The main function of mitochondria is

The ETC is localised in the mitochondria. The outer membrane of mitochondria is permeable to most of the small molecules. There is an intermediate space which presents no barrier to passage of intermediates. The inner membrane shows a highly selective permeability. It has transpo systems only for specific substances such as ATP, ADP, pyruvate, succinate, a-ketoglutarate, malate and citrate etc (Refer Fig. 10.1). The enzymes of the electron transpo chain are embedded in the inner membrane in association with the enzymes of oxidative phosphorylation. Extramitochondrial system: This is a radically different and highly active system responsible for de novo synthesis of palmitic acid from 2-carbon unit acetyl-CoA.Ref: MN Chatterjea Textbook of Medical Biochemistry, 8th edition, page no: 138 & 414