We describe a detailed study of the conformational properties of a very long polymer chain in the presence of small colloidal particles. The polymer chain is modeled by a random self-avoiding walk (SAW) on the cubic lattice. The properties of interest include the conformational entropy, segment distributions in the coil, and dimensions of the coiled chain attached to a particle. The conformational entropy of a coil perturbed by a nonadsorbing particle and by a particle attached to the chain end is calculated. The influence of the particle size on the minimum adsorption energy per surface unit of the particle, needed to outweigh the conformational entropy effect, is examined. The conformations of the free coil and the coil distorted by the irreversible adsorption of a particle are studied, On the basis of the results obtained, the possible structures of the particle-plus-polymer aggregates are discussed.