Bacteria dwell within a giant sack, a molecule called "the sacculus", which is made of a chemical called peptidoglycan. Like a novelty ballon, the sacculus is "inflated" from within by the innards of the bacterium, to attain a given shape. While the sacculus gives the bacterium it's shape, it also acts as a protective wall to prevent the bacterium from splitting open. The sacculus is constantly being broken down and re-made for various reasons by a series of proteins. Here, a stripped-down abstractification of the bare basics of this system are depicted. The sacculus itself is represented by the blue and green balls, connected by springs. The red helix inside the sacculus represents a protein (called MreB) which forms some form of supporting framework or track for another set or proteins, depicted as red balls, that do the maintenance work on the peptidoglycan.