Chaperonins assist in the acquisition of native protein structure in the cell by 
providing a shielded environment for a folding polypeptide chain, generated by 
the interior surface of their cylindrical structure. The folding chain is 
isolated from the highly crowded cytoplasm, but at the same time confined within 
the chaperonin folding cage. Both confinement and macromolecular crowding can 
affect folding kinetics and yields, the modus operandi of chaperonins and their 
interaction with their protegés. Recent experimental data, as well as computer 
simulations, provide increasing evidence that the particular physico-chemical 
conditions prevailing in the cellular interior have to be taken into account 
when trying to unravel the processes of cellular protein folding.