肽聚糖，存在于真细菌中的革兰氏阳性菌和革兰氏阴性菌的细胞壁中。肽聚糖的骨架是由两种糖衍生物：N-乙酰葡糖胺（GlcNAc）和N-乙酰胞壁酸（MurNAc）交替相连而形成的多糖链，这些链相互交联形成肽聚糖（如图1）。从每个N-乙酰胞壁酸引出一条寡肽链，与相邻多糖链上的N-乙酰胞壁酸相连（如图2），使两条平行的糖链横向相连构成网络，这样构成了整个细菌表面的细胞壁（如图3）。

一个细菌只被一个胞壁质分子所包围。胞壁质也可以由几层由多肽相互交联的网络组成。尤其革兰氏阳性菌的胞壁质具有很多层。并不是所有细菌都具有相同的胞壁质，它们在肽链的氨基酸组成上会有不同，但糖链骨架总是一样的。革兰氏阳性菌的组成区别更大一些。

Peptidoglycan, also known as murein, is a polymer consisting of sugars and amino acids that forms a mesh-like layer outside the plasma membrane of most bacteria, forming the cell wall. The sugar component consists of alternating residues of β-(1,4) linked N-acetylglucosamine and N-acetylmuramic acid. Attached to the N-acetylmuramic acid is a peptide chain of three to five amino acids. The peptide chain can be cross-linked to the peptide chain of another strand forming the 3D mesh-like layer. Peptidoglycan serves a structural role in the bacterial cell wall, giving structural strength, as well as counteracting the osmotic pressure of the cytoplasm. A common misconception is that peptidoglycan gives the cell its shape; however, whereas peptidoglycan helps maintain the structural strength of the cell, it is actually the MreB protein that facilitates cell shape. Peptidoglycan is also involved in binary fission during bacterial cell reproduction.