slide about bacterial cell wall,its structure and composition.

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