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.

transferrins - A group of specific transport proteins for ferric iron ions, transport proteins found within the beta globulin group of plasma proteins; cells that require iron have surface receptors to bind these specific iron transport proteins to accomplish the transfer of iron into the cell; because iron ions in the plasma are bound to these specific carriers and not simply dissolved in the water of plasma, they are much less accessible for use by invading microorganisms while also require iron and, therefore, these specific iron transport proteins act as a form of resistance to infection.

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