What is true of urea biosynthesis?

Question

What is true of urea biosynthesis? (A) Uric acid is starting point (B) Urea is synthesized in lysosomes (C) Urea cycle enzymes are located inside mitochondria (D) Urea is synthesized in kidney

Tardigrade Admin · Accepted Answer

Urea cycle was discovered by Krebs and Hanseleit
• Urea cycle takes place in liver cells
• In urea cycle,

N H_{3}

is converted into urea
• In urea cycle, 2 molecules of

N H_{3}

and 1 molecule of

C O_{2}

is involved
• Urea cycle removes two waste products from the blood in liver, i.e.

N H_{3}

and

C O_{2}

• Urea

(N H_{2} - CO - N H_{2})

has 2 amino

(- N H_{2})

groups, one derived from

N H_{3}

and other from aspartate
• C-atom of urea is supplied by

C O_{2}

• One molecule of

N H_{3}

and one molecule of

C O_{2}

react to form carbamoyl phosphate. Carbamoyl phosphate reacts with ornithine to form citrulline
• Citrulline reacts with aspartate to produce ar-ginosuccinate Arginosuccinate cleaves to give fumarate and arginine. Arginase cleaves to arginine to form urea and ornithine
• Ornithine is reused in urea cycle. Urea is transported to kidney for its removal
• 3 amino acids participating in urea cycle are ornith - ine, citrulline and arginine

Q. What is true of urea biosynthesis?

Uric acid is starting point

Urea is synthesized in lysosomes

Urea cycle enzymes are located inside mitochondria

Urea is synthesized in kidney