Correct Answer - C
Some protein molecules contain as a part of their structure a nonprotein group (or nonpeptide portion) called a prosthetic group. Such proteins are called conjugated proteins. An example is the oxygen carrying proteins, haemoglobin. Each of the four polypeptide chains of four polypeptide chains of hemoglonin are wound in such a way as to give hameoglobin a roughly spherical shape.
The iron of the heme group is in the + 2 (ferrous) oxidation state and it form a coordinate bond to a nitrogen of the imidazole group of histidine of the polypeptide chain. This leaves one valence of the ferrous ion free to combine with oxygen. What is remarkable about hemoglogin is that when the heme combines with oxygen, the ferrous ion does not become readily oxidized to the ferric state.
