MCAT Biology : Antibodies and Antigens

Study concepts, example questions & explanations for MCAT Biology

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Example Questions

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Example Question #79 : Immune System

A patient requiring a blood transfusion is discovered to have type AB- negative blood. Which donor blood types can they accept?

Possible Answers:

All blood types; AB- is the universal receiver. 

B-, A-, AB-, and O-

Type AB- only

A+, B+, AB+, and O+

Correct answer:

B-, A-, AB-, and O-

Explanation:

In blood typing, the concern is avoiding the administration a blood transfusion that will be attacked by the body's immune system. For each antigen not present on the recipient's blood cells, there will be an antibody present in their blood stream. Therefore, someone who has type A blood will have an "anti-B" antibody. A transfusion of blood presenting the B antigen would be attacked and rejected by the type A individual's body. The Rh group (+/-) works similarly. Those who are Rh negative will have an antibody present to attack blood cells with the Rh group. Similarly, if someone is is Rh positive, there will be no Rh antibodies in his or her body and he or she could accept either Rh- or Rh+ blood. The patient in this question has type AB- blood, so he or she has no antibodies except for those that bind to Rh-positive blood. Therefore, all Rh-negative blood types are acceptable. (Type O blood signifies that the blood cells have no antigens present.)

Example Question #73 : Immune System

There are a large variety of over-the-counter pregnancy tests, although all of them share a set of common principles.

These home pregnancy tests are immunoassays which detect the presence of the peptide hormone human chorionic gonadotropin (hCG). hCG is produced by the fertilized ovum and released into the mother's bloodstream, preventing the degradation of the corpus luteum and thereby preventing menstruation. By the time of the mother's first missed period, hCG levels in the urine are high enough to detect.

The home pregnancy test generally involves dipping a stick containing immobilized hCG monoclonal antibodies into a urine sample. If hCG is present in the urine, it will bind to the monoclonal antibodies on the dipstick. The dipstick is then placed in a solution containing a second monoclonal antibody which recognizes the bound hCG antibody complex on the surface of the dipstick. This second antibody is conjugated to colloidal gold particles which change color when they are immobilized, indicating a positive test result (i.e., pregnancy).

The monoclonal antibodies used in the home pregnancy test __________.

Possible Answers:

come from several different T-cell clones and bind to multiple antigen sites on the hCG molecule

come from a single T-cell clone and bind to multiple antigen sites on the hCG molecule

come from a single B-cell clone and bind to multiple antigen sites on the hCG molecule

come from a single T-cell clone and bind to a single antigen site on the hCG molecule

come from a single B-cell clone and bind to a single antigen site on the hCG molecule

Correct answer:

come from a single B-cell clone and bind to a single antigen site on the hCG molecule

Explanation:

Antibodies are made by B-cells, not T-cells. Monoclonal antibodies, as their name implies, are produced by a single clone of B-cells. In other words, a single B-cell is provoked to divide, producing a clone of identical cells. These cells then crank out one single type of antibody. These are monoclonal antibodies. Monoclonal antibodies only strongly recognize and bind to one specific antigenic site. The hCG molecule, being a polypeptide, may have multiple antigenic sites that can be recognized by antibodies, but a given set of monoclonal antibodies only recognizes one of these sites.

Example Question #431 : Biology

Which immunoglobulin is the predominant subclass that can cross the placenta?

Possible Answers:

IgA

IgD

IgG

IgM

IgE

Correct answer:

IgG

Explanation:

IgG (exists as a monomer in the blood) and IgE are both small enough to cross the placenta however, IgE is present in very low levels in the plasma.

Example Question #82 : Immune System

Allergies are conditions caused by hypersensitivity by the immune response and typically develop upon first encounter with the foreign antigen. The onset of the allergic response is typically fast and acute. Symptoms include shortness of breath, runny nose, red eyes, swelling, etc. Mast cells are found in skin, mucosal tissue and the gastrointestinal tract and play a significant role in the inflammatory response and in immediate allergic reactions.  

Upon exposure to allergen bound by antibody, mast cells are able to release potent inflammatory mediators, such as histamine, proteases, chemotactic factors, and cytokines act on the vasculature, smooth muscle, mucous glands and inflammatory cells. Which antibody subclass is bound to the allergens and responsible for activating mast cells?

Possible Answers:

IgD

IgA

IgG

IgM

IgE

Correct answer:

IgE

Explanation:

IgE is the subclass of immunoglobulins that plays a critical role in the allergy response. IgE binds to allergens which in turn bind to Fc receptors on the mast cells, triggering the release of numerous inflammatory mediators, including histamine.

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