If a mutation alters the identity of an amino acid in a protein, hydrogen bonds may be broken, or new ones formed. Whole webs of hydrogen bonds may shift a little, including those that pinion a redox centre into its correct position. It might well move by an ångström or so. The consequences of such tiny shifts are magnified by quantum tunnelling: an ångström this way or that could slow down electron transfer by an order of magnitude, or speed it by an equivalent factor. That’s one reason why mitochondrial mutations can be so catastrophic.
