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The channel has a large diameter of 0.8x1.1nm, and is non-selective for small ions. However, it has an upper exclusion size limit corresponding to molecular weights of about 600 Dalton of permeants. Because most metabolites have molecular weights lower than 600 Da and have been shown to pass through porin channels, porins are called general diffusion pores.
An ion is an electrically charged atom or group of atoms. It is a part of an atom, or part of a group of atoms (molecule). It is  charged  so it will move near electricity. This is because atoms are made of three smaller parts (1) neutrons (with no charge), and equal numbers of (2) charged protons and (3) oppositely-charged electrons. An ion has unequal numbers of protons and electrons. Making an ion from an atom or molecule is called ionization. The charge on a proton is measured as +1 (positively charged), and the charge on an electron is measured as -1 (negatively charged).