Hemoglobin:Theoxygen-carryingpigmentand predominantproteininthe red blood cells. Hemoglobin forms an unstable, reversible bond with oxygen. In its oxygenated state it is calledoxyhemoglobin明亮的红色。在e reduced state it is calleddeoxyhemoglobinand is purple-blue.
Each hemoglobinmoleculeis made up of four heme groups surrounding a globin group. Heme containsironand gives a red color to the molecule. Globin consists of two linked pairs ofpolypeptidechains. Thedevelopmentof each chain is controlled at a separategeneticlocus。的变化amino acidsequence of these chains results inabnormalhemoglobins. For example,hemoglobin Sis found in sickle-celldisease, a severe type of anemia in which the red cells become sickle-shaped when oxygen is in short supply.
When redbloodcells die, the hemoglobin within them is released and broken up: the iron in hemoglobin is salvaged, transported to thebone marrowby a protein calledtransferrinand used again in the production of new red blood cells; the remainder of the hemoglobin becomes a chemical called bilirubin that is excreted into thebilewhich is secreted into theintestine, where it gives thefecestheir characteristic yellow-brown color.
