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Microbiology > 7. Bacterial Cell Wall > Flashcards

7. Bacterial Cell Wall Flashcards

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Biology 101 flashcards
1
Q

What’s structure of bacterial cell

A

•Cellular envelope: cell wall,plasma membrane
•Extracellular polymeric substances
•Appendages:flagelli,pili/fimbriae
•Cytoplasmic compartment: cytoplasm, ribosomes, inclusion bodies, nucleoid

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2
Q

What’s bacterial cell wall

A

Bacterial cell wall-exoskeleton that provides shape and rigidity of the cell
It’s essential for cell viability (growth and division)
It provides protection against environmental stress(ex: mechanical, low pH, low osmolarity, bile salts)
-receptor site for phages

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3
Q

What’s bacterial cell wall responsible for

A

Antigenic variability of bacteria(serovars/serotypes)

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4
Q

Can bacterial cell wall be observed under microscope

A

Yes, with specific stainings

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5
Q

What taxonomic characteristic depend on cell wall

A

Morphology, gram reactivity, acid-fastness, antigenic specificity

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6
Q

What portion of cellular dry mass does cell wall take

A

10%-40%

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7
Q

What is classification of bacteria in 4 divisions?

A

4 devisions(phyla) is classification with phenic method:
1.Gracilicutes:Gram “-“ bacteria with thin cell wall, some of which obligate intercellular parasites
2.Firmicutes(Bacillota):Gram “+” bacteria with thick cell wall(ex: Bacilli, Clostridia)
3.Tenericutes(Mollicutes):bacteria with no rigid cell wall, order Mycoplasmatales
4. Mendosicutes:bacteria with “anomalous” wall, Archeobacteria

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8
Q

Compare Gram + and Gram- cell wall

A

Gram +: peptidoglycan*several layers), teichoic acids and proteins
Gram-: peptidoglycan(1/2layers), no teichoic acids+external membrane (made of lipopolysaccharides and porins)

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9
Q

What’s peptidoglycan

A

polymeric structure(polysaccharide) also called murein made of linear chains of consecutive units

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10
Q

What are amino sugars in peptidoglycan

A

•NAG- N-acetylglucosamine
•NAM- N-acylmuramic acid

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11
Q

How are 2 sugars connected

A

β(1-4) glycosidic bond

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12
Q

What’s attached to NAM

A

Peptide made out of 3-5 aa

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13
Q

How does peptidoglycan grow

A

While cell grows
Its grweth is finely tuned and coordinated with genomic DNA replication

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14
Q

What’s oligopeptide made out of

A

3-5 aa
1. L-Ala( Gly or L-Ser)
2. D-Glu(rarely Gly)
3. m-Dpm(meso,diaminopimelic acid) (Gram-); L-Lys(Gram +)
4. D-Ala:always
If there is 5th: D-Ala

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15
Q

Why are oligopeptides important in peptidoglycan

A

Because they links between the chains

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16
Q

How many peptidic bonds are normally formed by aa

A

2

17
Q

How many peptidic bonds(and why ) are formed by Lys and Dpm

A

Lysine has 2 aminic groups(-NH2) and 1 carboxylic(-COOH) forming 3 peptidic bonds
Dpm has 2 aminic groups and 2 carboxylic groups, forming 4 peptidic bonds

18
Q

How are bonds with side chains called

A

Cross-bridges

19
Q

What’s cross bridge in gram - and + bacteria

A

Gram-: CO-NH- (direct bond)
Gram +: (Gly)5-NH- (peptidic bridge 5Gly)

20
Q

What’s reaction for cross-links formation called

A

Trans-peptidation

21
Q

How are trans-peptidation reactions catalyzed

A

By transpeptides (mediating actual trans-peptidation) and carboxypeptidases( workind on D-Ala-D-Ala)
These anzymes are localized on cell membrane

22
Q

How are trans-peptidation enzymes categorized

A

As penicilin -binding proteins(PBP) =they are targeted by penicilin and other beta-lactam antibiotics

23
Q

How do bacteria escape binding of penicilin

A

Penicilin-resistant bacteria escape it by:
•synthesizing large amounts of PBPs
•modifying PBPs’ structure
•synthesizing additional version of PBPs

24
Q

What are teichoic acids

A

Teichoic acids-polymers of polivalent alcohols(glycerol or ribitol) esterified with phosphoric acid to which many different monosaccharides and/or aa can bind

25
Q

Where are they covalently bound

A

To peptidoglycan or cell membrane

26
Q

Hoe are teichoic acid called if they are bound to cell membrane

A

Lipoteichoic acids

27
Q

What covalent bond is between teichoic acids and peptidoglycan

A

Covalent bond eith OH- in posituon 6 of the NAM

28
Q

How are teichoic acids charged and what elements are they rich of

A

Negatively, rich in phoshporus (can be used as P source in case of deficit)

29
Q

In what bacteria are teichoic acids

A

Gram + and account for 60% of the cell wall

30
Q

What’s the role of teichoic acids

A

•stability:structural support to peptidoglycan
•surface antigents: characterize serotypes(hughly antigenic)
•provide net negative charge allowing passage of ions through the wall and binding of cations (ionic enviroment for membrane enzymes activities)
•control bacterial growth (regulation of autolysins activity)
•adhesion( also for infetuous agents,phages)

31
Q

How to Gram + bacteria tolerate high salt concentrations

A

Because off teichoic acids that provide negative charge

32
Q

What outer membrane of Gram - cell wall made out of

A

•Asymmetric lipidic double layer
•Braun’s lipo-proteins
•Channels(porins)
•Carrier proteins

33
Q

What’s asymmetric lipid bilayer made out of

A

Inner layer: phospholipids
Outer layer: lipo-polysaccharide(LDS)

34
Q

What’s asymmetric lipid bilayer made out of

A

Inner layer: phospholipids
Outer layer: lipo-polysaccharide(LDS)

35
Q

What are Braun’s lipo-proteins

A

Proteins that covalently tie the outer membrane to peptidoglycan. They bind m-diaminopimelic acid of peptidoglycan through C terminal lysine

36
Q

Why are channels and carriers proteins needed in Gram - bacteria

A

Because presence of lipids in the outer membrane doesn’t allow the passage of hydrophilic molecules

37
Q

What’s functuon of channels(porins)

A

They allow the passive diffusion of small molecules. They are trimeric proteins, for hydrophilic molecules smaller than 600-700Da (specific and aspecific porins)

38
Q

What’s function of carrier proteins

A

Active transport of larger molecules

Microbiology (20 decks)

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