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Y2 Microbiology > Thee Bcaterial Cell Envelope > Flashcards

Thee Bcaterial Cell Envelope Flashcards

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Biology 101 flashcards
1
Q

Majority of bacterial envelopes consist of?

A
  1. Plasma Membrane (lipid bilayer)
  2. Peptidoglycan (Cell wall)
  3. Envelope proteins
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2
Q

Gram Pos VS Gram Neg - bacterial envelopes

A

Gram pos
-Thick peptidoglycan layer
-Single membrane
-Lipotechoic and Techoic acid polymers

Gram neg
-Thin peptidoglycan layer
-Inner membrane and outer membrane
-LPS (endotoxin) surface polymer

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3
Q

What are 2 types of bacterial envelopes?

A

Mycobacterial and wall less

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4
Q

What does Mycobacterial envelope consist of?

A

-Thin peptidoglycan layer
-Single membrane
-Mycolic acid layer (hydrophobic)
-Arabinogalactan links peptidoglycan and mycolic acids

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5
Q

What do Wall-less bacterial envelopes consist of?

A

-No peptidoglycan synthesis
-Must live in osmotically balanced environment

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6
Q

Who was the gram stain developed by and in what year?

A

Hans Christian Joachim Gram in 1880

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7
Q

What was the gram stain initially used to distinguish between?

A

Streptococcus pneumoniae (gram pos) and Klebsiella pneumomiae (gram neg)

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8
Q

What are the 4 additions used in the gram stain

A
  1. Crystal Violet
  2. Iodine
  3. 95% Ethyl Alcohol
  4. Safranin
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9
Q

What happens at the addition of crystal violet and iodine?

A

-Positively charged crystal violet binds to negatively charged molecules - techoic acids of Gram pos and LPS of gram neg
-All bacteria are stained purple
-Iodine complexes with crystal violet and acts as a ´trapper´

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10
Q

What happens after the addition of Ethyl Alcohol?

A

-Decolouriser reagent
-Solubilises membranes
-Gram neg outer membrane stripped away including LPS and associated crystal violet

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11
Q

What happens after the addition of Safranin?

A

-Acts as a counterstain
-Binds to peptidoglycan and associated polymers of both gram neg and gram pos bacteria
-CV coloration overpowers Safranin in gram pos

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12
Q

What colours are gram neg or gram pos bacteria after the gram stain?

A

Gram pos are blue to purple
Gram neg are red to pink

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13
Q

Why is Gram staining impossible in Mycobacteria?

A

Because of the hydrophobic mycolic acid layer

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14
Q

What is used instead of gram stain for Mycobacteria?

A

Ziehl-Nielsen Staining uses carbol-fushin (pink stain), phenol and heat to allow penetration of mycolic acid layer.
Carbol-fushin associates w neg charged components of cell envelope including mycolic acids

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15
Q

What are the functions of the cytoplasmic membrane?

A

-Permeability barrier
-Protection anchor
-Energy conservation - ATP and essential co-factor generation is dependent on membrane bound proteins

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16
Q

What are the 2 key regions of membrane lipids?

A

-Hydrophilic region
-Hydrophobic region

17
Q

What are examples of hydrophilic lipids?

A

-Glycerol
-Phosphate
-Ethanolamine

18
Q

What is an example of hydrophobic lipid in membrane?

A

Fatty acids

19
Q

Functions/Features of the cell wall (peptidoglycan)

A

-Forms mesh structure that gives strength to cell envelope
-contains plasma membrane
-captures high conc of soluble molecules by acting as a sponge
-able to contain osmotic pressure up to 208kPa
-acts as anchor for surface molecules e.g proteins and polymers
-Major target for antibiotics due to essential for survival of bacteria

20
Q

What is the difference between peptidoglycan structures between pos and neg bbacteria

A

Gram pos= THICK
Gram neg= THIN

21
Q

What are the repeating disaccharides that form the polysaccharide backbone in peptidoglycan?

A

NAM - N-Acetylmuramic acid
NAG - N-Acetylglucosamine
Joined by glycosidic bonds

22
Q

What is the name given to amino acids attached to NAM? and what gives the structural rigidity to the cell wall?

A

´Stem-peptide´
Crosslinking between adjacent polysaccharide strands

23
Q

What positions are bonded in stem peptide crosslinking in bacteria and archaea?

A

Position 3 to position 4 peptide bond

24
Q

What is the diff betwen the stenm peptide linkage in Gram Pos and Gram Neg bacteria?

A

Gram Neg - direct linkage between meso-diaminopimelic acid (DAP) to D-alanine

Gram Pos - indirect linkage between L-lysine and D-alanine using a pentaglycine bridge

25
Q

How can active transport be achieved?

A
  1. Simple transporters
    2.Group translocation (TAT and PES systems)
  2. ABC transporters
26
Q

How do Simple Transporters facilitate the transport of molecules and what are examples of these?

A

-Simple transporters use H+ ions to facilitate transport of molecules into and out of the cell

i) Antiporter - Sodium proton antiporter- Transported molecule moves in opposite direction to H+ to outside cytoplasm

ii) Symporter -Lac permease- Transported molecule moves in same direction as H+ into the cell

27
Q

Group translocation - Phosphotransferase system- PTS system

A

-Requires multiple enzymes
-Transported substances are chemically modified - phosphoralated or dephosphorylated
-E.g dephosphorylation of pyruvate required for entry into TCA cycle,

28
Q

What is the ABC transporter system and what are the 3 components it requires?

A

Large family of transporters with a wide target molecule range

  1. Sustrate binding protein (Periplasm/extracellular)
  2. Transmembrane transporter
  3. ATP - hydrolysing enzyme (cytoplasm)
29
Q

What is the bacterial membrane essential for?

A

Energy synthesis and conservation

30
Q

What are techoic acids?

A

Simple polymers of repeating sugar units which decorate Gram pos cells

31
Q

What are the 2 major types of techoic acids?

A
  1. Wall Techoic Acids (WTA) - Covalently linked to peptidoglycan
  2. Lipoteichoic acid - Attached to plasma membrane
32
Q

What are Lipoglcan molecules?

A

-Lipoglycans found as part of outer memebrane of Gram neg bacteria
-Negatively charged

33
Q

What do lipoglycans consist of?

A

-Lipid A - hydrophobic domain (exotoxin)
-Core oligosaccharide - hydrophyllic non-variable core oligosaccharide.
-O-antigen - Repeating hydrophilic distal polysaccharide

34
Q

What is the S layer?

A

-2-D Protein layer on outer membrane or peptidoglycan
-Anchored non-covalently through interactions with LPS in gram negs and wall techoic acid in gram pos

35
Q

What is the capsule?

A

-Gelatinous polysaccharide lavers which cover bacterial cells
-Hydrophilic
-During infection capsule polysaccharide inbibits phagocytosis

Y2 Microbiology (15 decks)

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