AIIMS Bhuvneshwar NO…: In liver, Bilirubin is conjugated with?

AIIMS Bhuvneshwar NO- 2018

Biochemistry & Nutrition

Easy

Appeared in: AIIMS Bhuvneshwar NO- 2018

Explanation

In the liver, unconjugated bilirubin is made water-soluble through a process called conjugation.
The enzyme UDP-glucuronyltransferase (UGT1A1), located in the endoplasmic reticulum of hepatocytes, catalyzes this reaction.
This enzyme attaches glucuronic acid to the bilirubin molecule, forming bilirubin monoglucuronide and diglucuronide.
This conjugated form of bilirubin is water-soluble and can be excreted into the bile for elimination from the body.

Option A: Bile acids are components of bile that aid in fat digestion. They are not involved in the conjugation of bilirubin.
Option B: Glutamic acid is an amino acid and plays no role in the conjugation of bilirubin.
Option C: Cholic acid is a primary bile acid. Like other bile acids, its role is in fat emulsification, not bilirubin conjugation.

Visual 1: Flowchart - A diagram illustrating the complete pathway of bilirubin metabolism, from heme breakdown in reticuloendothelial cells to conjugation in the liver and final excretion in stool and urine. This helps visualize each step, including the key role of glucuronic acid.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Bilirubin metabolism and conjugation in the liver as background academic context rather than a clinical decision trigger.
Understanding bilirubin conjugation is crucial for assessing liver function and diagnosing different types of jaundice.
In neonatal jaundice, the UGT1A1 enzyme is immature, leading to a buildup of unconjugated bilirubin. Nurses monitor bilirubin levels and administer phototherapy, which converts bilirubin into a water-soluble form that can be excreted without conjugation.
Elevated conjugated bilirubin in the blood suggests a problem with excretion from the liver (cholestasis) or bile duct obstruction, whereas elevated unconjugated bilirubin points to overproduction (hemolysis) or a conjugation problem (e.g., Gilbert syndrome).

How to Approach the Question

First, identify the core of the question, which is asking about a specific biochemical process: bilirubin conjugation.
Recognize this as a factual recall question related to liver physiology and metabolism.
Recall the steps of bilirubin metabolism. Focus on the transition from a lipid-soluble (unconjugated) molecule to a water-soluble (conjugated) one, which happens in the liver.
Identify the specific substance that the liver adds to bilirubin to make it water-soluble. This is the key to the answer.
Evaluate the options: 'Bile acids' and 'Cholic acid' are related to liver function but for fat digestion. 'Glutamic acid' is an amino acid. 'Glucuronic acid' is the correct substrate for conjugation.
Select the option that correctly identifies the conjugating agent.

Concept Tested & Keywords

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E6 Harper's Illustrated Biochemistry 32nd Edition 2023 (pp 26-793 of 813) p. 793-813