Final answer:
Porin proteins form large channels that allow the passage of ions and small molecules and are found in the outer membrane of bacteria, but they are not involved in the transport of large proteins.
Step-by-step explanation:
Porin proteins are integral membrane proteins that facilitate the transport of molecules across a cell membrane. In discussing which statement about protein proteins is not true, we must consider the characteristics and functions of these channel proteins in biological membranes. Porin proteins indeed form large, barrel-like channels within the membrane, contrary to being small in size. They are designed to allow the passage of ions and small molecules, utilizing a hydrophilic channel that avoids the nonpolar central layer of the membrane. This is essential for polar compounds that cannot easily cross the hydrophobic membrane layers on their own. Regarding their location, porins are commonly found in the outer membrane of bacteria, serving as a point of selective entry and exit.
However, porins are not involved in the transport of large proteins; they are specific to ions and small polar molecules. Larger proteins require different mechanisms for transport across the cell membrane, such as active transport, which can involve carrier proteins or other complex translocation processes. In summary, the statement that porins are involved in the transport of large proteins is not true, making it the correct answer to the question regarding false statements about these channels.