Question

2. Compare and contrast the structural and functional properties of myoglobin and hemoglobin How do they ensure that each plays their appropriate physiological role. Use this figure in your discussion. Justify your answer. (10 points) Working muscle Resting muscle 100 80 Myoglobin Hemoglobin Percent o, saturation 40 Arterial po Venous po 100 120 40 60 NO Partial pressure of oxygen (po, tor)

Answer 1

Hemoglobin is a heterotetrameric iron containing protein found in RBC facilitates transport of oxygen throughout the body. Whereas myoglobin is a monomeric protein facilitates intracellualr storage of oxygen in the muscle tissue. At the beginning of muscle activity, myoglobin desaturates that increases oxygen's diffusion gradient from the capillaries to the cytoplasm.

Myoglobin curve given in the graph is a rectangular hyperbola whereas the hemoglobin curve is a sigmoidal curve. Myoglobin lies left to hyemoglobin since it has much higher oxygen affinity.

Myoglobin has very lower P50 (2.75 mmHg) than hemoglobin P50 of PO2 of 25 mmHg. the physiologocal reason behind this is the fact that it can take away the oxygen delivered by hemoglobin. It also need to unload and load oxygen intracellularly also when the oxidative phosphorylation ceases below a pO2 of about 1 mmHg. This enable myoglobin to load oxygen from haemoglobin and can unload its oxygen as cytoplasmic pO2 falls to low levels.

Oxygen saturation is defined as the amount of hemoglobin that is currently bound to oxygen. When PO2 decreases, saturation % also drops.  When PO2 is at 100 mmHg, hemoglobin will be 100% saturated with oxygen.