MCAT Biology : Biology
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Example Question #7 : Hemoglobin, Blood Cells, And Blood Proteins
Hemoglobin is the protein responsible for the transport of oxygen throughout the bloodstream. The saturation of hemoglobin can be graphed based on the pressure of oxygen. As the pressure of oxygen increases, the saturation of hemoglobin with oxygen will increase in a sigmoidal fashion. This oxygen dissociation curve can be shifted depending on the external conditions in the blood.
Which of the following factors will not decrease the dissociation curve between oxygen and hemoglobin?
A decrease in pH
The partial pressure of oxygen
An increase in carbon dioxide pressure
An increase in temperature
The partial pressure of oxygen
The oxygen dissociation curve is a graph of hemoglobin saturation versus oxygen partial pressure. As oxygen partial pressure increases, hemoglobin will generally be more saturated. The oxygen partial pressure will affect the saturation percentage of hemoglobin in the blood, but will not shift the curve itself. All other options will shift the oxygen dissociation curve to the right, lowering hemoglobin's affinity for oxygen.
Example Question #106 : Circulatory And Respiratory Systems
Hemoglobin displays a property whereby binding of one oxygen molecule decreases the resistance of the hemoglobin molecule to additional oxygen binding. This property of hemoglobin is known as __________.
coordination
oxygen shift
resistance
cooperativity
cooperativity
Hemoglobin displays the unique property of cooperativity, meaning that once one molecule of oxygen has bound to the hemoglobin molecule, adding the three next molecules is easier. This gives the hemoglobin binding curve the typical sigmoidal oxygen dissociation curve.
Cooperativity helps hemoglobin bind four oxygen molecules in the lungs and maintain the bonds until it enters a region of very low oxygen partial pressure. The most energy is required to remove the first oxygen; the next three are easier because the cooperativity has been lessened. As hemoglobin travels, it is able to selectively distribute oxygen the areas of the body that need it most because of this property.
Example Question #107 : Circulatory And Respiratory Systems
Which of the following scenarios will cause the oxygen-hemoglobin dissociation curve to shift to the left?
Hyperventilation
Increased 2,3-bisphosphoglycerate
Exercise
Decreased pH
Fever
Hyperventilation
Hemoglobin's affinity for oxygen can vary based upon the environment. A right shift, which lowers hemoglobin's affinity for oxygen, occurs when there is a need for oxygen to be released to surrounding tissue. This occurs during exercise, increased temperatures, increased 2,3-bisphosphglycerate, increased carbon dioxide, and decreased pH.
Hyperventilation will increase oxygen and decrease carbon dioxide, which will effectively cause a left shift. Left shifts occur under circumstances opposite from the right shift. A decrease in temperature, 2,3-bisphosphoglycerate, or carbon dioxide will cause a left shift.
Example Question #901 : Biology
Which of the following changes in blood properties would not decrease the affinity of hemoglobin for oxygen?
Increased blood 2,3-bisphosphoglycerate
Increased temperature
Decreased partial pressure of carbon dioxide
Decreased blood pH
Decreased partial pressure of carbon dioxide
Several factors are capable for shifting the oxygen dissociation curve. A decrease in pH or an increase in carbon dioxide partial pressure indicates a need to remove carbon dioxide wastes from the system. Hemoglobin affinity for oxygen will decrease under these conditions in order to accommodate the carbon dioxide for removal. Decreased carbon dioxide partial pressure will increase the affinity for oxygen rather than decrease it.
Increased temperature and increased 2,3-bisphosphoglycerate will also decrease the hemoglobin affinity for oxygen.
A decrease in binding affinity shifts the oxygen dissociation curve to the right, while an increase shifts the curve to the left.
Example Question #902 : Biology
Hemoglobin is the principal oxygen-carrying protein in humans. It exists within erythrocytes, and binds up to four diatomic oxygen molecules simultaneously. Hemoglobin functions to maximize oxygen delivery to tissues, while simultaneously maximizing oxygen absorption in the lungs. Hemoglobin thus has a fundamentally contradictory set of goals. It must at once be optimized to absorb oxygen, and to offload oxygen. Natural selection has overcome this apparent contradiction by making hemoglobin exquisitely sensitive to conditions in its microenvironment.
One way in which hemoglobin accomplishes its goals is through the phenomenon of cooperativity. Cooperativity refers to the ability of hemoglobin to change its oxygen binding behavior as a function of how many other oxygen atoms are bound to the molecule.
Fetal hemoglobin shows a similar pattern of cooperativity, but has unique binding characteristics relative to adult hemoglobin. Fetal hemoglobin reaches higher saturation at lower oxygen partial pressure.
Because of cooperativity, adult and fetal oxygen-hemoglobin dissociation curves appear as follows.
Beyond its ability to carry oxygen, hemoglobin is also effective as a blood buffer. The general reaction for the blood buffer system of hemoglobin is given below.
H+ + HbO2 ←→ H+Hb + O2
Based on the above graph, which of the following would be expected when oxygen unloads from hemoglobin?
The remaining oxygen atoms bind with the same affinity
Hemoglobin changes conformation only when the last oxygen is unloaded
The remaining oxygen atoms bind with lower affinity
The remaining oxygen atoms bind with higher affinity
Hemoglobin does not change conformation
The remaining oxygen atoms bind with lower affinity
The basic idea of cooperativity is that oxygen will bind with lower affinity once an oxygen atom is removed. Once you remove the first oxygen atom, the remaining ones are more likely to come off to supply tissue. This change is instigated by conformational changes in hemoglobin structure when an oxygen is removed.
Example Question #903 : Biology
Fetal circulation differs greatly from that of adults. For example, a fetus does not actually have functional lungs until birth, and instead receives oxygen from the mother umbilical vein. Which is not an adaptation of the fetal circulatory system?
The ductus arteriosus
The foramen ovale
The ductus venosus
Fetal hemoglobin has a comparatively high affinity for oxygen
Fetal myoglobin has a comparatively low affinity for oxygen
Fetal myoglobin has a comparatively low affinity for oxygen
Most adaptations of the fetal circulatory system are designed to bypass the lungs and liver, which develop especially slowly. The ductus venosus shuttles blood directly from the umbilical vein to the inferior vena cava, avoiding the liver entirely. The foramen ovale is a right-to-left shunt between the atria that sends blood away from the right ventricle; the ductus arteriosus shunts the remaining blood from the right ventricle to the aorta to bypass the lungs. Finally, fetal hemoglobin has a high affinity for oxygen because it must compete with maternal blood in the placenta.
Fetal myoglobin does not have a low affinity for oxygen.
Example Question #901 : Biology
Hemoglobin is the principal oxygen-carrying protein in humans. It exists within erythrocytes, and binds up to four diatomic oxygen molecules simultaneously. Hemoglobin functions to maximize oxygen delivery to tissues, while simultaneously maximizing oxygen absorption in the lungs. Hemoglobin thus has a fundamentally contradictory set of goals. It must at once be opitimized to absorb oxygen, and to offload oxygen. Natural selection has overcome this apparent contradiction by making hemoglobin exquisitely sensitive to conditions in its microenvironment.
One way in which hemoglobin accomplishes its goals is through the phenomenon of cooperativity. Cooperativity refers to the ability of hemoglobin to change its oxygen binding behavior as a function of how many other oxygen atoms are bound to the molecule.
Fetal hemoglobin shows a similar pattern of cooperativity, but has unique binding characteristics relative to adult hemoglobin. Fetal hemoglobin reaches higher saturation at lower oxygen partial pressure.
Because of cooperativity, adult and fetal oxygen-hemoglobin dissociation curves appear as follows.
Beyond its ability to carry oxygen, hemoglobin is also effective as a blood buffer. The general reaction for the blood buffer system of hemoglobin is given below.
H+ + HbO2 ←→ H+Hb + O2
While most of the oxygen transported in blood is bound to hemoglobin, only a small fraction of carbon dioxide (CO2) present in blood is transported via this carrier. Most is dissolved in blood in an alternative form. Why does CO2 need to be changed to an alternative form to dissolve into blood?
CO2 is polar, and needs to be modified to bind to carrier proteins like albumin
CO2 is nonpolar, and blood is not an aqueous solution
CO2 is polar, and blood is an aqueous solution
CO2 is polar, and blood is not an aqueous solution
CO2 is nonpolar, and blood is an aqueous solution
CO2 is nonpolar, and blood is an aqueous solution
Carbon dioxide (CO2) is nonpolar, and thus can dissolve well only in nonpolar solvents. Since blood is an aqueous (and polar) solvent, CO2 needs to be converted to a polar form via blood enzymes to allow it to be dissolved directly in water.
Example Question #904 : Biology
Which of the following gases can bind to hemoglobin?
Carbon dioxide (CO2)
Hemoglobin can bind to all of these gases
Oxygen (O2)
Carbon monoxide (CO)
Hemoglobin can bind to all of these gases
Hemoglobin can bind to all three of these gases, however, it binds to each of them with a different affinity. Hemoglobin's affinity for the three gases, from highest to lowest, is listed below.
carbon monoxide (CO) > oxygen (O2) > carbon dioxide (CO2).
Note that cabron monoxide has the highest affininty; this is why is can be dangerous to inhale too much carbon monoxide, as it will displace onxygen that would otherwise bind to hemoglobin.
Example Question #905 : Biology
Carbonic anhydrase serves to convert carbon dioxide wastes, produced from cellular respiration, into bicarbonate. This bicarbonate buffers blood pH and allows for the transport of more carbon dioxide equivalents in the blood to the kidneys for excretion. The reaction catalyzed by carbonic anhydrase is:
How would running, as compared to walking, change the pH of the blood if breathing rate remains constant?
Decreased blood pH
Increased blood pH
The change cannot be determined without knowing more about the runner
Blood pH will remain the same
Decreased blood pH
Cellular respiration is more active during running than during walking, producing more carbon dioxide. The carbon dioxide will enter the carbonic anhydrase reaction, producing more protons in the blood and lowering the pH. To counter this drop in pH, runners will naturally increase their breathing rate. This serves to deliver more oxygen to the muscles, as well as to remove more carbon dioxide wastes and prevent acid from building in the blood.
Example Question #904 : Biology
Hemoglobin is the principal oxygen-carrying protein in humans. It exists within erythrocytes, and binds up to four diatomic oxygen molecules simultaneously. Hemoglobin functions to maximize oxygen delivery to tissues, while simultaneously maximizing oxygen absorption in the lungs. Hemoglobin thus has a fundamentally contradictory set of goals. It must at once be optimized to absorb oxygen, and to offload oxygen. Natural selection has overcome this apparent contradiction by making hemoglobin exquisitely sensitive to conditions in its microenvironment.
One way in which hemoglobin accomplishes its goals is through the phenomenon of cooperativity. Cooperativity refers to the ability of hemoglobin to change its oxygen binding behavior as a function of how many other oxygen atoms are bound to the molecule.
Fetal hemoglobin shows a similar pattern of cooperativity, but has unique binding characteristics relative to adult hemoglobin. Fetal hemoglobin reaches higher saturation at lower oxygen partial pressure.
Because of cooperativity, adult and fetal oxygen-hemoglobin dissociation curves appear as follows.
Beyond its ability to carry oxygen, hemoglobin is also effective as a blood buffer. The general reaction for the blood buffer system of hemoglobin is given below.
H+ + HbO2 ←→ H+Hb + O2
Considering the described oxygen affinity pattern for hemoglobin, which curve is likely to depict fetal hemoglobin?
Curve 1, as it shows less affinity for oxygen
Curve 2, as it shows greater affinity for oxygen
Cannot be determined from the information given
Curve 1, as it shows greater affinity for oxygen
Curve 2, as it shows less affinity for oxygen
Curve 1, as it shows greater affinity for oxygen
Curve 1 shows greater affinity for oxygen than curve 2, as it is higher up the y-axis at any single point on the x-axis. We would expect this finding for fetal hemoglobin, which would need to extract oxygen from maternal blood.
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