Question

Consider defects in the aromatic amino acid catabolism.

a) Why are patients with phenylketonuria not complete albinos?

b) Explain why an early diagnosis of phenylketonuria would be able to spare the patients from the deleterious

effects of the disease, while an early diagnosis of albinism would not.

Answer 1

Answer-

According to the given question-

We know that each protein or polypeptide present in the body codes for a different gene. each enzyme protein which are involved in metabolic pathway also coded by different gene but inherited defect in these genes causes disease called  inborn error of metabolism.

We know that a protein is produced following several steps and intermediates with the help of several enzymes but in this case the amount of  intermediates formed before the defective enzymatic catalysis step is increases while the amount of   intermediates as well as final products that are formed after the defective enzyme catalysis step is decreases and the diseases occue is due to the lack of  normal end product or due to  accumulation of high amount of intermediates formed before the defective enzyme catalysis step. we know that Several enzymes follow linear pathway while some follow branch pathway for catalysis of reaction. if the defective enzyme follows the branch pathway then the intermediates as well as end  products of all the alternate pathway arises from thi step will increase and leads to  metabolic diseases.

Aromatic enzyme phenylalanine is converted into dihydroxyphenylalanine or DOPA which is a precursor of   pigment molecule called melanin responsible for giving normal color to eyes, skin, as wll as hair.Albinism which is an inherited defect where the enzyme that convert dihydroxyphenylalanine into melanin .phenylketonuria or PKU occur when there is a defect in enzyme Phenylalanine hydroxylase converting phenylalanine  amino acid into tyrosine amino acid leads to formation of defective final product and accumulated. these accumulated products are observe in blood and urine. PKU is responsible for shortened life span and mental retardation. But if we can detect the disease early during newborn development we prevent the mental retardation condition by giving child low level of phenylalanine diet. But in case of albanism which is a congenital disorder acquired during fetal development so it can not be cures by changing the concentration of tyrosinase or DOPA.

where b = Phenylalanine hydroxylase, f = Tyrosinase.

lack of enzyme b causes Phenylketonuria while lack of enzyme f causes Albanism.