MCAT Biology : Antibodies and Antigens

Study concepts, example questions & explanations for MCAT Biology

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Example Questions

Example Question #11 : Antibodies And Antigens

Major histocompatibility complex (MHC) II molecules are responsible for displaying antigens from what invading pathogen?

Possible Answers:

Bacteria

Viruses

Parasites

Fungi

Correct answer:

Bacteria

Explanation:

The "self" antigens that prevent T-cells from attacking the body are called MHC molecules. These molecules come in two classes: class I and class II. RNA, DNA, and proteins from bacteria are displayed after the bacterium is ingested by an antigen-presenting cell using MHC class II molecules. The antigen-presenting cell reports the MHC molecule corresponding to the bacteria to a helper T-cells. Once the helper T-cells see this unrecognized part of the bacterium, and detect it as different from "self," they can initiate the adaptive immune response.

Example Question #11 : Antibodies And Antigens

Blood types are designated A, B, AB, and O depending on the glycoprotein presented on the surface of the red blood cells. If a person has glycoproteins  and . What is the person's blood type?

Possible Answers:

B

AB

O

A

Correct answer:

A

Explanation:

The glycoproteins , and  are responsible for the A, B, and O blood types in humans, respectively.

 and  are dominant to , meaning that blood types A and B are dominant to O. Additionally,  and  can be co-dominant, giving the AB blood type. The person in the question has  and  glycoproteins, giving the patient the A blood type, as  is dominant to . Genotypically, they will carry alleles for both A and O blood type, but their phenotype will be only A.

Example Question #71 : Immune System

Hypersensitivity reactions occur when body tissues are affected by an abnormal immune reaction. The result is damage to normal tissues and clinical illness. A peanut allergy is an example of a hypersensitivity reaction, but there are three additional broad classes.

One class involves the abnormal production or deposition of antibodies. Antibodies are B-cell derived molecules that normally adhere to pathogens, rendering them unable to continue an infection. When antibodies are produced against normal tissues, however, disease can result. Figure 1 depicts a schematic structure of an antibody.

Antibodies can be divided into two peptide chains: heavy and light. Heavy chains form the backbone of the antibody, and are attached to light chains via covalent bonding. Each heavy and light chain is then further divided into constant and variable regions. Variable regions exhibit molecular variety, generating a unique chemical identity for each antibody. These unique patterns help guarantee that the body can produce antibodies to recognize many possible molecular patterns on invading pathogens.

 

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Before antibodies enter into circulation, they exist as B-cell receptors (BCRs). BCRs are transmembrane proteins that are identical to the antibodies that exist in free circulation, with the exception of one component. Which component is likely present in BCRs, but not in antibodies in solution with blood?

Possible Answers:

A span of charged amino acids

A span of basic amino acids

A span of hydrophobic amino acids

A span of acidic amino acids

A span of hydrophilic amino acids

Correct answer:

A span of hydrophobic amino acids

Explanation:

A B-cell receptor (BCR) is a transmembrane protein, and thus must have an integral membrane domain consisting of hydrophobic amino acids. This is different from antibodies in solution, which would likely not have such an integral membrane domain. The mature antibody must be capable of being in the aqueous blood solution. The persistence of a hydrophobic region in the antibody would inhibit its solubility in the blood, reducing its functionality.

Example Question #71 : Immune System

Hypersensitivity reactions occur when body tissues are affected by an abnormal immune reaction. The result is damage to normal tissues and clinical illness. A peanut allergy is an example of a hypersensitivity reaction, but there are three additional broad classes.

One class involves the abnormal production or deposition of antibodies. Antibodies are B-cell derived molecules that normally adhere to pathogens, rendering them unable to continue an infection. When antibodies are produced against normal tissues, however, disease can result. Figure 1 depicts a schematic structure of an antibody.

Antibodies can be divided into two peptide chains: heavy and light. Heavy chains form the backbone of the antibody, and are attached to light chains via covalent bonding. Each heavy and light chain is then further divided into constant and variable regions. Variable regions exhibit molecular variety, generating a unique chemical identity for each antibody. These unique patterns help guarantee that the body can produce antibodies to recognize many possible molecular patterns on invading pathogens.

 

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A patient presents to their local primary care clinic with a 1-day old influenza infection. Their blood is drawn and analyzed for antibodies. Four months after the infection, their physician draws their blood again and studies the presence of antibodies. Which of the following is most likely to be true?

Possible Answers:

Antibodies do not form in response to viral infections such as influenza

There will be more anti-influenza antibodies at the four month blood draw

There will be fewer anti-influenza antibodies at the four month blood draw

We cannot predict the changes in the amount of antibodies at the four month blood draw relative to the initial draw

There will be an equal number of anti-influenza antibodies at the four month blood draw and the initial draw

Correct answer:

There will be more anti-influenza antibodies at the four month blood draw

Explanation:

Antibodies are part of the adaptive immune response. As a result, we would expect that their concentration during an acute infection would be lower than their concentration in a post-infection (convalescent) serum sample. In fact, many diagnostic assays use this phenomenon to confirm diagnoses.

Antibodies are among the major immune responses to viral infections, especially influenza.

Example Question #12 : Antibodies And Antigens

Hypersensitivity reactions occur when body tissues are affected by an abnormal immune reaction. The result is damage to normal tissues and clinical illness. A peanut allergy is an example of a hypersensitivity reaction, but there are three additional broad classes.

One class involves the abnormal production or deposition of antibodies. Antibodies are B-cell derived molecules that normally adhere to pathogens, rendering them unable to continue an infection. When antibodies are produced against normal tissues, however, disease can result. Figure 1 depicts a schematic structure of an antibody.

Antibodies can be divided into two peptide chains: heavy and light. Heavy chains form the backbone of the antibody, and are attached to light chains via covalent bonding. Each heavy and light chain is then further divided into constant and variable regions. Variable regions exhibit molecular variety, generating a unique chemical identity for each antibody. These unique patterns help guarantee that the body can produce antibodies to recognize many possible molecular patterns on invading pathogens.

 

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The readily reversible interactions between antigens and antibodies most probably use which of the following interactions?

I. Hydrogen bonding

II. Dipole-dipole interactions

III. Nonpolar covalent

Possible Answers:

I only

I, II, and III

I and III

III only

I and II

Correct answer:

I and II

Explanation:

The interaction between pathogens and antibodies are non-covalent, and are comprised of weak intermolecular interactions. This question specifies that these interactions are reversible, which immediately eliminates covalent bonds as an option. Covalent bonding results in strong, long-term interaction on the atomic level. Dipole-dipole interactions and hydrogen bonding are more loose associations between full molecules, and can easily be broken in order for the molecules to dissociate.

Example Question #11 : Antibodies And Antigens

The receptor on the surface of a B-lymphocyte is a membrane-bound antibody. Which of the following is not a function of an antibody?

Possible Answers:

Tagging pathogens

Enhancing phagocytic ability of macrophages

Binding antigens

Removing pathogens

Correct answer:

Removing pathogens

Explanation:

Antibodies are not responsible for the removal of pathogens, only the binding and/or tagging foreign materials for destruction by other immune cells. Antibodies are released into the blood stream and bind to matching antigens on the surface of infectious cells. By binding and tagging foreign materials, antibodies enhance the ability of other immune cells (such as macrophages) to engulf or phagocytose the foreign material, leading to its destruction and removal.

Antibodies themselves cannot remove pathogens; they only aid in the removal of pathogens by immune cells.

Example Question #11 : Antibodies And Antigens

Type 1 diabetes is a well-understood autoimmune disease. Autoimmune diseases result from an immune system-mediated attack on one’s own body tissues. In normal development, an organ called the thymus introduces immune cells to the body’s normal proteins. This process is called negative selection, as those immune cells that recognize normal proteins are deleted. If cells evade this process, those that recognize normal proteins enter into circulation, where they can attack body tissues. The thymus is also important for activating T-cells that recognize foreign proteins.

As the figure below shows, immune cells typically originate in the bone marrow.  Some immune cells, called T-cells, then go to the thymus for negative selection. Those that survive negative selection, enter into general circulation to fight infection. Other cells, called B-cells, directly enter general circulation from the bone marrow. It is a breakdown in this carefully orchestrated process that leads to autoimmune disease, such as type 1 diabetes.

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A doctor discovers that a newborn baby has a rare infection of her lungs. He does an analysis of the baby's blood and finds a near-total lack of antibodies in the plasma. The remainder of her immune system is intact. In which of the numbered arrows of the given figure is there most likely to be a breakdown in normal functioning?

Possible Answers:

2 and 3

1 and 2

1, only

3, only

2, only

Correct answer:

2, only

Explanation:

The lack of antibodies indicates a failure of B-cell maturation, as B-cells are the only cells to produce antibodies. B-cells, as the passage indicates, are sent from the bone marrow directly into the circulation via arrow 2; thus, a breakdown in this process would be expected to lead to a loss of antibodies in the blood. Because the question states that the rest of the immune system is intact, we can assume that T-cell maturation is unaffected in the patient, meaning that arrows 1 and 3 are not affected.

Example Question #11 : Antibodies And Antigens

Which of the following statements is false concerning the humoral immune system?

Possible Answers:

Memory B-cells are used to create antibodies for new antigens

A plasma cell creates only one specific antibody

An antibody is used to recognize only one antigen

Dendritic cells present antigens to lymphocytes

B-lymphocytes can differentiate into plasma cells

Correct answer:

Memory B-cells are used to create antibodies for new antigens

Explanation:

Memory B-cells proliferate and remain in the body for great periods of time following an infection. These cells are used to respond to infections that have been previously seen by the immune system. They create antibodies for a specific antigen previously seen by the body.

All other answers are true statements. Each antibody responds to only a single antigen, and each plasma cell synthesizes only one type of antibody. B-cells differentiate into plasma cells when presented with a new antigen. Dendritic cells often act to present such antigens to T-cells and B-cells.

Example Question #71 : Immune System

What component of the adaptive immune system binds to antibodies and allows for holes to be placed into bacterial cell membranes?

Possible Answers:

Major histocompatibility complex (MHC) I

Complement

Major histocompatibility complex (MHC) II

Antigens

Correct answer:

Complement

Explanation:

Once antibodies, produced by plasma cells, bind to the antigens on foreign bacteria or viruses, the complement system can begin to be assembled. The complement system is comprised of nine proteins that end up forming a pore in the membrane of bacteria and viruses, allowing other defense proteins to enter and destroying the sodium-potassium gradient that is required for energy generation in bacteria. Complement is also responsible for helping recruit immune cells to the site of infection or injury.

The major histocompatibility complex proteins are responsible for presenting antigens to helper T-cells.

Example Question #78 : Immune System

An influenza vaccination administered through injection would be categorized as what type of immunization?

Possible Answers:

Active natural immunization

Passive artificial immunization

Active artificial immunization

Passive natural immunization

Correct answer:

Active artificial immunization

Explanation:

Active immunization is that which occurs as a result of the immune response of the affected individual. Passive immunization is the passing of antibodies from one entity to another, such as a pregnant mother who passes antibodies through the placenta to the fetus. Artificial immunization occurs when one is exposed to the antigen of the infection without having to experience the infection. The antigen can be a weakened or dead form of the microbe. Natural immunity is achieved when one is infected by a live form of the microbe. In both natural and artificial immunity, the immune system generates antibodies and memory cells to fight off future infections.

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