Page 32 - MNU microbiology theoritical 2025

General Microbiology & Immunology (PM 401) Second level Semester 4 2024/2025

• The tetrapeptides can be directly cross-linked to one another, with the D-

alanine on one tetrapeptide binding to the L-lysine/ DPA on another

tetrapeptide.

• In many Gram-positive bacteria there is a cross-bridge of five amino acids such

as glycine (peptide interbridge) that serves to connect one tetrapeptide to

another.

• In either case the cross-linking serves to increase the strength of the overall

structure

Gram Positive Cell walls

1- Peptidoglycan

• Thick layer (as many as 30 layers) represents up to 90% of the cell wall, with

layer after layer forming around the cell membrane.

• The NAM tetrapeptides are typically cross-linked with a peptide interbridge.

• All of this combines together to create an incredibly strong cell wall.

2- Teichoic acid
• Teichoic acid is copolymers of glycerol

phosphate or ribitol phosphate and

carbohydrates which are embedded within

the peptidoglycan layers.

• lipoteichoic acids: Teichoic acids

covalently bound to cytoplasmic membrane

lipids.

General Microbiology & Immunology (PM 401) theoretical handbook Page 21