The waste product bilirubin is formed from:
(a) Transferrin
(b) Globin
(c) Heme
(d) Hemosiderin
(e) Ferritin

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Understand that bilirubin is a waste product formed during the breakdown of red blood cells, specifically from the degradation of hemoglobin components.

Recall that hemoglobin consists of two main parts: globin (a protein) and heme (an iron-containing compound).

Recognize that globin is broken down into amino acids, which are reused by the body, so it is not the source of bilirubin.

Identify that heme is broken down into iron and biliverdin, which is then converted into bilirubin, making heme the direct precursor of bilirubin.

Conclude that among the options, bilirubin is formed from heme, not from transferrin, globin, hemosiderin, or ferritin.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Bilirubin Formation

Bilirubin is a yellow pigment formed during the breakdown of heme, a component of hemoglobin in red blood cells. It is produced when heme is degraded by the enzyme heme oxygenase, releasing iron and converting the heme ring into biliverdin, which is then reduced to bilirubin.

Heme Structure and Function

Heme is an iron-containing compound found in hemoglobin and other hemoproteins. It binds oxygen in red blood cells and is composed of a porphyrin ring with a central iron atom. Its breakdown is essential for recycling iron and producing bilirubin.

Role of Globin and Iron Storage Proteins

Globin is the protein part of hemoglobin that carries oxygen, which is broken down separately from heme. Iron released from heme degradation is stored in proteins like ferritin and hemosiderin, which regulate iron availability and prevent toxicity.

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