1 Human erythrocytes (red blood cells) Erythrocytes are small disk-shaped cells in the blood. They have lost their intracellular organelles, can not reproduce and survive about 4 months. Erythrocytes contain 34% hemoglobin by weight. Blood is oxygenated at the lungs, where Hemoglobin is 95%+ saturated with O 2. As blood passes through the tissues, hemoglobin releases O 2 and is now as low as 35% saturated with O 2.

2 Hemoglobin releases O 2 and binds CO 2, H + in extremities O2O2 O2O2 CO 2 H + Hemoglobin releases CO 2 at lungs and binds O 2. Lung pH = 7.6 Tissue pH = 7.2

3 Bohr Effect Hemoglobin carries oxygen from the lungs to the tissues for cellular respiration. Hemoglobin carries CO 2 and H +, byproducts of cellular respiration, back to the lungs and kidneys for excretion. In erythrocytes CO 2 is converted to HCO 3 - by carbonic anhydrase. CO 2 + H 2 O H + + HCO 3 - This results in a decrease in pH in the tissues. At low pH hemoglobin binds H + and CO 2 and the affinity for O 2 decreases. O 2 is therefore released in the tissues as CO 2 and H + are bound.

Regulation of O 2 binding by 2,3-Bisphosphoglycerate The molecule 2,3-bisphosphoglycerate (BPG) is bound by hemoglobin and lowers the affinity for O 2. If there is an increase in BPG in the blood, hemoglobin will have a lower O 2 affinity and will release more O 2 in the tissues. At high altitudes where O 2 is depleted we produce more BPG to deliver more oxygen to the tissues.

BPG binds to hemoglobin at a site distant from the oxygen binding site of hemoglobin.

Fraction of hemoglobin with bound oxygen BPG lowers the oxygen affinity of hemoglobin

Fetal Hemoglobin A fetus must extract O 2 from the mother’s blood. A fetus has  hemoglobin subunits instead of  subunits. The  2  2 fetal hemoglobin has a lower affinity for BPG than  2  2 adult hemoglobin Therefore  2  2 fetal hemoglobin has a higher affinity for O 2.

8 Normal Erythrocytes Sickle-cell anemia Glu 6 Val 6

In sickle-cell anemia hemoglobin S molecules aggregate and form insoluble crystalline fibers. This gives the erythrocyte a “sickle” shape

12 State whether each of the following will increase or decrease the affinity of hemoglobin for oxygen. Change in blood pH from 7.2 to 6.8 Change in pCO 2 from 36 torrs to 12 torrs Change in the blood 2,3-bisphosphoglycerate [BPG] concentration from 2 x M to 8 x M Climbing up Mount Everest from 1,000 meters above sea level to 4,000 meters above sea level Change in blood proton [H + ] concentration from 1.8 x M to 2.1 x M

13 Indicate whether each of the following statements about hemoglobin and myogobin is true or false. Hemoglobin is present in red blood cells (erythrocytes) Myoglobin is abundant in mammalian muscle tissue. Myoglobin is a tetrameric protein with four protein subunits. Hemoglobin is a structural protein whose function is to give erythrocytes their disk shape. Hemoglobin has four identical protein subunits, each designated as alpha (  ). Hemoglobin and myoglobin both contain a prosthetic group called a heme. Hemoglobin utilizes a bound zinc (Zn 2+ ) ion to bind oxygen. Hemoglobin has a higher affinity for oxygen at pH 7.2 than at pH 7.6. Hemoglobin has a lower affinity for oxygen when CO2 is present in high concentrations in the blood.

Challenge Question 14 Myoglobin and the individual subunits of hemoglobin are similar in size, shape, and function. Would you expect a molecule of myoglobin or hemoglobin to have a greater ratio of nonpolar to polar amino acids? Why?