Question

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Compare and contrast the oxygen binding pockets of myoglobin and hemoglobin.

Answer 1

Myoglobin oxygen binding:- Haem is important biologically in myoglobin which is used to store dioxygen in muscles. It is similar to one of the unit in haemoglobin. It contains only one iron and binds oxygen more strongly than haemoglobin. Myoglobin contains a single polypeptide chain and single iron porphyrin group identical to haemoglobin. Oxygen binded to myoglobin are transported to mitochondria, which consume oxygen during respiration.

Haemoglobin oxygen binding:- Haemoglobin comprise four myoglobin like subunit (not myoglobin). Each subunit of haemoglobin contains a polypeptide chain and a heme group coordinated through the nitrogen atom of the histidine group of its polypeptide chain. Haemoglobin picks up oxygen from lungs and carries it to the muscle tissue via the circulatory system. The oxygenated Haemoglobin then transfers the oxygen to the myoglobin present in the muscle tissue, where it remains stored till it is transferred to other oxygen acceptors for performing metabolic actions in the biological system. Apart from acting as oxygen carriers, Haemoglobin has an additional function of carrying carbon dioxide from worked up muscle tissue to the lungs. This is done by certain side chain present on the polypeptide chains of Haemoglobin.

Myoglobin binds Oxygen more tightly than haemoglobin because the binding power of Haemoglobin is pH dependent and myoglobin is not dependent. The decrease in pH favours the transfers of oxygen to myoglobin and carbon dioxide to Haemoglobin.