This question depends on the type of material being broken down. For the time being, we'll assume that you are talking about food molecules. This is accomplished in three major stages. First, is the enzymatic breakdown of the foold molecules which happens in the lysosom. The large polymeric molecules in food are broekn down into smaller units (amino acids, sugars, fatty acids, etc). They move from these components into the cytosol where oxidation begins. In the second phase, glycolysis takes place and breaks down the food even further. From here they move into the mitochondria where they are attached to a carrier molecule. The last stage happens almost exclusively in the mitochondria and a series of chemical reactions takes place where the electrons are released and converted into ADP which becomes ATP for the cells.
