Is the peptidoglycan layer a single molecule?

No, the peptidoglycan layer is not a single molecule. It is a vast polymer made up of interlocking chains of identical peptidoglycan monomers. Each peptidoglycan monomer consists of alternating chains of two glucose derivatives - N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM). These long alternating chains are cross-linked to each other by a tetrapeptide extending off the NAM unit.