ATP can be formed during CELLULAR RESPIRATION , either in the general cytoplasm during GLYCOLYSIS or in the MITOCHONDRIA via the KREBS CYCLE and the ELECTRON TRANSPORT SYSTEM if oxygen is present. ATP is also formed during photosynthesis in the CHLOROPLASTS of green plants, again using an electron transport system. ATP molecules act therefore as short-term ‘biological batteries’, retaining energy until required for such processes as active transport, synthesis of new materials, nerve transmission, and muscle contraction. An active cell requires more than two million molecules of ATP per second to drive its biochemical machinery.
Acetyl coenzyme A or acetyl-CoA is a molecule that participates in many biochemical reactions in protein, carbohydrate and lipid metabolism .  Its main function is to deliver the acetyl group to the citric acid cycle (Krebs cycle) to be oxidized for energy production. Coenzyme A (CoASH or CoA) consists of a β-mercaptoethylamine group linked to the vitamin pantothenic acid through an amide linkage.  The acetyl group (indicated in blue in the structural diagram on the right) of acetyl-CoA is linked to the sulfhydryl substituent of the β-mercaptoethylamine group. This thioester linkage is a "high energy" bond, which is particularly reactive. Hydrolysis of the thioester bond is exergonic (− kJ/mol).
The liver also plays an important role in vitamin and mineral ( iron & copper ) storage. About 80% of the body's vitamin A stores are concentrated in fat droplets within the stellate cells of the liver. In pathological conditions like hepatic fibrosis or liver cirrhosis the stellate cells lose vitamin A, transform into fibroblasts or myofibroblasts and begin producing large amounts of collagen and adhesive glycoproteins. * Normal vitamin A reserves are enough to prevent a deficiency for about 10 months. The liver also contains about a year supply of B12. Vitamin D stores equal about 3-4 months. Small amounts of Vitamins E and K and Vitamin C are stored in the liver to facilitate liver functions.