Q-120. The conjugation of bilirubin to glucuronic acid in the liver:
a) Converts a hydrophilic compound to a hydrophobic one
b) Converts a hydrophobic compound to a hydrophilic one
c) Enables the bilirubin molecule to cross the cell membrane
d) Is increased during neonatal jaundice
Answer: Converts a hydrophobic compound to a hydrophilic one
Explanation:
Bilirubin is a tetra-pyrrole created by the normal breakdown of heme.
Most bilirubin is produced during the breakdown of hemoglobin and other hemo-proteins.
Because bilirubin is highly insoluble in water, it must be converted into a soluble conjugate before elimination from the body.
In the liver, uridine di-phosphate (UDP)-glucuronyl transferase converts bilirubin to a mixture of mono-glucuronides and di-glucuronides, referred to as conjugated bilirubin, which is then secreted into the bile by an ATP-dependent transporter.
The kidneys do not filter un-conjugated bilirubin because of its avid binding to albumin. For this reason, the presence of bilirubin in the urine indicates the presence of conjugated hyper-bilirubinemia.