Shape and motility of a model cell: A computational studyComputer simulations were performed to examine the effects of the main ͑backbone͒ and side ͑branch͒ chain size on the shape and dimensions of a polymacromonomer using the bond fluctuation model in which bond cutting is allowed. The polymacromonomer was treated as a self-avoiding chain having N bonds in the main chain and n bonds in the side chains which are attached to every main chain element. In the simulation N and n were varied up to 64. A power law relation, ͗S 2 ͘ m ϳN 2 m , was obtained for each value of n, where ͗S 2 ͘ m is the mean-square radius of gyration of the main chain. The exponent 2 m increased monotonically from 1.24Ϯ0.02 at nϭ1 to 1.95 Ϯ0.05 at nϭ64, indicating that the shape of the main chain gradually varied with increasing n, from a self-avoiding coil-like structure to an extended rod-like form. The mean-square radius of gyration of the side chain moiety, ͗S 2 ͘ s was independent both of N and also of the position of the branching point along the main chain for every value of n. A power law relation was also found between ͗S 2 ͘ s and n, with exponent 2 s ϭ1.20Ϯ0.01. This exponent is the same as that for a linear chain, while ͗S 2 ͘ s is about 1.2 times the value ͗S 2 ͘ of a linear chain with the same degree of polymerization.This strongly suggests that all side chains maintain a three-dimensional self-avoiding coil-like form, irrespective of the main chain, as it extends from a coil-like form to a rod-like form with increasing n.

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