principles used by the cell are completely different to those used by architect
and available materials are all different; but the main difference is in the concept
. That is to say, there is no preconceived
model for life, just whatever will work
Life exists on an incredible range of scales, from nanometer building blocks to meter structures. To put this in another context, (nm : m :: m : earth->sun), so the human body spans a range equivalent to the solar system. This allows organisms to use a symphony of forces and timescales (again ns : s :: s : age of earth). A typical protein is around 5-10 nm wide, while a cell can be µmeters wide and capillaries are milimeters. Yet there are bacteria that only use the lower end of the scale, and viruses which are barely visible under conventional microscopes.
At the smallest, virus and protein scale, structures can be reversibly assembled and altered to order. Changes to the conditions of the environment affect the speed and stability of formation. This is not something that happens on the macroscale of buildings. Bridges do not fall apart in the rain, only to remake themselves when the sun comes out.
More importantly, there is no central designer directing the construction. Although DNA codes for the components, it makes little contribution to placing them itself. If a structure forms that is stable and can serve a useful purpose, it is maintained. Energetically expensive processes that burden the system tend to be removed.