Chapter 7 Hemoglobin:A Portrait of a Protein in Action 8 Short-Answer Questions 39.Why is it advantageous for hemoglobin to have allosteric properties? Ans:Hemoglobin binds oxygen in a positive cooperative manner.This allows it to become saturated in the lungs,where oxygen pressure is high.When the hemoglobin moves to tissues,the lower oxygen pressure induces it to release oxygen and thus deliver oxygen where it is needed. Section:7.1 40.What is fetal hemoglobin?How does it differ from adult hemoglobin? Ans:Fetal hemoglobin contains two a and two y chains,in contrast to adult hemoglobin with two a and two B chains.The fetal hemoglobiny chain is probably a result of gene duplication and divergence.The difference in the chains results in a lower binding affinity of 2-3 BPG to fetal hemoglobin.Thus,the fetal hemoglobin has a higher affinity for oxygen,and the oxygen is effectively transferred from the mother's hemoglobin to fetal hemoglobin. Section:7.2 41.What is metmyoglobin? Ans:Metmyoglobin is formed when the heme iron ion,which is normally in the +2 oxidation state,is oxidized to the +3 oxidation state.This oxidized form of myoglobin does not bind dioxygen and is not functional. Section:7.1 42.Describe the octahedral coordination sphere of the iron ion in hemoglobin and myoglobin. Ans:The Fe+2 ion is coordinated to the four nitrogens in the center of the protoporphyrin of the heme.The fifth coordination site is occupied by the "proximal histidine"of the globin chain.The oxygen is bound to the sixth coordination site of the iron. Section:7.1 43.What functional role does the"distal histidine"play in the function of myoglobin and hemoglobin? Ans:The bonding between the iron and oxygen can be described as a combination of resonance structures,one with Fe2+and dioxygen and another with Fe and superoxide. The"distal histidine"donates a hydrogen bond to this complex stabilizing the complex and inhibits the oxidation of the iron to the ferric state. Section:7.1Chapter 7 Hemoglobin: A Portrait of a Protein in Action 8 Short-Answer Questions 39. Why is it advantageous for hemoglobin to have allosteric properties? Ans: Hemoglobin binds oxygen in a positive cooperative manner. This allows it to become saturated in the lungs, where oxygen pressure is high. When the hemoglobin moves to tissues, the lower oxygen pressure induces it to release oxygen and thus deliver oxygen where it is needed. Section: 7.1 40. What is fetal hemoglobin? How does it differ from adult hemoglobin? Ans: Fetal hemoglobin contains two  and two  chains, in contrast to adult hemoglobin with two  and two  chains. The fetal hemoglobin  chain is probably a result of gene duplication and divergence. The difference in the chains results in a lower binding affinity of 2-3 BPG to fetal hemoglobin. Thus, the fetal hemoglobin has a higher affinity for oxygen, and the oxygen is effectively transferred from the mother’s hemoglobin to fetal hemoglobin. Section: 7.2 41. What is metmyoglobin? Ans: Metmyoglobin is formed when the heme iron ion, which is normally in the +2 oxidation state, is oxidized to the +3 oxidation state. This oxidized form of myoglobin does not bind dioxygen and is not functional. Section: 7.1 42. Describe the octahedral coordination sphere of the iron ion in hemoglobin and myoglobin. Ans: The Fe +2 ion is coordinated to the four nitrogens in the center of the protoporphyrin of the heme. The fifth coordination site is occupied by the “proximal histidine” of the globin chain. The oxygen is bound to the sixth coordination site of the iron. Section: 7.1 43. What functional role does the “distal histidine” play in the function of myoglobin and hemoglobin? Ans: The bonding between the iron and oxygen can be described as a combination of resonance structures, one with Fe 2+ and dioxygen and another with Fe 3+ and superoxide. The “distal histidine” donates a hydrogen bond to this complex stabilizing the complex and inhibits the oxidation of the iron to the ferric state. Section: 7.1