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22 Cards in this Set
- Front
- Back
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Bohr effect |
Hemoglobin's decreased affinity for oxygen caused by a lowered pH. |
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Cooperativity |
Structural communication between various subunits of hemoglobin, a result of its quaternary structure. |
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Relaxed state (R state) |
A conformation of hemoglobin when it is bound by oxygen. |
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Tense state (T state) |
A conformation of hemoglobin when it is deoxygenated. |
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What do hemoglobin and myoglobin have in common? Consider both the structure and the function of each protein. |
Each protein has at least one protein subunit, one heme group, and one iron atom. Both proteins bind oxygen reversibly on the iron atom and have similar secondary and tertiary structure. |
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How do myoglobin and hemoglobin differ? Consider both the structure and the function of each protein. |
Hemoglobin has four protein subunits, four heme groups, four iron atoms and can carry up to four oxygen molecules. Hemoglobin undergoes cooperativity and has a sigmoidal oxygen binding curve. Hemoglobin will bind oxygen in the lungs and release oxygen in the tissues. Myoglobin has one protein subunit, one heme group, one iron atom, can bind one oxygen molecule, and has a hyperbolic oxygen binding curve. Myoglobin will carry oxygen from the red blood cells in the capillaries to muscle. |
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What is the role of cooperativity in oxygen binding to hemoglobin? |
Deoxygenated hemoglobin has a low affinity for oxygen compared to myoglobin. Once one oxygen molecule is able to bind to hemoglobin, the protein changes confirmation (shape) and this allows the remaining three oxygen molecules to bind to hemoglobin. Once one oxygen molecule is released from oxygenated hemoglobin, the remaining three oxygen molecules release easily. |
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Why does myoglobin not exhibit cooperativity? |
Myoglobin has only one oxygen molecule, binds oxygen at low oxygen concentrations in the body (myoglobin is half saturated a 2.8 torr), functions to carry oxygen from the red blood cells in the capillaries to the muscle cells. Myoglobin's structure does not have multiple protein subunits, a requirement for cooperativity. |
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What is the relationship between carbon dioxide, pH and hydrogen ion concentration? |
As the amount of carbon dioxide increases, pH decreases and hydrogen ion concentration increases. |
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Identify the image that corresponds to the T (tense) state and R (relaxed) state. |
Oxygenated hemoglobin = R (relaxed) state Deoxygenated = T (tense) state |
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What is the oxygen concentration where hemoglobin will be fully saturated? |
80-100 torr |
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How does this relate to oxygen and hydrogen ion binding and release in hemoglobin? |
As the amount of carbon dioxide decreases from exhalation, H+ decreases and the pH increases. This increase in pH causes hemoglobin to pick up oxygen and release H+. As the amount of carbon dioxide increases from cellular respiration, H+ increases and the pH decreases. The decrease in pH causes hemoglobin to release oxygen and bind H+. |
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How many oxygen molecules are bound to hemoglobin when the protein is in the T-state (tense state)? |
Zero. |
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What is the number of oxygen molecules that must bind in order for hemoglobin to shift to the R-state (relaxed state)? |
One. Hemoglobin's structure changes from T to R-state upon binding one oxygen molecule. |
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Carbon monoxide binds to the __________ in hemoglobin. The binding of carbon monoxide is ________ than the the binding of oxygen in hemoglobin. |
Carbon monoxide binds to the iron atom (held by the heme group) in hemoglobin. The binding of carbon monoxide is stronger than the the binding of oxygen in hemoglobin. |
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Why is the oxygen binding curve in hemoglobin sigmoidal? |
This is due to cooperativity (communication of the four protein subunits). Once one oxygen molecule binds hemoglobin, there is a steep slope in the curve due to the remaining three protein subunits' ability to bind oxygen easily. |
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What direction(s) would you expect the oxygen binding curve to shift when hemoglobin has an increased affinity for oxygen? Why? |
Left and up. At lower oxygen concentrations (x-axis on the graph), hemoglobin is able to bind oxygen and become saturated (y-axis on the graph) more easily. |
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Why is the oxygen binding curve for myoglobin hyperbolic? |
Having only one protein subunit, myoglobin is not capable of undergoing cooperativity (this only exists when a protein has multiple subunits). |
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What conditions cause the Bohr Effect graph (oxygen-binding curve) to shift to the left? What conditions cause the graph to shift to the right? |
A left shift is favored by increase in pH, decrease in H+, and a decrease in 2,3-BPG. A right shift is favored by a decrease in pH, increase in H+, and an increase in 2,3-BPG. |
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What is the shape of the heme group when oxygen is bound to hemoglobin? |
planar |
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Which line on the graph represents hemoglobin's oxygen binding curve at a pH that is lower than 7.4? Why? |
Line A. As pH decreases, hemoglobin is more likely to release oxygen. Hemoglobin has a reduced affinity for oxygen. |
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2,3 BPG binds preferentially to deoxygenated hemoglobin? In doing so, does 2,3 BPG stabilize hemoglobin in the T state or the R state? How does this impact hemoglobin's ability to release oxygen to the tissues? |
T state Hemoglobin releases oxygen to the tissues as the T-state has a reduced affinity for binding oxygen. |
