Chapter 9 Reading Quiz and Homework

In comparison to that of adult hemoglobin, how is the fetal oxygen-hemoglobin dissociation curve shifted?

to the left of the adult curve, indicating a higher oxygen affinity of fetal hemoglobin

Suppose Gina climbs a high mountain where the oxygen partial pressure in the air decreases to 80 torr. Assume that the pH of her tissues and lungs is 7.4 and the oxygen concentration in her tissues is 20 torr. The P50 of hemoglobin is 26 torr. The degree of cooperativity of hemoglobin, n, is 2.8. Estimate the percentage of the oxygen‑carrying capacity that she utilizes. Calculate your answer to one decimal place. After Gina spends a day at the mountaintop, where the oxygen partial pressure is 80 torr,80 torr, the concentration of 2,3‑bisphosphoglycerate (2,3‑BPG) in her red blood cells increases. Why does increasing the concentration of 2,3‑BPG in Gina's blood cells help her function well at high altitudes?

Capacity: 64 Her oxygen‑binding curve shifts to the right, promoting oxygen delivery to tissues.

In addition to transporting oxygen from the lungs to the tissues, hemoglobin is also involved in transporting carbon dioxide from the tissues to the lungs. How does hemoglobin transport carbon dioxide from the tissues to the lungs?

Carbon dioxide reacts with an amino group, stabilizing the R state.

The illustration shows several oxygen‑dissociation curves. Assume that curve 3 corresponds to hemoglobin with physiological concentrations of CO2 and 2,3-bisphosphoglycerate (2,3-BPG) at pH 7. Curve 1 increases rapidly, Curve 4 increases the least rapidly. Saturation is on the Y-axis. pO2 is on the X-axis.

Curve 1 - a loss of quaternary structure Curve 2 - decrease in CO2, an increase in pH Curve 3 - no perturbation Curve 4 - an increase in 2,3-BPG

Which molecules are bound to hemoglobin when hemoglobin is in the R state?

Fe 2+ Oxygen

What is the molecular consequence of the hemoglobin S mutation?

Hemoglobin S forms aggregates and fibrous precipitates when oxygen is released.

How does hemoglobin function as a pH buffer?

Hemoglobin binds hydrogen ions after carbon dioxide enters the red blood cell.

Select all statements that correctly describe hemoglobin and myoglobin structure.

Hemoglobin is a heterotetramer, whereas myoglobin is a monomer. Each iron atom can form six coordination bonds. One of these bonds is formed between iron and oxygen. Both hemoglobin and myoglobin contain a prosthetic group called heme, which contains a central iron (Fe) atom. By itself, heme is not a good oxygen carrier. It must be part of a larger protein to prevent oxidation of the iron.

For the given changes in environment, choose whether the oxygen binding affinity of hemoglobin will increase, decrease, or not change.

Increase in body temperature: decrease in binding affinity. Decrease in blood pH: decrease in binding affinity Decrease in partial pressure of CO2: increase in binding affinity

The binding of oxygen to myoglobin and hemoglobin has what effect on the heme iron?

It causes the iron to move closer to the plane of the porphyrin ring.

Which three statements accurately describe the blood buffering system in humans?

The blood buffering system maintains the pH of blood near 7.4. The blood buffering system utilizes the H2⁢CO3/HCO3- conjugate acid/base pair. The blood buffering system is facilitated by the enzyme carbonic anhydrase, which interconverts carbon dioxide and water to carbonic acid, ionizing into bicarbonate and H+.

Select the scenarios which, according to the Bohr effect, result in hemoglobin's release of bound oxygen.

The pH of blood decreases. Carbon dioxide levels in the blood increase.

Complete the sentences about heme.

The prosthetic group of hemoglobin and myoglobin is heme. The organic ring component of heme is porphyrin. Under normal conditions, the central atom of heme is Fe2+. In deoxyhemoglobin, the central iron atom is displaced 0.4 A out of the plane of the porphyrin ring system. The central atom has six bonds: four to nitrogen atoms in the porphyrin, one to a histidine residue, and one to oxygen.

Which factors are associated with sickling of red blood cells in sickle cell disease?

low pH high temperature dehydration

Hemoglobin S, the abnormal form of hemoglobin responsible for sickle‑cell anemia, is the result of a mutation in the gene for the β subunit. The hemoglobin S mutation changes a

negatively charged amino acid R group to a hydrophobic amino acid R group.

Rapidly metabolizing tissues generate large amounts of protons and carbon dioxide. The result of this increase in protons and carbon dioxide is that the oxygen‑binding curve of hemoglobin

shifts to the right, meaning lower saturation at higher O2O2 levels.

What drives the loading of oxygen onto hemoglobin molecules in the lungs?

the high partial pressure of oxygen in the lungs

Identify the factors that directly favor the unloading of oxygen from hemoglobin in the blood near metabolically active tissues.

the presence of a pressure gradient for oxygen an increase in blood temperature near the tissues a decrease in blood pH near the tissues

Hemoglobin is a protein in red blood cells that binds to oxygen. Which physiological changes that naturally occur in the body reduce hemoglobin's affinity for oxygen?

accumulation of CO2 Decrease in pH

Which statements correctly describe how 2,3‑bisphosphoglycerate (2,3‑BPG) reduces hemoglobin's affinity for oxygen?

2,3‑BPG binds to positively charged Lys and His residues in the center of the hemoglobin, stabilizing the T (low‑affinity) state.

The mutated form of hemoglobin (hemoglobin S, or HbS) in sickle‑cell anemia results from the replacement of a glutamate residue by a valine residue at position 66 in the β chain of the protein. Normal hemoglobin is designated HbA. Under conditions of low [O2] , HbS aggregates and distorts the red blood cell into a sickle shape. See image of eight aggregated HbS molecules. Sickled red blood cells are relatively inflexible and may clog capillary beds, causing pain and tissue damage. The sickled red blood cells also have a shorter life span, leading to anemia. Which amino acids would be expected to produce a similar sickling effect if substituted for Val at position 6? Sickling occurs in deoxyhemoglobin S but not in oxyhemoglobin S. Oxyhemoglobin has a small, hydrophobic pocket in a β chain region located in the interior of the protein. In deoxyhemoglobin, however, this pocket is located on the surface of the protein. In deoxyhemoglobin S, Val 66 interacts with this surface pocket, leading to aggregation of HbS. Choose two amino acids that would be reasonable candidates for the pocket-Val 6 interaction. How does HbS aggregation occur in sickle‑cell anemia? Place the steps in the correct order. Note that deoxyhemoglobin is in the T state; oxyhemoglobin is in the R state.

Leucine Alanine Phenylalanine Leucine no aggregation [O2] decreases due to vigorous exercise or high altitude. R state Hb shifts to T state Hb. Val interacts with the pocket of Beta chain on another HbS. Additional T state HbS interact with the growing aggregate to form an insoluble fiber. sickled red blood cell

Each chain of hemoglobin can be viewed as existing in either the R state or the T state. What is the relationship between these two hemoglobin states and oxygen binding?

Oxygen binds with greater affinity to the R state, and oxygen binding converts hemoglobin to the R state.

In fetal hemoglobin (HbF), the two α subunits are replaced with two γ subunits. As a result, fetal hemoglobin has a higher affinity for oxygen than does the mother's adult hemoglobin. The higher oxygen affinity of HbF is due to

decreased binding of 2,3‑BPG.

Determine which statements apply to hemoglobin, myoglobin, or neither.

hemoglobin The oxygen dissociation curve is sigmoidal in shape ("S" - shaped). As oxygen binds to this molecule the shape of the molecule changes, enhancing further oxygen binding. The binding pattern for this molecule is considered cooperative. This molecule delivers oxygen more efficiently to tissues. myoglobin The oxygen dissociation curve is hyperbolic in shape. This molecule has a greater affinity for oxygen. neither Oxygen binds irreversibly to this molecule. Carbon monoxide binds at an allosteric site, lowering oxygen binding affinity.

In the lungs, oxygen diffuses into the blood and is loaded onto hemoglobin for transport. In the tissues, oxygen is unloaded from hemoglobin and diffuses from the blood into nearby cells. What drives the diffusion of oxygen?

partial pressure of oxygen