The bacterial cell wall is very rigid and gives cells their shape while protecting them from osmotic lysis and toxic substances. It is the site of action for several antibiotics. Gram-positive cell walls are 20-80 nm thick with peptidoglycan as the major component, linked by peptide interbridges. They also contain teichoic acids connected to peptidoglycan or plasma membrane lipids. Peptidoglycan, also called murein, is a heteropolymer containing sugars, amino acids, and peptide cross-links that connect peptidoglycan chains and give the cell wall strength.

1. Bacterial cell wall
Presented by-SAUBHAGYA KIRNENDRA
SRI VENKATESWARA COLLEGE
NEW DELHI

2. Bacterial Cell Wall

3. Characteristics
• Very rigid
• Give the cell shape and protect from osmotic lysis
• The strength of the wall is mainly due to peptidoglycan
• It also protects from toxic substances
• Site of action of several antibiotics
• Christan Gram (1884) proved that there are two major groups
of prokaryotes based on the composition of the cell wall
• Some bacteria such as Mycoplasma lack cell wall

4. Gram Positive Cell Wall
• 20-80 nm thick peptidoglycan layer
• Peptidoglycan is the major component of GPB
• Successive units of peptidoglycan are linked via peptide interbridge
• GPB cell wall is also rich in Teichoic acids
• Teichoic acids are polymer of Glyerol or Ribitol joined by phosphate
group. Amino acids such as D alanine or sugars like glucose are
attached to glycerol and ribitol groups
• Teichoic acids are connected to peptidoglycan by covalent linkage
with 6- hydroxyl of NAM or to lipids of plasma membrane
(lipoteichoic acids)
• Teichoic acids are supposed to provide strength to the cell wall

5. Gram Positive Cell Wall

6. Gram Positive Cell Wall
• Staphylococcus and some other GPB have a layer of protein on the
surface of cell wall
• These proteins interact with the surrounding environment and are
non covalently attached to peptidoglycan or teichoic acids
• Some of the enzymes (proteins) involved in peptidoglycan synthesis
are also known to be covalently attached to the cell wall
• However, many proteins are covalently linked to the cell wall
• Covalently linked proteins are involved in adhesion of pathogens to
host, preventing opsonisation, blocking phagocytosis

7. Peptidoglycan
• Also known as Murein is an enormous heteropolymer
• The polymer contains two sugar derivatives, N-acetylglucosamine and
N- actelymuramic acid and several amino acids (D- glutamic acid, D-
alanine, meso-diaminopimelic acid and L-alanine)
• Out of these amino acids first three are not found in proteins hence,
they protect against the attack of peptidase
• The back bone of the polymer is composed of alternating NAG- NAM
residues
• The peptide chain of four alternating D and L amino acids is
connected to carboxy group of NAM by amino group of L- alanine

8. Peptidoglycan
• Chains of linked peptidoglycan subunits are joined by crosslinks
between the peptide
• The carboxyl group of terminal D-alanine is connected to the amino
group of DAP of subsequent unit
• Peptide interbridge is used in GPB to connect the adjacent chains of
peptidoglycan
• Peptide interbridge is made up of five units of glycine
• The cross linkage result in a sac like structure of peptidoglycan which
is dense, highly interconnected, elastic and stretchable

9. Peptidoglycan structure

10. Peptidoglycan structure