Question

In which organ is urea produced?

Answer 1

Urea is produced in the liver.

Explanation:

The body is unable to store proteins or amino acids, the products of protein metabolism.

When we ingest large amounts of protein, the excess amino acids from their digestion travel from the small intestine to the liver.

Here, the amino acids first undergo a process called transamination.

`underbrace("HOCOCH"_2"CH"_2"C"color(red)("O")"COOH")_color(red)("α-ketoglutaric acid") + underbrace("RCH"color(green)("NH"_2)"COOH")_color(red)("an α-aminoacid") stackrelcolor(blue)("a transaminase"color(white)(ml))(→) underbrace("HOCOCH"_2"CH"_2"CH"color(green)("NH"_2)"COOH")_color(red)("glutamic acid") + underbrace("RC"color(red)("O")"COOH")_color(red)("an α-ketoacid")`

In a process called oxidative deamination, the glutamic acid is converted back to α-ketoglutaric acid, with the release of ammonia.

`underbrace("HOCOCH"_2"CH"_2"CH"(color(green)("NH"_2))"COOH")_color(red)("glutamic acid") + "NAD"^+ + "H"_2color(red)("O") stackrelcolor(blue)("glutamate dehydrogenase"color(white)(m))(→)underbrace("HOCOCH"_2"CH"_2"C"color(red)("O")"COOH")_color(red)("α-ketoglutaric acid") + "NADH" + "H"^+ + color(green)("NH"_3)`

Ammonia is highly toxic to the body, so it cannot be allowed to accumulate.

The liver cells react carbon dioxide with the ammonia in a process called the ornithine cycle to form the less toxic compound, urea.

The overall reaction is

`2"NH"_3 + "CO"_2 + "3ATP" + "H"_2"O" → underbrace("H"_2"NCONH"_2)_color(red)("urea") + "2ADP" + "AMP" + "4P"_i`

The urea and water are released into the bloodstream and transported to the kidneys.

The kidneys filter the blood, and the water-soluble urea is excreted in the urine.