13 - NITROGEN METABOLISM 2025

Excretion of excess nitrogen seen in telostean fish, which excrete highly toxic ammonia

Ammonotelic

Seen in birds, which excrete uric acid as semisolid guano

Uricotelic

Seen in land animals, including humans, who excrete nontoxic water-soluble urea

Ureotelic

Organ where urea cycle mainly occurs

Liver

This substance functions solely as an enzyme activator and regulator of urea synthesis

N-acetylglutamate

Most common enzyme deficiency of the urea cycle

Ornithine transcarbomylase

Purely ketogenic amino acids

Lysine, Leucine

Glucogenic and ketogenic amino acids

Phenylalanine, Tyrosine, Isoleucine, Tryptophan

Deficient enzyme in phenylketonuria

Phenylalanine hydroxylase

Deficient enzyme in alkaptonuria

Homogentisate oxidase

Condition resulting from the darkening of the connective tissues in patients with alkaptonuria

Ochronosis

Deficient enzyme in albinism

Tyrosinase

Most common deficient enzyme in homocystinuria

Cystathionine β-synthase

Amino acids involves in cystinuria

Cystine, Ornithine, Lysine, Arginine

Deficient enzyme in maple syrup urine disease

α-ketoacid dehydrogenase complex

Amino acids involved in maple syrup urine disease

Isoleucine, Valine, Leucine

Rate-limiting enzyme of heme metabolism

δ-Aminolevulinic acid synthase

Lead inactivates these enzymes of heme metabolism

δ-Aminolevulinic acid dehydratase, Ferrochelatase