MCAT Biology : Hemoglobin, Blood Cells, and Blood Proteins

Study concepts, example questions & explanations for MCAT Biology

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Example Question #1 : Hemoglobin, Blood Cells, And Blood Proteins

Bilirubin is a byproduct of heme catabolism, and is excreted in the bile and stool. Bilirubin is likely derived from processes in what cell type?

Possible Answers:

Epithelial cells

Adipocytes

Enterocytes

Red blood cells

Correct answer:

Red blood cells

Explanation:

Heme is an important functional group of hemoglobin. Bilirubin, which is a byproduct of heme breakdown, comes from red blood cells. The liver receives unconjugated bilirubin from the blood and conjugates it via phase II metabolism to make it more soluble for excretion via the bile and stool. Fat cells (adipocytes), skin cells (epithelial cells), and small intestine absorptive cells (enterocytes) do not contain heme to be processed into bilirubin.

Example Question #64 : Circulatory System

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?

Possible Answers:

Fetal hemoglobin has a higher affinity for oxygen than adult hemoglobin.

The partial pressure of oxygen in fetal hemoglobin is always the same as that of its mother.

Fetal hemoglobin has a lower affinity for oxygen than adult hemoglobin.

Fetal hemoglobin is composed of four subunits while adult hemoglobin is composed of two.

The partial pressure of oxygen in fetal hemoglobin is always higher than that of its mother.

Correct answer:

Fetal hemoglobin has a higher affinity for oxygen than adult hemoglobin.

Explanation:

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.

Example Question #65 : Circulatory System

Which factors contribute to the Bohr Effect?

Possible Answers:

Low pH, low CO2

Low pH, high CO2, low temperature

Low pH, high CO2

Low pH, high CO2, high temperature

High pH, low CO2

Correct answer:

Low pH, high CO2

Explanation:

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.

Example Question #1 : Hemoglobin, Blood Cells, And Blood Proteins

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.

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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?

Possible Answers:

Cooperativity

Peptide nature

Level of solubility

Iron-binding capacity

Ability to reversibly bind oxygen

Correct answer:

Cooperativity

Explanation:

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.

Example Question #2 : Hemoglobin, Blood Cells, And Blood Proteins

Which of the following gases can be bound by hemoglobin?

Possible Answers:

Carbon monoxide

Oxygen

Carbon dioxide

All of the answers are correct

Correct answer:

All of the answers are correct

Explanation:

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.

Example Question #3 : Hemoglobin, Blood Cells, And Blood Proteins

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

Possible Answers:

High pH

Low temperature

Low levels of carbon dioxide

Low pH

Correct answer:

Low pH

Explanation:

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.

Example Question #1 : Hemoglobin, Blood Cells, And Blood Proteins

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

Possible Answers:

remains the same because only oxygen levels can affect affinity

decreases

increases

remains the same because only carbon dioxide levels can affect affinity

remains the same because only temperature can affect affinity

Correct answer:

decreases

Explanation:

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.

Example Question #4 : 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?

Possible Answers:

An increase in temperature

An increase in carbon dioxide pressure

The partial pressure of oxygen

A decrease in pH

Correct answer:

The partial pressure of oxygen

Explanation:

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 #5 : Hemoglobin, Blood Cells, And Blood Proteins

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 __________.

Possible Answers:

resistance

cooperativity

oxygen shift

coordination

Correct answer:

cooperativity

Explanation:

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 #2 : Hemoglobin, Blood Cells, And Blood Proteins

Which of the following scenarios will cause the oxygen-hemoglobin dissociation curve to shift to the left?

Possible Answers:

Exercise

Fever

Hyperventilation

Decreased pH

Increased 2,3-bisphosphoglycerate

Correct answer:

Hyperventilation

Explanation:

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.

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