Structurally, hemocyanin is composed of many subunits containing imidazole rings of six histidine residues. Each subunit weighs about 75 kilodaltons kDa. Since there are many subunits, hemocyanin is a large molecule which has a high molecular weight compared to hemoglobin.
Furthermore, according to investigations, it has been found that hemocyanin is species-specific. Arthropods and mollusks have different types of hemocyanins. Hemoglobin Hgb is a vital metalloprotein molecule present in vertebrate red blood cells which transports oxygen from the lungs to other body tissues and carbon dioxide from the body tissues to the lungs.
Thus, it works as a respiratory pigment. Hemoglobin molecule is made up of four sub protein molecules in which two chains are alpha globulin chains and the other two are beta globulin chains. In each globulin chain, there is an iron-containing porphyrin compound called heme group. Within each heme group, there is an embedded iron atom. These iron-containing hemoglobin proteins are responsible for the red colour of the blood.
Structurally, haemoglobin is composed of C, H, N, and O. Hemoglobin is the main protein molecule which provides the typical shape of the red blood cell, that is the round shape with a narrow center. Iron atoms and the shape of the red blood cells are crucial for transporting oxygen through the blood. If the shape of hemoglobin is destroyed, it fails to transport oxygen. Sickle cell hemoglobin is one type of abnormal hemoglobin molecule which causes the anemia conditions called sickle cell anemia.
In normal hemoglobin, in beta chains, 6 th position of the amino acid chain is composed of glutamic acid. However, in sickle cell hemoglobins, 6 th position is taken up by a different amino acid called valine.
Though it is a single amino acid difference, it is responsible for this life-threatening anemia condition. Generally, hemoglobin shows a higher affinity for oxygen since there are four oxygen binding sites located inside a hemoglobin molecule.
Once hemoglobin molecule is saturated with oxygen, the blood becomes bright red in colour and this state is known as oxygenated blood.
The second state of the hemoglobin is known as deoxyhemoglobin which lacks oxygen. At this state, blood bears the dark red colour. Hemocyanin is a copper-containing protein present suspended in the hemolymph of invertebrates that transports oxygen within the body. On the other hand, hemoglobin is an iron-containing protein in the red blood cells of vertebrates which transports oxygen and carbon dioxide through the blood. So, this is the key difference between hemocyanin and hemoglobin.
Structurally, hemocyanin is composed of many protein subunits, while hemoglobin is composed of two alpha chains and two beta chains. Moreover, hemocyanin is a free-floating protein, while hemoglobin is bound to red blood cells.
Another important difference between hemocyanin and hemoglobin is that the central ion of hemocyanin is copper while the central ion of hemoglobin is iron. Most importantly, the colour of hemocyanin is blue while the colour of hemoglobin is red. Therefore, this another major difference between hemocyanin and hemoglobin. Preforms better in oxygen rich environments.
Contains copper held by a cluster. Contains iron held inside of a ring. Binds with oxygen non co-operatively most of the time when non co-operativly, is one quarter as efficiant as hemoglobin.
Binds with oxygen co-operatively all of the time. Free floating in blood. Connected to red blood cells. A model for hemoglobin Hemoglobin binds co-operativly with another hemoglobin, connected by two oxygen, much like the picture below of hemocyanin. What led to animals evolving Hemocyanin? Because Hemocyanin is less effective in most areas, people might wonder why any animal have Hemocyanin at all. Also Hemocyanin preforms better at colder temperatures, again where these molluscs and arthropods live.
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