Mitochondria are surrounded by a double-membrane system, consisting of inner and outer mitochondrial membranes separated by an intermembrane space (Figure 10.1). The inner membrane forms numerous folds (cristae), which extend into the interior (or matrix) of the organelle. read more
Because of this double-membraned organization, there are five distinct compartments within the mitochondrion. There is the outer mitochondrial membrane, the intermembrane space (the space between the outer and inner membranes), the inner mitochondrial membrane, the cristae space (formed by infoldings of the inner membrane), and the matrix (space within the inner membrane). read more
If we compare to a prokaryotic cell, which does not have a membrane-bound nucleus at all, we observe one major evolutionary benefit of a membrane-bound nucleus is that it allows for an additional level of regulating gene expression. read more
The original bacteria had a double membrane and that double membrane was an integral part of the energy producing pathway that became so important for the eukaryotic cell. It's simply not true that the double membranes of bacteria and chloroplasts were the result of endocytosis. read more