Question

Lesson 4

1. What type of molecule provides cross-link for the peptidoglycan polymer?

2. How is the peptidoglycan differs between gram positive and gram negative bacteria?

Answer 1

The bacterial cell wall is made of peptidoglycan or murein  - a polymer made up of f β-(1,4) linked sugars linked N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM). A pentapeptide chain ( peptide with 5 aminoacids, in E coli these amino acids are L alanine, D glutamic acid, meso diaminopimelic acid, and two D alanine  ) is attached to NAM. This pentapeptide can cross link with the pentapeptide of other NAM molecules there by cross linking peptidoglycan polymers in a 3D network.

Gram positive bacteria have thicker peptidoglycan layer ( made up of several layers of peptidoglycan, 20-80 nm thick) while gram negative bacterial cell wall thickness is about 7-8 nm only ( has a single layer of peptidoglycan). Gram positive bacteria has molecules called teichoic acids that run perpendicular to peptidoglycan layer. Gram negative bacteria has an outer membrane made of lipopolysaccharide surrounding their peptidoglycan layer.