carbohydrates (glycan)
22
Q

Cell wall functions (6)

A
  1. Structural strength to cell envelope
  2. Contains the plasma membrane
  3. Captures high concentrations of soluble molecules (nutrients etc) by acting like a sponge
  4. Contains osmotic pressure up to 208kPa
  5. Anchor for surface molecules - proteins & polymers
  6. Target for antibiotics
23
Q

What kind of peptidoglycan do gram pos bacteria have

A

THICK

24
Q

What kind of peptidoglycan do gram neg bacteria have

A

thin

25
Q

What does petidoglycan consist of

A
  • A repeating disaccharide forming a polysaccharide backbone
26
Q

What does NAM stand for

A

N-Acetylmuramic acid

27
Q

What does NAG stand for

A

N-Acetlyglucosamine

28
Q

What gives structural strength to peptidoglycan layers

A

Crosslinking of amino acids on adjacent polysaccharide strands

29
Q

What are AAs attached to NAM called

A

The stem peptide

30
Q

What position bond is stem peptide crosslinking in bacteria & archaea

A

Position 3 to position 4 peptide bond

31
Q

What is the major molecular difference between Gram pos and neg peptidoglycan (GRAM NEG)

A
  • Position 3 on the stem peptide
  • Gram neg stem peptide linkage is a direct linkage between meso-diaminopimelic acid (DAP) to D-alanine
32
Q

What is the major molecular difference between Gram pos and neg peptidoglycan (GRAM POS)

A
  • Position 3 on stem peptide
  • Gram pos stem peptide linkage is indirect between L-lysine and D-alanine, using a pentaglycine bridge
33
Q

Osmosis

A

The diffusion of water across a membrane

34
Q

Diffusion

A

The movement of particles from an area of high conc to an area of low conc

35
Q

Active transport

A

Movement of particles against a concentration gradient

36
Q

What do simple transporters use to facilitate transport of molecules in & out of the cell

A

They use H+ ions

37
Q

How does an ANTIPORTER work

A

Transported molecule moves in the opposite direction to H+ to outside the cytoplasm

38
Q

How does a SYMPORTER work

A

Transported molecule moves in the same direction as the H+ ion, into the cell

39
Q

The phosphotransferase system (PTS system) is an exzmple of what kind of transport

A

Group translocation

40
Q

What happens in the phosphotransferase system

A
  • Requires multiple enzymes
  • Transported substances are chemically modified (glucose is phosphorylated, pyruvate is dephosphorylated)
41
Q

The 3 components the ABC transporter system needs

A
  1. Substrate binding protein (in periplasm/extracellular)
  2. Transmembrane transporter
  3. ATP hydrolysing enzyme (in cytoplasm)
42
Q

What are teichoic acids

A

Simple polymers of repeating sugar units which decorate gram pos cells

43
Q

What are the 2 types of teichoic acid and where are they found

A
  1. Wall teichoic acid - covalently linked to peptidoglycan
  2. Lipteichoic acid - attached to plasma membrane
44
Q

What do the lipopolysaccharides on gram neg outer membrane consist of

A
  1. Lipid A: Hydrophobic domain. Also known as an endotoxin!?
  2. Core Oligosaccharide: Hydrophilic non variable (same repeating sugars) core oligosaccharide
  3. O-antigen: repeating hydrophilic distal polysaccharide
45
Q

What is the S layer

A
  • Part of the envelope
  • Protein layer on outer membrane or peptidoglycan
46
Q

WHat is the S layer anchored to and with what bonds

A

Anchored non covalently through interactions with LPS in gram negs and wall teichoic acids in gram pos

47
Q

What is the capsule

A

They are gelatinous polysaccharide layers which cover bacterial cells

48
Q

FUnctions of capsule

A
  1. Prevents bacteria cells from desiccating in environment
  2. Keeps bacteria hydrated
  3. Inhibits phagocytosis during infection

Fundamentals of Microbiology (Y2,S1) (9 decks)

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