In the liver, bilirubin is conjugated by the addition of which groups?

The correct answer is indeed the addition of glucuronyl groups to bilirubin in the liver. Bilirubin, which is a breakdown product of heme metabolism, is largely insoluble in water. To facilitate its excretion, bilirubin undergoes a process known as conjugation in the liver. This process increases its water solubility, allowing it to be excreted in bile and ultimately eliminated from the body.

In the liver, bilirubin is conjugated primarily by the addition of glucuronic acid, derived from the sugar glucose, to form bilirubin diglucuronide. This reaction is catalyzed by the enzyme UDP-glucuronosyltransferase. The presence of glucuronyl groups significantly enhances the solubility and helps transport bilirubin through the bile ducts into the intestine, where it can be further metabolized or excreted.

The other groups mentioned, such as sulfate, amino, and phosphate groups, do not play a primary role in the conjugation of bilirubin in the liver. While sulfate conjugation can occur for other substances, it is not the main pathway for bilirubin. Therefore, understanding that glucuronyl conjugation is essential for bilirubin's solubility and excretion is crucial