Prokaryotic Cell Wall
• Cell wall was first observed and named as
wall by Robert Hooke in 1665.
• In 1804, Karl Rudolphi and JHF Link proved
that bacterial cells have cell walls.
• It can be tough, flexible and rigid & provides
structure and shape and protects cell from
osmotic forces
• Assists some cells in attaching to other cells or
in eluding antimicrobial drugs
• Animal cells do not have cell wall; can target
cell wall of bacteria with antibiotics
Bacterial Cell Wall
• Most have cell wall composed of peptidoglycan; a few
lack a cell wall entirely
• Peptidoglycan composed of sugars, NAG, and NAM
• Chains of NAG and NAM attached to other chains by
tetrapeptide crossbridges
– Bridges may be covalently bonded to one another
– Bridges may be held together by short connecting
chains of amino acids
• Scientists describe two basic types of bacterial cell
walls: gram-positive and gram-negative
• Cell wall of Fungi: Chitin and Plant: Cellulose
Gram-Positive Cell Wall
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•
•
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Relatively thick layer of peptidoglycan
Peptido-glycan Polymer-amino acids + sugars
Unique to bacteria
Sugars; NAG & NAM
– N-acetylglucosamine
– N-acetymuramic acid
• D form of Amino acids used not L form
– Hard to break down D form
– Amino acids cross link NAG & NAM
• Contains unique polyalcohols called teichoic acids
– Some covalently linked to lipids, forming lipoteichoic acids
that anchor peptidoglycan to cell membrane
• Retains crystal violet dye in Gram staining appear
purple
• Acid-fast bacteria contain up to 60% mycolic acid; helps
cells survive desiccation
Peptidoglycan
N-acetylglucosamine (NAG) - N-acetylmuramic acid (NAM)
• Polymer of disaccharide
(NAG-NAM)n
• Linked by polypeptides
Teichoic acid – polymer of glycerol
or ribitol phosphate
• Generation of the net
negative charge of the cell - PMF
• Maintenance of the cell
shape, particularly in rodshaped organisms - rigidity
of the cell wall
• Participate in cell division,
by interacting with the
peptidoglycan biosynthesis
machinery
•Resistance to adverse
conditions such as high
temperatures and high salt
concentrations, as well as
to β-lactam antibiotics
Gram Positive Cell Wall
•Thick layer peptidoglycan
•Teichoic acid
• Lipoteichoic acid
Gram-Negative Cell Walls
• Have only a thin layer of peptidoglycan
• Bilayer membrane outside the
peptidoglycan contains phospholipids,
proteins, and lipopolysaccharide (LPS)
• May be impediment to the treatment of
disease
• Following Gram staining procedure, cells
appear pink
Gram-Negative cell wall
• The cell wall is relatively thin (10 nanometers) and is composed of:
1. A single/bi layer of peptidoglycan, no penta glycine bridge/less
cross linking
2. Outer membrane - part of the cell wall
Outer membrane composition is distinct from that of the cytoplasmic
membrane - unique component, lipopolysaccharide (LPS or endotoxin),
which is toxic to animals.
O polysaccharide part - antigen
Lipid A - endotoxin
Porins (proteins) form channels through
membrane
Protection from phagocytes,
complement, antibiotics.
3. Periplasm – area between the outer
membrane and the plasma membrane.
Lipopolysaccharide (LPS)
Lipid portion known as lipid A
• Dead cells release lipid A when cell wall
disintegrates
• May trigger fever, vasodilation,
inflammation, shock, and blood clotting
• Can be released when antimicrobial
drugs kill bacteria
Structure of Lipopolysaccharide
Structure of Lipid A
Repeat Units of O Antigen Side
Chain
Example: (Repeated up to 40 times)
Mannose
Abequose
Rhamnose
Galactose
 Heat stable O antigen is often used to serotype
• Outer Membrane
Gram Negative Cell wall
• LPS-lipopolysaccharide (Endotoxin)
• Porins
• Periplasm
Schematic representation of the envelop of Gram positive & negative bacteria
Beta-lactam Antibiotics
β-Lactams are a broad class of
antibiotics that all contain a βlactam ring in their molecular
structures.
Beta-lactam drugs include penicillin
derivatives (penams),
cephalosporins (cephems),
monobactams, and carbapenems.
These antibiotics work by inhibiting
cell wall synthesis in bacteria and
are the most widely used group of
antibiotics.
Penicillin needs to come directly
into contact with peptidoglycan to
cause cell wall damage. So what
type of cell wall do you think is
more vulnerable to damage by
penicillin?
1. Penicillin
2. Cephalosporin
Beta-lactam Antibiotic Resistance
Some bacteria have developed resistance to β-lactam antibiotics and
are able to synthesize an enzyme called β-lactamase, that
attacks the β-lactam ring, inactivating the antibiotic.
Penicillin
Broken
Penicillin
Schematic representation of the mycobacterial cell envelope
KEY WORDS
•Gram positive bacteria & gram negative bacteria
• Peptidoglycan (murein)
N-acetylglucosamine (NAG) and N-acetylmuramic acid
(NAM) linked via β-(1-4) linkage,tetrapeptide (Lalanine, D-glutamine, L-lysine, meso-diaminopimelic
acid (DPA), D-alanine),peptide interbridge
(Pentaglycine)
• Teichoic acid, wall teichoic acid (WTA), lipoteichoic
acid
• Lipopolysaccharide (LPS), O-antigen or Opolysaccharide, core polysaccharide, lipid A, endotoxin
• Chlamydiae, Tenericutes - sterols