## Practice Problems

### Questions on the Oxygen-Carrying Protein in the Blood: Hemoglobin

• One peptide subunit in hemoglobin contains 141 amino-acid residues. If the subunit were stretched out, it would measure approximately 49 nm in length. However, the longest dimension of the subunit in hemoglobin is only about 5 nm. Briefly, explain how alpha helices may help account for this difference in length. (help)
• What is the coordination number of Fe in the oxygenated heme group? Briefly, justify your answer by describing the ligands to which Fe is coordinated. (help)

### Questions on Conformational Changes Upon Binding of Oxygen:

• Explain, in terms of electron repulsion, why the heme group adopts a nonplanar (domed) configuration upon deoxygenation. (help)
• Explain how a change in the heme group configuration causes the entire hemoglobin subunit to change shape. (help)

### Questions on Spectroscopy and the Color of Blood

• Propose an explanation for why the change in heme group conformation results in a color change. (help)
• A researcher prepares two solutions of deoxygenated hemoglobin. One solution is ten times as concentrated as the other solution. The researcher then obtains absorption spectra for the two solutions. (help)
1. Do you expect the wavelength of maximum absorption (lmax) to be the same or different for the two solutions? If lmax is different for the two solutions, indicate which solution will have a higher lmax. Briefly, explain your reasoning.
2. Do you expect the absorbance (A) at lmax to be the same or different for the two solutions? If the absorbance is different for the two solutions, indicate which solution will have a higher absorbance. Briefly, explain your reasoning.

### Questions on the Bohr Effect:

• Does CO2 bind at the same site on the hemoglobin molecule as O2?  If not, where does CO2 bind? (help)
• In muscles, the oxygen released by hemoglobin is taken up by myoglobin. Myoglobin is a muscular protein that stores oxygen and allows it to diffuse throughout the muscle fibers so that it can be used by the muscle. Myoglobin contains only one subunit (and thus only one heme group), which is very similar to one of the subunits of hemoglobin. Would you expect myoglobin to exhibit the Bohr effect (i.e., would myoglobin release O2 in the presence of CO2 and H+)? Briefly, explain your reasoning.

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