Which of the following is a characteristic of hemoglobin?
A) It is composed of four identical polypeptide chains.
B) There is one heme group per active Hb molecule.
C) Oxygen and carbon dioxide compete for the same binding site on heme.
D) It is an elongated, fibrous-type protein, hence is not very soluble in water.
E) Binding of oxygen to Hb results in change in the pKa of certain histidine residues toward lower values.

Question

Quizplus · Accepted Answer

Hemoglobin undergoes a conformational change upon oxygen binding, which affects the pKa of certain histidine residues, making them more likely to release protons. This is part of the Bohr effect, where oxygen binding is influenced by pH and CO2 concentration. Choices A, B, C, and D are incorrect because hemoglobin is composed of two alpha and two beta chains (not identical), has four heme groups (one per chain), oxygen and carbon dioxide bind at different sites (CO2 primarily binds to amino groups forming carbamino compounds), and it is a globular, not fibrous, protein, which contributes to its solubility in water.

Which of the Following Is a Characteristic of Hemoglobin