Question

Melanurea(black urine) is caused by abnormal catabolism of

• A. Alanine
• B. Tyrosine
• C. Proline
• D. Tryptophan

Answer 1

The correct option is B Tyrosine

Mutations in the HGD (homogentisate 1,2-dioxygenase) gene cause alkaptonuria ( inherited condition that causes urine to turn black when exposed to air). The HGD gene provides instructions for making an enzyme called homogentisate oxidase. This enzyme helps break down the amino acids phenylalanine and tyrosine, which are important building blocks of proteins. Mutations in the HGD gene impair the enzyme's role in this process. As a result, a substance called homogentisic acid, which is produced as phenylalanine and tyrosine are broken down, accumulates in the body. Excess homogentisic acid and related compounds are deposited in connective tissues, which causes cartilage and skin to darken. Over time, a buildup of this substance in the joints leads to arthritis. Homogentisic acid is also excreted in urine, making the urine turn dark when exposed to air.

So, the correct answer is 'Tyrosine'.