differ in the precise genetic code used in protein synthesis. At least 13 movement of an ion down its electrochemical gradient. Linked trans-
respiratory chain enzymes of the matrix and inner membrane are port can be in the same direction as the solute, in which case the carrier
encoded by the small number of genes along the mitochondrial DNA. protein is described as a symporter, or in the opposite direction, when
The great majority of mitochondrial proteins are encoded by nuclear the carrier acts as an antiporter.
genes and made in the cytosol, then inserted through special channels
in the mitochondrial membranes to reach their destinations. Their Translocation of proteins across
membrane lipids are synthesized in the endoplasmic reticulum. intracellular membranes
It has been shown that mitochondria are of maternal origin because Proteins are generally synthesized on ribosomes in the cytosol or on
the mitochondria of spermatozoa are not generally incorporated the rough endoplasmic reticulum. A few are made on mitochondrial
into the ovum at fertilization. Thus mitochondria (and mitochondrial ribosomes. Once synthesized, many proteins remain in the cytosol,