This animation shows a micrometre scale model of a mitochondrion (4 μm in length with a diameter of 500 nm) surrounded by the endoplasmic reticulum (ER). A major feature of the mitochondrial ultrastructure are the cristae which are folds extending from the mitochondrial inner membrane into the matrix. The two forms of cristae are shown: tubular and flattened sacs. Some of the cristae are depicted to be growing (mainly in the tubular form) whereas others are shown maintaining their shape. The change in size or shape of the cristae, like any other component of the mitochondria or other organelles, are dynamic processes maintained by proteins bound to the cristae membrane. The animation shows the main proteins that determine the shape, size and dynamics of the cristae, namely ATP synthase, Opa1 and a hypothetical model of the MICOS (mitochondrial contact site and cristae organising system) protein complex (see my website for more details). Other greatly important proteins that are mainly found on the cristae surface are the proteins involved in oxidative phosphorylation (Complex I, Complex II, Complex III, Complex IV and Complex V or the ATP synthase). This animation also shows other important molecules, namely cytochrome C, ATP/ADP carrier (ANT), the porin, (VDAC1) and mitoribosomes (mitochondrial ribosomes). The mitoribosomes are shown at two resolutions – a low resolution, electron microscopy-determined structure and one at high resolution detailing the protein synthesis. The animation of the function of the mitoribosome was based on a previous animation produced for Professor Sir Venki Ramakrishnan and on mitoribosome conformational states described by his group. This also shows ATP and ADP molecules as particles entering and exiting VDAC1 and the ATP/ADP carriers and being converted by the ATP synthase. For more details on the many structural and functional aspects of the mitochondria, please see other animations that I have produced in this YouTube channel.