Hemoglobin, Blood Cells, and Blood Proteins - MCAT Biology

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Question

A scientist takes a group of erythrocytes (red blood cells) and places them in a beaker containing a solution. The cells begin to shrink and eventually lyse. What can be concluded about the solution?

Answer

Placing erythrocytes in a hypertonic solution would cause them to shrink and burst, becuase water from the erythrocytes would move from high to low concenration (inside the cells to the outside hypertonic environment). Albumin and bicarbonate would have no effect, because they are normal components of blood. Placing them in a hypotonic solution would cause them to swell up.

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Question

A fetus does not breathe inside the womb, and so it must obtain oxygen a different way. What property of hemoglobin allows a fetus to recieve the oxyge it needs to develop?

Answer

Fetal hemoglobin has a higher affinity for oxygen that adult hemoglobin. Maternal and Fetal blood never mix during pregnancy, but they come close to each other in the placenta. Oxygen diffuses easily to fetal hemoglobin here. The reason fetal hemoglobin has a higher affinity is it is composed of two alpha and two gamma subunits, while adult hemoglobin is composed of two alpha and two beta subunits.

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Question

Which of the following is a cause of alkalosis?

Answer

Hyperventilation is a classic example of a process that can cause alkalosis, or basicity of the bloodstream. Hyperventilation can cause a net loss of CO2. Low levels of CO2 can cause respiratory alkalosis via reduction of carbonate in the blood. Lactate—also known as lactic acid—is a product of anaerobic respiration, and decreases blood pH. Increased levels of urea and creatinine indicate renal acidosis, a form of metabolic acidosis, which occurs when the kidney does not remove enough acid from the body.

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Question

What could the blood pH of a person who has blood acidosis (more acidic blood than normal) possibly be?

Answer

The normal pH of blood is around 7.3, which means blood is normally slightly basic. A truly neutral pH is 7.0. Whenever the pH of blood is under 7.3 (not 7.0) it is considered acidosis, and so our answer is either 7.2 or 6.8.

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Question

Which factors contribute to the Bohr Effect?

Answer

The Bohr Effect describes hemoglobin's affinty for oxygen as a function of blood pH and carbon dioxide content. An increase in CO2 concentration will lower the blood pH, causing the hemoglobin affinity for oxygen to reduce. High temperature also causes oxygen to be released from hemoglobin, but is not related to the Bohr Effect.

Think about when you're exercising. Your blood has a reduced O2 concentration and an elevated CO2 concentration. These factors allow hemoglobin to release more oxygen in the muscles to faciliate ATP production and maintain energy levels.

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Question

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.

Untitled

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?

Answer

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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Question

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.

Untitled

Beyond its ability to carry oxygen, hemoglobin is also effective as a blood buffer. The general reaction for the blood buffer system of hemoglobin given below.

H+ + HbO2 ←→ H+Hb + O2

Hemoglobin is the most important component of red blood cells. How are red blood cells different from other cells of the body?

Answer

Red blood cells are unique in that they lack a nucleus and are functionally just "bags of hemoglobin." They are among the most specialized cells, doing little else but transporting oxygen in the blood.

The choice indicating protein support for the membrane may have also been tempting, and is true. This characteristic, however, is shared by other cells of the body. Also remember that red blood cells are produced by red bone marrow (and sometimes the liver), while certain white blood cells mature in the thymus.

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Question

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.

Untitled

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?

Answer

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.

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Question

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.

Untitled

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

Myoglobin is a similar carrier molecule to hemoglobin, but it only has one site of oxygen binding instead of four. Which characteristic of hemoglobin is most likely not shared by myoglobin?

Answer

Cooperativity, as defined in the passage, requires more than one binding site. Without more than one binding site, it is impossible for a carrier to change its affinity for additional cargo after the first piece is either loaded or unloaded. That additional cargo simply doesn't exist for myoglobin.

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Question

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.

Untitled

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?

Answer

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.

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Question

Which statement regarding blood typing is correct?

Answer

The AB+ blood type is known as the "universal recipient" type, therefore, people with any blood type can donate to an AB+ individual.

As for the incorrect answers, a person with O- blood has the "universal donor" type, and can only receive blood from other O- individuals. Erythroblastosis fetalis, also known as hemolytic disease of the newborn, cannot occur during a woman's first pregnancy because her body has not yet produced anti-Rh antibodies. Finally, Rh factor presence is a genetically dominant condition.

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Question

Which of the following gases can be bound by hemoglobin?

Answer

All of these gases can be bound by hemoglobin. Hemoglobin transports oxygen from the lungs to the necessary tissue, and carbon dioxide from the tissue to the lungs. Hemoglobin has a much higher affinity for carbon monoxide than oxygen, which is why it is so dangerous to inhale carbon monoxide.

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Question

Which of the following accurately represents the entire composition of blood?

Answer

Human blood contains 55% plasma and 45% cells. The cells include erythrocytes (red blood cells), leukocytes (white blood cells), and thrombocytes (platelets). Plasma is largely composed of water, protein (albumin), and clotting factors.

Note that blood serum is simply blood plasma with the clotting factor elements (fibrinogen) removed.

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Question

Which of the following most accurately depicts the process of clotting?

Answer

Thromboplastin is released when damage occurs to a tissue. Prothrombin and fibrinogen are both present in the blood. When thromboplastin interacts with the blood, it converts prothrombin to its active state, thrombin. Thrombin then cleaves fibrinogen, converting it to its active state, fibrin. Fibrin is exceptional at forming cross-linked mesh-like interactions, and in doing so traps passing blood cells and plasma proteins. This blockage and accumulation of blood elements becomes the clot.

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Question

Which of the following gases can bind to hemoglobin?

Answer

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.

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Question

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?

Answer

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.

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Question

Which of the following is most likely to decrease oxygen's affinity to hemoglobin in the bloodstream?

Answer

High levels of carbon dioxide (CO2), low pH, and high temperatures all act to decrease oxygen's affinity toward human hemoglobin. Think of working muscle, which produces hot, acidic, high CO2 conditions in the blood; in this environment, it is important for hemoglobin to release transported oxygen to provide an aerobic environment to the muscle.

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Question

If an individual's blood has a slightly lower pH than normal, this means that oxygen affinity to hemoglobin __________.

Answer

A decrease in pH is generally caused by an increase in carbon dioxide in the blood, and will cause hemoglobin to have a lower affinity to oxygen. This makes sense, because we want to easily release oxygen to tissues with high levels of carbon dioxide, and quickly bind and remove the carbon dioxide from the cells to the lungs for expiration from the body.

Increased temperature will also decrease the affinity of hemoglobin for oxygen.

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Question

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?

Answer

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.

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Question

Albumin is created in the liver and is an important protein found in the blood. If a vial of blood is centrifuged, in which of the following layers would albumin be found?

Answer

When centrifuged, blood will divide into three parts: the plasma layer, the buffy coat layer, and the red blood cell layer. The plasma layer contains albumin, immunoglobulins, and blood clotting factors. The buffy coat is composed of leukocytes, and the red blood cell layer is composed of erythrocytes.

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