Page 35 - MNU microbiology theoritical 2025

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

2- An outer membrane

It forms the outermost layer of the cell wall. It is composed of:
lipid bilayer Phospholipid bilayer similar in composition to the cell

membrane
lipopolysaccharides are anchored into the outer membrane and project from the cell
(LPS) (endotoxin) into the environment

LPS is made up of three different components:

1) O-antigen or O-polysaccharide represents the outermost

part, varies in length and composition, Serve as an antigenic

determinant

2) Core polysaccharide.

3) Lipid A: anchors the LPS into the outer membrane

- The endotoxic portion of the molecule.

- It causes fever and dilates blood vessels, so the blood

pressure drops.

- bacteria release endotoxin mainly when they are dying,

Porins Specialized channel-forming proteins that span the outer
membrane.

Lipoproteins are embedded in the outer membrane and covalently bonded
to the peptidoglycan.

This linkage between the two layers provides additional
structural strength

3- The periplasm contains enzymes for nutrient breakdown

General Microbiology & Immunology (PM 401) theoretical handbook Page 24