Question

How do organisms "control" the structures of the cell walls that they produce?

Answer 1

The structure of the cell wall is controlled various intrinsic factors like microbirils, protiens and extracellular molecules interacting with extrinsic factors like pressure, osmosis, availability of food soruce. This has been obeserved commonly in plants and also in some bacterias.

Changes in the cell shape resulting from changes in the cell's chemical environment may be clarified by changes in the plastic and elastic properties of the wall due to changes in the structure of the membrane. The cell wall has varied fuctions like maintaining the turgor pressure, control rate of growth, regulate diffusion, store carbohydrates in terms of seed walls, protects against harsh environment and pathogen attack. To support all these functions the cell wall shape and size does varies according the external stimuli. Cell expansion involves the synthesis of new material from the cell wall and regulated loosening of the wall to allow it to expand and increase area. The so-called expansin family of cell-wall-associated proteins are important components in this process. Expansions increase the wall extensibility, probably by breaking non-covalent bonds between wall polysaccharides and allowing them to move relative to each other. The cessation of growth that takes place during cell maturation is
generally irreversible and followed usually by a reduced extensibility of the wall, as calculated by different biophysical methods. Such improvements in the wall may be physical are carried out  by (1) reducing the loosening of walls,

(2) an increase in the cross-linking of the wall,

(3) a change in the wall composition, making a stiffer structure or less vulnerable to loosening of the wall.

The wall of plant cells is not simply a rigid and inert exoskeleton. The wall, besides serving as a mechanical retainer uses as an extracellular matrix that interacts with proteins on the cell surface, providing spatial and developmental data. It contains many enzymes, and smaller molecules which are biologically active and which can change the physical properties of the wall, rarely in seconds. These are facilated by two types of dynamic changes that can occur in mature cell walls: hydrolysis and oxidative cross-linking. Hemicelluloses and pectins can be altered and broken down by a number of enzymes naturally present in the cell wall. In diffuse-growing cells, wall structure determines the directionality of growth, particularly the orientation of the cellulose microfibrils, which in turn is determined by the orientation of microtubules in the cytoplasm. Upon exiting the meristem, typically plant cells elongate greatly. Cell enlargement is restricted by the ability of the cell wall to undergo polymer creep, which in turn is complexly regulated by the adhesion of wall polymers to each other and by the effect of pH on wall-loosening proteins such as expanses, glucanases, and other enzyms.