A crista (; plural cristae) is a fold in the inner membrane of a mitochondrion. The name is from the Latin for crest or plume, and it gives the inner membrane its characteristic wrinkled shape, providing a large amount of surface area for chemical reactions to occur on. This aids aerobic cellular respiration, because the mitochondrion requires oxygen. Cristae are studded with proteins, including ATP synthase and a variety of cytochromes. With the discovery of the dual-membrane nature of mitochondria, the pioneers of mitochondrial ultrastructural research proposed different models for the organization of the mitochondrial inner membrane. Three models proposed were:
- Baffle model – According to Palade, the mitochondrial inner membrane is convoluted in a baffle-like manner with broad openings towards the intra-cristal space. This model entered most textbooks and was widely believed for a long time.
- Septa model – Sjöstrand suggested that sheets of inner membrane are spanned like septa (plural of septum) through the matrix, separating it into several distinct compartments.
- Crista junction model – Daems and Wisse proposed that cristae are connected to the inner boundary membrane via tubular structures characterized by rather small diameters, termed crista junctions (CJs). These structures were rediscovered recently by EM tomography, leading to the establishment of this currently widely accepted model.