Chemical chemistry

Question 1

Haem oxygenase

Answer 1

Enzyme that oxidises haem to biliverdin.

Biliverdin is green.

Question 2

Biliverdin reductase

Answer 2

Enzyme that reduces biliverdin to bilirubin.
- This process requires NAPDH.

Biliverdin is green
Bilirubin is yellow and not water soluble.

Question 3

Haem degradation in macrophages

Answer 3

This occurs in the spleen:

1. Haem oxidises—-> Biliverdin
   - Using haem oxygenase
2. Biliverdin reduces—-> Bilirubin
   - Uses biliverdin reductase

Bilirubin is then bound to albumin and transported to the liver.

Question 4

Bilirubin metabolism in the liver

Answer 4

Bilirubin is brought to the liver bound to albumin, from the spleen.

Bilirubin is conjugated with glucuronic acid to produce bilirubin diglucuronide (water soluble)

Conjugated bilirubin is excreted out the liver in bile.

Question 5

Bilirubin metabolism in the intestines.

Answer 5

Bile contain conjugated bilirubin enters the small intestines.

Bacteria in SI deconjugate bilirubin to form urobilinogen (colourless).

Urobilinogen is processed further in the intestines to stercoblin which makes faeces brown.

Some urobilinogen is reabsorbed from the SI and removed from the blood.
- Excreted in the urine as urobilin, making urine yellow/amber.