In eukaryotes electron transport and oxidative phosphorylation occur in the inner membrane of mitochondria. These processes reoxidise NADH2 and FADH2 and trap the energy to form ATP. The matrix of mitochondria contains the enzymes of Krebs cycle during which acetyl Co? A is oxidised to H2O and CO3 with reduction of NAD and FAD. Endoplasmic reticulum contains ribosomes on its surface which are the site of protein synthesis. The protein molecules passes to endoplasmic reticulum lumen where folding takes place.