Mitochondria membrane protein assembly

Each mitochondrion (plural mitochondria) is bounded by two membranes (Figure 2.24a). The smooth outer membrane is relatively porous, because it is permeable to most molecules with masses less than 10,000 D. The inner membrane, which is impermeable to ions and a variety of organic molecules, projects inward into folds that are called cristae (singular crista). Embedded in this membrane are structures composed of molecular complexes and called respiratory assemblies (described in Chapter 10) that are responsible for the synthesis of ATP. Also present are a series of proteins that are responsible for the transport of specific molecules and ions. 

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