We study the configurational and dynamic properties of a long polymer chain during the process of penetration of the chain through the thin and porous membrane. The mobility of a polymer in this state depends strongly on the topological restrictions imposed by the membrane. The largest mobility have configurations in which the polymer chain crosses the membrane only once and diffuses through a single pore from one side of the membrane to the other. This configuration may have small statistical weight compared to other configurations with low mobility in which the polymer chain crosses the membrane many times. The relative weight of these configurations depends also on the chemical potential of the membrane. We find the configurations which give the main contribution to the transport and calculate the overall permeability of the membrane for Zimm and Rouse mechanisms of polymer dynamics