Question

This is a biochemistry question, please take the time to answer both questions and I will like as soon as the answer is posted. Thanks in advance!

QUESTION 7 From the graph below, identify the O2 binding curves for the following proteins. 100. a b % saturation 50 PO2 (torr) Hemoglobin A (HbA, P50 = 30 torr) - A mutated hemoglobin that has lost all cooperativity u HbA in presence of 8 mM BPG (elevated relative to normal [BPG] - Fetal hemoglobin (HbF) S HBA during hyperventilation - Y LA HBA during intense exercise

Answer 1

To answer this question, we need to understand the nature of binding of haemoglobin to Oxygen under different conditions. An oxygen binding curve or oxygen dissociation curve shows the relationship between partial pressure of oxygen in the blood and oxygen saturation of haemoglobin. The curve is sigmoid in shape and shifts its position to right or left depending on the affinity of haemoglobin to oxygen at different conditions. If affinity increases, the curve shifts to right and if it decreases the curve shifts to left. The shift depends mainly on factors like temperature, pCO2, 2,3BPG and pH.

The partial pressure of oxygen in the blood at which the haemoglobin is 50% saturated is known as the P50 value. In normal adult haemoglobin P50 is about 26.6 mmHg. But in our question, we are asked to find the curve of HbA with a P50 of 30 Torr. It is clear from the given graph that there is only one option, option C that matches this condition. Therefore c represents HbA.

Each haemoglobin molecule has 4 oxygen binding sites and can bind to 4 oxygen molecules. The affinity of haemoglobin to Oxygen increases as the number of hemes bound to oxygen in that molecule increases. This means that a Hb molecule with a single haeme bound to oxygen have more affinity to Oxygen than a completely deoxygenated Hb molecule. This property of haemoglobin is called cooperative binding. If this property of cooperative binding is lost by mutation or any other factors, the haemoglobin will show a lesser affinity to oxygen. This will shift the Oxygen binding curve to the right. Hence, the most suitable curve for a mutated haemoglobin that has lost all the cooperativity is option d (it is the only curve in the given graph that is shifted to right than the normal). Therefore d represents mutated haemoglobin without cooperativity.

2,3-Bisphosphoglycerate or 2,3-BPG is an organophosphate formed in erythrocytes during glycolysis. The normal concentration of 2,3BPG in human blood is 5mmol/L. But the concentration of 2,3 BPG increases in conditions where the peripheral tissue oxygen availability diminishes, as in case of high altitudes. The body compensates low oxygen availability by increasing red blood cell production, decreasing the binding affinity of haemoglobin and by increasing breathing rate. The binding affinity of Hb is decreased by the increased concentration of 2,3 BPG. Option d is the best match for HbA in presence of elevated 2,3 BPG.

Fetal Hb has greater affinity to Oxygen than adult Hb. This property is attributed to the presence of 2 gamma chains in HbF in place of the 2 beta chains in HbA. 2,3BPG that diminishes oxygen binding affinity binds to the beta chains in HbA and not to the gamma chains of HbF. Therefore HbF is unaffected by the presence of 2,3BPG and shows greater affinity. Due to this structural difference the oxygen binding curve of HbF is shifted to the left relative to HbA. The normal P50 of HbF is 19 mmHg. Therefore in the given graph, option b suits HbF the best.

During vigorous exercise, oxygen binding curve of Hb shifts to right, due to the following reasons: A decrease in pH (as the muscle cells gets more acidic), an increase in muscle temperature (from muscle contraction), an increase in the partial pressure of carbon dioxide (from the working muscles) and an increase in 2,3-BPG. Therefore option d indicates HbA during intense exercise.

Hyperventilation causes a left-shift of the curve which means that it leads to stronger affinity of oxygen to hemoglobin. During hyperventilation,more CO2 is released out than what is produced in the body. This reduces pCO2 and increases the pH. This causes a leftward shift in oxygen binding curve. Option a is the best match for hyperventilation.

• HbA - c
• Mutated Hb lacking cooperativity - d
• Hb in presence of elevated 2,3BPG - d
• HbF - b
• HbA during intense exercise - d
• HbA during hyperventilation - a