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describe the structural subunits of a bacterial cell wall and how they are arranged


describe the structural subunits of a bacterial cell wall and how they are arranged

Step 1

The major component of the bacterial cell wall is peptidoglycan or murein. This rigid structure of peptidoglycan, specific only to prokaryotes, gives the cell shape and surrounds the cytoplasmic membrane.

Step 2

Murein is the ubiquitous component of bacterial cell walls. Murein is a unique type of peptidoglycan, a polymer of disaccharides (glycan) cross-linked by short chains of amino acids. Many types of peptidoglycan can exist. All bacterial peptidoglycans contain N-acetylmuramic acid, which is the definitive component of murein.

In the Gram-positive Bacteria, the cell wall consists of several layers of peptidoglycan. Running perpendicular to the peptidoglycan sheets is a group of molecules called teichoic acids which are unique to the Gram-positive cell wall. The cell wall is thick (15-80 nanometers), consisting of several layers of peptidoglycan. 

In the Gram-negative Bacteria, the cell wall is composed of a single layer of peptidoglycan surrounded by a membranous structure called the outer membrane. The outer membrane of Gram-negative bacteria invariably contains a unique component, lipopolysaccharide (LPS or endotoxin). In Gram-negative bacteria the outer membrane is usually thought of as part of the cell wall. The cell wall is relatively thin (10 nanometers) and is composed of a single layer of peptidoglycan surrounded by an outer membrane.

Step 3

In the peptidoglycan structure, the glycan backbone is made up of alternating molecules of N-acetylglucosamine (G) and N-acetylmuramic acid (M) connected by a beta 1,4-glycoside bond. The 3-carbon of N-acetylmuramic acid (M) is substituted with a lactyl ether group derived from pyruvate. The lactyl ether connects the glycan backbone to a peptide side chain that contains L-alanine, (L-ala), D-glutamate (D-glu), Diaminopimelic acid (DAP), and D-alanine (D-ala). MurNAc is unique to bacterial cell walls, as is D-glu, DAP and D-ala.

Strands of murein are assembled in the periplasm from about 10...

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