7. Bacterial Cell Wall Flashcards
What’s structure of bacterial cell
•Cellular envelope: cell wall,plasma membrane
•Extracellular polymeric substances
•Appendages:flagelli,pili/fimbriae
•Cytoplasmic compartment: cytoplasm, ribosomes, inclusion bodies, nucleoid
What’s bacterial cell wall
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
What’s bacterial cell wall responsible for
Antigenic variability of bacteria(serovars/serotypes)
Can bacterial cell wall be observed under microscope
Yes, with specific stainings
What taxonomic characteristic depend on cell wall
Morphology, gram reactivity, acid-fastness, antigenic specificity
What portion of cellular dry mass does cell wall take
10%-40%
What is classification of bacteria in 4 divisions?
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
Compare Gram + and Gram- cell wall
Gram +: peptidoglycan*several layers), teichoic acids and proteins
Gram-: peptidoglycan(1/2layers), no teichoic acids+external membrane (made of lipopolysaccharides and porins)
What’s peptidoglycan
polymeric structure(polysaccharide) also called murein made of linear chains of consecutive units
What are amino sugars in peptidoglycan
•NAG- N-acetylglucosamine
•NAM- N-acylmuramic acid
How are 2 sugars connected
β(1-4) glycosidic bond
What’s attached to NAM
Peptide made out of 3-5 aa
How does peptidoglycan grow
While cell grows
Its grweth is finely tuned and coordinated with genomic DNA replication
What’s oligopeptide made out of
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
Why are oligopeptides important in peptidoglycan
Because they links between the chains
How many peptidic bonds are normally formed by aa
2
How many peptidic bonds(and why ) are formed by Lys and Dpm
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
How are bonds with side chains called
Cross-bridges
What’s cross bridge in gram - and + bacteria
Gram-: CO-NH- (direct bond)
Gram +: (Gly)5-NH- (peptidic bridge 5Gly)
What’s reaction for cross-links formation called
Trans-peptidation
How are trans-peptidation reactions catalyzed
By transpeptides (mediating actual trans-peptidation) and carboxypeptidases( workind on D-Ala-D-Ala)
These anzymes are localized on cell membrane
How are trans-peptidation enzymes categorized
As penicilin -binding proteins(PBP) =they are targeted by penicilin and other beta-lactam antibiotics
How do bacteria escape binding of penicilin
Penicilin-resistant bacteria escape it by:
•synthesizing large amounts of PBPs
•modifying PBPs’ structure
•synthesizing additional version of PBPs
What are teichoic acids
Teichoic acids-polymers of polivalent alcohols(glycerol or ribitol) esterified with phosphoric acid to which many different monosaccharides and/or aa can bind