Question

Defect in amino acid metabolism may result in.
(a) Porphyria
(b) Phenylketonuria
(c) Wilson’s disease
(d) Tay Sach’s disease

Answer 1

Hint: The disorder that causes a defect in the amino acid metabolism occurs due to mutations in both the alleles of a gene that is present on chromosome number 12. Due to this mutation, the enzyme required for amino acid metabolism is not produced.

Complete Answer:
The defect in the metabolism of the amino acid phenylalanine results in Phenylketonuria. Phenylketonuria PKU is an autosomal recessive disorder i.e. it is inherited from parents to children. This happens due to a mutation on chromosome 12 because of which the enzyme phenylalanine hydroxylase (PAH) is not produced in the body. This enzyme is responsible for converting phenylalanine into tyrosine and in its absence phenylalanine gets accumulated. This further gets converted into phenyl pyruvic acid which causes mental retardation.

Additional information: Let us look at the other disorders mentioned in the options.
Porphyria: It is a type of liver disorder in which a compound named porphyria gets accumulated in the body resulting in the deterioration of the skin and nervous system.
Wilson’s disease: It is a type of genetic disorder in which there is excess copper metal build up in the body which affects the functioning of the brain and the liver.
Tay Sach’s disease: It is also a genetic disorder that results in the destruction of nerve cells present in the brain and the spinal cord which results in the loss of the ability to sit, walk or even crawl.
So, the correct option is ‘(b) Phenylketonuria’.

Note:
- Phenyl pyruvic acid is excreted through the urine as well because of their poor absorption by the kidneys.
- Other autosomal recessive disorders include sickle cell anemia in which the RBC becomes sickle-shaped due to a mutation in the hemoglobin.
- Another autosomal recessive disorder is thalassemia which is also a blood disorder caused because of abnormal hemoglobin.