Exam 1 Review:  Chapter 17:  Hemoglobin and Iron Metabolism

hemoglobin - The iron-containing respiratory pigment in red blood cells, consisting of about 6% heme (the lipid prosthetic group which binds the iron) and 94 % globin (the four polypeptide chains*, two alpha and two beta chains); the main function of the molecule is to bind and transports 4 oxygen molecules; it plays a lesser role in carbon dioxide transport and is also a blood buffer, capable of binding hydrogen ions.  [*Note:  different chains are found in fetal, embryonic, and mutant hemoglobins.]

heme - The complex red organic pigment, a lipid (porphyrin) containing iron, which is present in four copies as prosthetic groups bound to the globin chains of the hemoglobin molecule; when recycled it is converted to bilirubin and excreted in the bile.

globin - The family of related proteins with quaternary structure (e.g., two alpha and two beta chains) which is the protein constituent of the oxygen-binding molecules, hemoglobin and myoglobin.

hemoglobin alpha chain = alpha unit = alpha globin - One of the two similar polypeptide chains which combine in pairs to form the globin portion of the hemoglobin molecule; each alpha chain consists of 141 amino acids; each chain is conjugated with an iron-containing heme group which binds oxygen.

hemoglobin beta chain = beta unit = beta globin - One of the two similar polypeptide chains which combine in pairs to form the globin portion of the hemoglobin molecule; each beta chain consists of 146 amino acids; each chain is conjugated with an iron-containing heme group which binds oxygen; the mutation which produces sickle cell anemia is in the beta chain.

transferrin - A specific transport protein for ferric iron ions found within the beta globulin group of plasma proteins; cells that require iron have surface receptors to bind transferrin to accomplish the transfer of iron into the cell.

ferritin - An iron-containing (20%) protein complex, found principally in the intestinal mucosa, spleen, and liver, which functions as the primary form of iron storage in the body; iron stored in this molecule is available to the body for use.

hemosiderin - A granular brown protein complex containing ferric oxide; left from the breakdown of hemoglobin; iron stored in this molecule is not available to the body for use; its presence in cells in significant amounts can be a sign of disturbed iron metabolism.

bilirubin - An orange-yellow lipid pigment excreted by the liver into the bile which forms as a by-product of hemoglobin breakdown and recycling; excess amounts in the blood or deposited in tissues produce the yellow appearance observed in jaundice.

urobilinogen - A minor waste molecule, the product of the microbial breakdown of bilirubin (bilirubin is a waste product of the breakdown of the heme in hemoglobin) by intestinal normal flora which is water-soluble and is absorbed from the intestine and then excreted into the urine.

List:

7. The three important substances (chemicals) transported by hemoglobin.

          oxygen gas O₂ - carbon dioxide gas CO₂ - hydrogen ion H⁺

Describe:

2. The components of hemoglobin.

protein:  2 alpha and two beta chains joined in quaternary structure

4 (lipid) heme groups, one attached to each α & β chain

4 iron ions (Fe2+), one attached to each heme group