19. Mitochondria 01/09/12 21:25 cottingham Outer membrane – encloses mitochondria, contains protein channels. Inner membrane – folds into CRISTAE that encloses the MATRIX (the internal fluid of the mitochondria). KREBS CYCLE TAKES PLACE IN THE MATRIX! ELECTRON TRANSPORT CHAIN IN THE INNER MEMBRANE! Intermembrane Space – used in the ETC to hold hydrogen ions.