ROLE OF CYTOARCHITECTURE IN CYTOPLASMIC TRANSPORT

Cytoplasm is a thick viscoelastic gel consisting of a highly concentra ted protein solution interspersed through a matrix of cytoskeletal fil aments ansi organellar structures. Diffusion of soluble low-molecular- weight molecules through cytoplasm is slowed by a factor of 5-10 relat ive to a dilute aqueous solution, reflecting increased solvent viscosi ty, molecular crowding, tortuosity imposed by cytoplasmic membranes an d organelles, and transient binding to immobile structures. Larger mol ecules are further slowed by cytoskeletal sieving. Messenger RNA and r ibosomes may be prevented from entering certain parts of cytoplasm due to their size and may follow preferential channels as they exit the n ucleus. Mechanisms also exist for energy-dependent transport of larger molecules and organelles. Copyright (C) 1996 Elsevier Science Inc.