Fig. 5.

The PG cell wall grows by the addition of activated PG subunits to an existing cell wall under tension. Here the reaction depicts an existing network with area A, which can increase area by a small amount, dA. During the addition of PG, energy stored in the activated MurNAc and GlcNAc units drives the reaction. The assembly process is mediated by enzymes. One possibility is that since transpeptidases as well as hydrolyases are involved, the assembly reaction is reversible. Mechanical tension in the network shifts the reaction equilibrium and changes the net flux of materials to the right, thus affecting the size and shape of the cell.