Ans. D. In the mitochondrial matrix and the cytosolThe steps of the urea cycle are divided between the mitochondrial matrix and cytosol of liver cells in mammals. The formation of ammonia, its reaction with carbon dioxide to produce carbamoyl phosphate, and the conversion to citrulline occur in the matrix of mitochondria. Citrulline diffuses out of the mitochondria, and the next three steps of the cycle, which result in the formation of urea, all take place in the cytosol. Peroxisomes have single membranes, in contrast to the double membranes of mitochondria. They house catalase and enzymes for medium- to long-chain fatty acid oxidation.METABOLIC PATHWAYSITE OF OCCURRENCEGlycolysisCytosolKrebs/TCA/Citric acid cycleMitochondrial matrixGluconeogenesisPartly in cytosol and in mitochondriaGlycogenolysis and GlycogenesisCytosolHMP shuntCytosolProtein synthesisCytosolUrea cyclePartly in cytosol and in mitochondriaTriacylglycerol biosynthesisEndoplasmic reticulum(some are biosynthesized in mitochondria)Ether phospholipids, Plasmalogens and PAFs biosynthesisPeroxisomesSphingolipid biosynthesisEndoplasmic reticulumSphingomyelin biosynthesisGolgi apparatus > Plasma membraneGlycosphingolipid (Cerebrosides and Gangliosides) biosynthesisGolgi apparatusCholesterol biosynthesisEndoplasmic reticulum > CytosolFatty acid biosynthesisCytosolMonounsaturated fatty acid biosynthesisEndoplasmic reticulumCeramide biosynthesis from serineEndoplasmic reticulumBile acid biosynthesisCytosolN-Linked Glycoside biosynthesisEndoplasmic reticulumO-Linked Glycoside biosynthesisGolgi apparatusGlycosaminoglycans biosynthesisGolgi apparatusElongation of fatty acid chainsEndoplasmic reticulumFatty acid oxidationMitochondriaOxidation of very long chain Fatty acidsPeroxisomes (initially until it reaches the Octenyl stage)