Hemoglobin, Blood Cells, and Blood Proteins
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MCAT Biology › Hemoglobin, Blood Cells, and Blood Proteins
Which of the following gases can bind to hemoglobin?
Hemoglobin can bind to all of these gases
Oxygen (O2)
Carbon dioxide (CO2)
Carbon monoxide (CO)
Explanation
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.
Which factors contribute to the Bohr Effect?
Low pH, high CO2
High pH, low CO2
Low pH, high CO2, high temperature
Low pH, low CO2
Low pH, high CO2, low temperature
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.
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?
The plasma layer
The buffy coat layer
The red blood cell layer
The leukocyte layer
Explanation
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.
Which of the following cell types does not possess a nucleus in its mature form?
Erythrocytes
Granulocytes
Neurons
Adipocytes
Explanation
Erythrocytes are chiefly responsible for delivering oxygen to cells throughout the body and do not possess nuclei in their mature form. The absence of a nucleus and mitochondria from mature erythrocytes prevents transported oxygen from being consumed by the carrier cell, instead of being delivered to the body.
Granulocytes are a division of white blood cells and frequently have lobed or multiple nuclei. Neurons contain nuclei in their somas and adipocytes contain peripheral nuclei, located close to the membrane.
An individual with hemophilia, most likely has a deficiency in which of the following proteins?
Fibrinogen
Renin
Vasopressin
Albumin
Major histocompatibility complex proteins
Explanation
Fibrinogen is converted to fibrin by the action of thrombin, and fibrin is the protein that actually forms a blood clot. An inability to properly form clots, such as is seen in hemophilia, could arise from a defect in fibrinogen, resulting in a problem with the clotting pathway.
Renin is an enzyme released by the kidney, which creates angiotensin to help raise blood pressure. Vasopressin is a posterior pituitary hormone that acts on the kidney to retain water. Albumin is a plasma protein that functions to maintain the oncotic pressure in the blood, as well as to transport fatty acids. Major histocompatibility complex (MHC) proteins are used to present antigens to the immune system.
Which of the following scenarios will cause the oxygen-hemoglobin dissociation curve to shift to the left?
Hyperventilation
Exercise
Fever
Increased 2,3-bisphosphoglycerate
Decreased pH
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.
Which statement regarding blood typing is correct?
A person with B- blood can donate to a person whose blood type is AB+.
A woman with Rh- blood is at risk for developing erythroblastosis fetalis during her first pregnancy if the fetus is Rh+.
A person with AB- blood can donate to a person whose blood type is O-.
A person with O- blood can receive a blood donation from someone with O+ blood.
The presence of the Rh factor is coded for by a recessive allele.
Explanation
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.
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 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?
They lack a nucleus
They lack a cell membrane
They are larger than all other cells
They are produced in the thymus
They contain protein support for their membranes
Explanation
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.
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?
Red blood cells
Adipocytes
Epithelial cells
Enterocytes
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.
Carbonic anhydrase is a very important enzyme that is utilized by the body. The enzyme catalyzes the following reaction:
A class of drugs that inhibits this enzyme is carbonic anhydrase inhibitors (eg. acetazolamide, brinzolamide, dorzolamide). These drugs are commonly prescribed in patients with glaucoma, hypertension, heart failure, high altitude sickness and for the treatment of basic drugs overdose.
In patients with hypertension, carbonic anhydrase inhibitors will prevent the reabsorption of sodium chloride 
When mountain climbing, the atmospheric pressure is lowered as the altitude increases. As a result of less oxygen into the lungs, ventilation increases. From the equation above, hyperventilation will result in more 
Carbonic anhydrase inhibitors are useful in patients with a drug overdose that is acidic. The lumen of the collecting tubule is nonpolar. Due to the lumen's characteristic, molecules that are also nonpolar and uncharged are able to cross the membrane and re-enter the circulatory system. Since carbonic anhydrase inhibitors alkalize the urine, acidic molecules stay in a charged state.
How will excess intake of a carbonic anhydrase inhibitor affect the hemoglobin dissociation curve?
Shifts to the right
Shifts down
Shifts to the left
No change
Shifts up
Explanation
Carbonic anhydrase inhibitors will decrease the blood's pH. Conditions that will shift the hemoglobin dissociation curve to the right are increased temperature, increased 2,3-DPG, and decreased pH.