Phenylketonuria (PKU) can be defined as a rare metabolic disorder caused by a deficiency in the production of the hepatic (liver) enzyme phenylalanine hydroxylase (PAH). PKU is the most serious form of a class of diseases referred to as hyperphenylalaninemia, all of which involve above normal (elevated) levels of phenylalanine in the blood.
All organisms carry out cellular respiration (except viruses) - it is the basic process which supports life as we know it. Viruses, on the other hand, are not always câ¦onsidered to be living, one of the reasons being that they do NOT carry out cellular respiration.
* cellular respiration (releasing the chemical energy of glucose to form ATP which is used for energy) can happen with or without oxygen (O2). ANAEROBIC RESPIRATION--does not use O2. AEROBIC RESPIRATION--uses O2; most organisms carry out aerobic respiration.