Heme degradation

Question 1

Site of RBC degradation

Answer 1

Reticuloendothelial system, particularly in the liver and spleen

Question 2

Step 1

• Reaction
• Enzyme

Answer 2

• Reaction
  
  • Heme → biliverdin (green) → bilirubin (red-range)
• Enzyme
  
  • Heme oxygenase system of reticuloendothelial cells

Question 3

1. Bilirubin is transported to the liver by binding to ____
2. In the liver, bilirubin binds to ____

Answer 3

1. Albumin
2. Intracellular protein ligandin

Question 4

Formation of bilirubin diglucoronide

• Process
• Enzyme

Answer 4

• Process
  
  • Bilirubin is conjugated to 2 molecules of glucuronic acid
• Enzyme
  
  • Bilirubin glucuronyltransferase

Question 5

If bilirubin ‘colors’ the stool and urine, why are they not red-orange as is the color of bilirubin?

Answer 5

• Intestines
  
  • Bilirubin → urobilinogen (colorless) → intestinal bacteria oxidize urobilinogen → stercolin (brown)
• Kidney
  
  • Some urobilinogen reabsorbed from blood → converted to urobilin (yellow) in the kidney