Microbiology MCQs with Answer and Explnation | Chapter 12

Answer: Proteins

They are composed of amino acids linked together by peptide bonds. The specific sequence of amino acids in an enzyme determines its shape and function. The shape of an enzyme creates a pocket, or active site, that binds to the specific molecule that the enzyme is designed to act on. This molecule is called the substrate.

The other options are incorrect:

• Lipids are a group of molecules that include fats, oils, and waxes. They are not involved in enzyme catalysis.
• Carbohydrates are a group of molecules that include sugars and starches. They are not involved in enzyme catalysis.
• Nucleic acids are a group of molecules that include DNA and RNA. They are not involved in enzyme catalysis.

Answer: Hybridoma technology

Monoclonal antibodies are produced by fusing a myeloma cell, a type of cancer cell that produces antibodies continuously, with a B lymphocyte, a type of white blood cell that produces antibodies specifically for a particular antigen. The resulting cell, called a hybridoma, is a hybrid of the two cells and has the ability to produce monoclonal antibodies indefinitely.

The other options are incorrect:

• Biotechnology is a broad term that encompasses a variety of technologies that use living organisms or their components to produce products or services.
• Fermentation technology is a process that uses microorganisms to convert sugars or starches into other products, such as alcohol or yogurt.

Answer: Unbroken skin

The skin is the largest organ in the human body, and it acts as a physical barrier that prevents pathogens from entering the body. The skin is also home to a variety of immune cells, such as macrophages and dendritic cells, which can engulf and destroy pathogens.

The other options are incorrect:

• Antibody molecules are a type of protein that is produced by the immune system in response to an infection. Antibodies bind to antigens, which are foreign substances that the body does not recognize. This binding helps to mark the antigen for destruction by other immune cells.
• Antigen molecules are molecules that are found on the surface of pathogens. They are recognized by the immune system as foreign, and they trigger the production of antibodies.
• Phagocytic cells are a type of white blood cell that can engulf and destroy pathogens. They are an important part of the immune system’s second line of defense.

Answer: Avidity

Avidity is the overall strength of the interaction between an antibody and an antigen, and it is a result of the cumulative effect of multiple antibody-antigen interactions. Avidity is influenced by the affinity of the individual antibody-antigen interactions, as well as the number of binding sites on the antigen and antibody.

The other options are incorrect:

• Affinity, on the other hand, is the strength of the interaction between a single antibody-binding site (paratope) and an antigen epitope. Affinity is a measure of the strength of the chemical bonds between the antibody and the antigen, and it is typically measured by the dissociation constant (Kd).
• Covalent bonds are the strongest type of chemical bond, and they are formed by the sharing of electrons between atoms. Covalent bonds are not involved in the interaction between antigens and antibodies.

Answer: Treponema pallidum

Syphilis is a sexually transmitted infection (STI) caused by the bacterium Treponema pallidum. It can also be passed from mother to child during pregnancy. Syphilis can cause serious health problems if left untreated, including blindness, heart disease, and brain damage.

The other options are incorrect:

• Staphylococcus aureus is a bacterium that can cause a variety of infections, including skin infections, pneumonia, and food poisoning.
• Yersinia pseudotuberculosis is a bacterium that can cause a variety of illnesses, including gastroenteritis, mesenteric lymphadenitis, and yersiniosis.
• Streptococcus syphilitis is a bacterium that does not exist.

Answer: Basophilic

The inclusions or “Negri bodies” produced by the rabies virus show characteristic basophilic (blue-staining) granules when observed under a microscope. These structures are often found in the cytoplasm of infected nerve cells and are indicative of a rabies virus infection.

The other options are incorrect:

• Eosinophilic: Eosinophilic staining is associated with structures that take up the eosin dye and appear pink under a microscope. Negri bodies in rabies virus infections are typically basophilic.
• Neutrophilic: The term “neutrophilic” is not commonly used to describe staining characteristics of structures. It is more relevant to certain types of white blood cells (neutrophils).
• Acidophilic: Acidophilic staining is associated with structures that take up acidic dyes and appear red or pink under a microscope. In the case of rabies virus Negri bodies, the characteristic staining is basophilic.

Answer: Candida utilis

It is a non-pathogenic yeast that can grow efficiently on a variety of substrates, including molasses, sulfite liquor, and whey. It has a high protein content (40-50%) and is a good source of vitamins and minerals.

The other options are correct:

• Saccharomyces cerevisiae is a yeast that is commonly used for baking and brewing. It can also be used to produce SCP, but it is not as efficient as Candida utilis.
• Rhizopus is a fungus that is commonly used to produce tempeh, a fermented soybean product. It can also be used to produce SCP, but it is not as widely used as Candida utilis.

Answer: Western blot

The analysis of protein antigens is typically done by a technique called Western blotting. Western blotting involves the separation of proteins by gel electrophoresis, followed by transfer to a membrane and detection using specific antibodies. This technique is commonly used to detect and analyze specific proteins within a complex mixture.

The other options are correct:

• Southern blot: Southern blotting is used for the detection of specific DNA sequences in a sample.
• Northern blot: Northern blotting is used for the detection of specific RNA sequences in a sample

Answer: IgG

IgG is the most abundant antibody in the blood, and it is responsible for long-term immunity. IgG is transferred from the mother to the baby through the placenta during pregnancy. This means that the baby is born with a supply of IgG that can protect it from infection until its own immune system develops.

The other options are incorrect:

• IgA is an antibody that is found in mucosal secretions, such as saliva, tears, and breast milk. It helps to protect the body from pathogens that enter the body through these routes.
• IgE is an antibody that is involved in allergic reactions.
• IgM is the first antibody produced by the immune system in response to an infection. It is a large, pentameric molecule that is very efficient at activating the complement system, which is a group of proteins that help to destroy pathogens. IgM is also very effective at agglutinating, or clumping together, pathogens, which makes it easier for them to be phagocytosed, or engulfed, by immune cells.

Answer: Retro virus group

The human immunodeficiency virus (HIV), which causes AIDS, is a retrovirus. Retroviruses are a type of virus that replicates by transcribing their RNA genome into DNA, which is then integrated into the host cell’s DNA. This allows the virus to replicate along with the host cell’s DNA.

The other options are incorrect:

• Rhabdoviruses are a type of virus that causes diseases such as rabies and vesicular stomatitis.
• Hepatitis viruses are a type of virus that causes inflammation of the liver.
• Adenoviruses are a type of virus that causes respiratory infections.

Answer: Haem agglutination

Haem agglutination is a type of complement-mediated agglutination reaction that involves the clumping of red blood cells (RBCs) in the presence of specific antibodies and complement proteins. This reaction is commonly used to detect and diagnose various infectious diseases, such as brucellosis, syphilis, and rubella.

In haem agglutination, specific antibodies bind to antigens on the surface of RBCs. These antigen-antibody complexes then activate the complement system, which leads to the formation of a C3b convertase enzyme. This enzyme cleaves C3, a complement protein, into C3a and C3b. C3b binds to the antigen-antibody complexes on the RBCs, causing them to crosslink and form clumps.

The other options are incorrect:

• Complement fixation is another type of complement-mediated reaction that involves the binding of complement proteins to antigen-antibody complexes. However, unlike haem agglutination, complement fixation does not result in visible clumping.
• Conglutination is a non-specific agglutination reaction that involves the clumping of particles, such as bacteria or RBCs, in the presence of conglutinin, a protein found in serum. Conglutinin binds to C3b molecules on the surface of the particles, causing them to crosslink and form clumps.
• Schultz-Dale phenomenon is a type of allergic reaction that involves the contraction of smooth muscle in the airways. This reaction is mediated by IgE antibodies, which bind to mast cells and trigger the release of histamine and other inflammatory mediators.

Answer: DNA

Reverse transcriptase is an enzyme involved in the synthesis of DNA. It catalyzes the synthesis of DNA from an RNA template in a process known as reverse transcription. This enzyme is particularly notable in retroviruses like HIV, where the viral RNA genome is reverse transcribed into DNA upon infection of a host cell.

The other options are incorrect:

• Soluble RNA: Soluble RNA, also known as transfer RNA (tRNA), is involved in the translation of mRNA into proteins and is not synthesized by reverse transcriptase.
• m-RNA from DNA: Transcription is the process where mRNA is synthesized from DNA, and this is not the primary function of reverse transcriptase.
• Nucleotides: While nucleotides are essential building blocks for DNA synthesis, reverse transcriptase itself is not directly involved in the synthesis of free nucleotides. It is primarily involved in synthesizing a DNA copy from an RNA template.

Answer: T cell

The cellular immune response is primarily mediated by T cells. T cells are a type of lymphocyte that plays a central role in cell-mediated immunity. They are responsible for recognizing and directly interacting with infected or abnormal cells, coordinating immune responses, and facilitating the destruction of infected cells.

The other options are incorrect:

• B cells: B cells are involved in the humoral immune response, where they produce antibodies to neutralize pathogens. They are not the primary mediators of the cellular immune response.
• BT cells: There is no specific category of immune cells referred to as “BT cells.” The primary cellular mediators are T cells.
• Endothelial cells: Endothelial cells form the lining of blood vessels and are not immune cells. They play a role in vascular function but are not directly involved in cellular immune responses.

Answer: IgG

IgG is the most abundant immunoglobulin in human serum, accounting for approximately 75-80% of total serum immunoglobulin. It is also the only immunoglobulin that can cross the placenta, providing some degree of immune protection to the developing fetus. IgG is responsible for long-term immunity against pathogens, and it is also important for opsonization, which is the process of coating pathogens with antibodies to make them more easily phagocytosed by immune cells.

The other options are incorrect:

• IgA is the most abundant immunoglobulin in mucosal secretions, such as saliva, tears, and breast milk. It is important for protecting the body from pathogens that enter through these routes.
• IgE is involved in allergic reactions.

Answer: IgE

Reagenic antibodies are a type of antibody that is responsible for mediating allergic reactions. They are also known as IgE antibodies. IgE antibodies are produced by B cells in response to exposure to allergens. When an IgE antibody binds to an allergen, it triggers the release of histamine and other inflammatory mediators from mast cells and basophils. These mediators cause the symptoms of an allergic reaction, such as sneezing, runny nose, itchy eyes, and skin rash.

The other options are incorrect:

• IgG is the most abundant immunoglobulin in the blood and is responsible for long-term immunity.
• IgA is the most abundant immunoglobulin in mucosal secretions, such as saliva, tears, and breast milk, and is important for protecting the body from pathogens that enter through these routes.
• IgM is the first antibody produced by the immune system in response to an infection and is effective at activating the complement system and agglutinating pathogens, but it does not provide long-term immunity.

Answer: Precipitation

The reaction of soluble antigen with antibody is known as precipitation. This reaction is characterized by the formation of an insoluble complex between the antigen and antibody. The size of the complex will vary depending on the ratio of antigen to antibody. If there is more antigen than antibody, the complexes will be small and will remain in suspension. If there is more antibody than antigen, the complexes will be large and will precipitate out of solution.

The other options are incorrect:

• Flocculation is a type of precipitation that occurs in the presence of electrolytes.
• Agglutination is the clumping of particles, such as cells or bacteria, in the presence of antibody.
• Complement fixation is a type of antigen-antibody reaction that involves the activation of the complement system.

Answer: Glycoprotein

Interferons are glycoproteins, meaning they are composed of both protein and carbohydrate (sugar) components. Interferons are signaling proteins that play a crucial role in the immune response to viral infections and other immune-related processes.

The other options are incorrect:

• Lipids: Lipids are molecules that include fats and related compounds. Interferons are not composed of lipids.
• Lipoprotein: Lipoproteins are complexes of lipids and proteins. Interferons are glycoproteins, not lipoproteins.
• Nucleic acid: Interferons are not composed of nucleic acids. They are proteins with a glycosylation component.

Answer: IgM

Immunoglobulin M (IgM) is a pentameric antibody, meaning it is composed of five Y-shaped subunits. This pentameric structure gives IgM a high avidity, which is the strength of the interaction between an antibody and an antigen. Avidity is important for agglutination reactions because it allows IgM antibodies to crosslink multiple antigens, which causes them to clump together.

The other options are incorrect:

• IgG is the most abundant immunoglobulin in the blood, but it has a lower avidity than IgM.
• IgA is the most abundant immunoglobulin in mucosal secretions, such as saliva and tears. It has a lower avidity than IgM and is not as effective at agglutinating antigens.
• IgD is a rare immunoglobulin that is found on the surface of B cells. It has a lower avidity than IgM and is not as effective at agglutinating antigens.

Answer: Immunotherapy

Monoclonal antibodies are laboratory-produced molecules that are engineered to mimic the immune system’s ability to recognize and attack specific cells or molecules. They are used to treat a variety of diseases, including cancer, autoimmune diseases, and infectious diseases.

The other options are incorrect:

• Gene therapy is a type of therapy that involves using genes to treat or prevent disease.
• Blood transfusion is a procedure in which blood is transferred from one person to another.
• Organ transfusion is a procedure in which an organ is transplanted from one person to another.

Answer: Monoclonal antibodies

The hybridoma technique is specifically used for the production of monoclonal antibodies. In the hybridoma technique, hybrid cells (hybridomas) are created by fusing a specific type of antibody-producing B cell with a myeloma cell (a cancerous plasma cell). The resulting hybridoma cells have the ability to produce a single type of antibody, known as a monoclonal antibody.

The other options are incorrect:

• Polyclonal antibodies: The hybridoma technique is not used for the production of polyclonal antibodies. Polyclonal antibodies are typically produced by immunizing an animal with an antigen, and they consist of a mixture of antibodies from different B cells.
• Both Monoclonal antibodies and Polyclonal antibodies: The correct answer is “Monoclonal antibodies.” While polyclonal antibodies can be generated through other methods, the hybridoma technique is specifically associated with monoclonal antibody production.

Answer: ELISA

ELISA stands for enzyme-linked immunosorbent assay. It is a type of blood test that is used to detect antibodies to HIV, the virus that causes AIDS. ELISA tests are very sensitive and specific, meaning that they are able to accurately detect HIV antibodies in the blood.

The other options are incorrect:

• Widal test is a type of blood test that is used to detect antibodies to Salmonella typhi, the bacterium that causes typhoid fever.
• Agglutination is a laboratory technique that is used to clump cells or particles together. It is not a specific test for HIV.
• CFT stands for complement fixation test. It is a type of blood test that is used to detect antibodies to various infectious diseases, including syphilis and hepatitis B. However, it is not as specific or sensitive as ELISA for detecting HIV antibodies.

Answer: IgM

Antibody valency refers to the number of antigen-binding sites an antibody has. IgM is a pentameric antibody, meaning it has five Y-shaped subunits, each with two antigen-binding sites. This gives IgM a valency of 10, making it the antibody with the highest valency.

The other options are incorrect:

• IgG is a monomeric antibody, meaning it has only one Y-shaped subunit with two antigen-binding sites. This gives IgG a valency of 2.
• IgA can be either monomeric or dimeric. Monomeric IgA has a valency of 2, while dimeric IgA has a valency of 4.
• IgD is a monomeric antibody with two antigen-binding sites. This gives IgD a valency of 2.

Answer: Affinity

The intensity of attraction between an antigen and an antibody molecule is known as “affinity.” Affinity represents the strength of the binding interaction between a single antigen-binding site on an antibody and its corresponding epitope on the antigen.

The other options are incorrect:

• Avidity: Avidity is a related but broader concept that takes into account the overall strength of binding between multiple antigen-binding sites on an antibody and multiple epitopes on an antigen. It considers both affinity and valency.
• Reaction: “Reaction” is a generic term and does not specifically describe the intensity of attraction between antigen and antibody molecules.

Answer: Infection

Active immunity is induced by exposure to an antigen, typically through infection or vaccination. When the immune system encounters a pathogen, it generates an immune response that includes the production of antibodies and memory cells. This type of immunity provides long-lasting protection against future infections with the same pathogen.

The other options are incorrect:

• Placental transfer of antibodies: This is an example of passive immunity, where antibodies are transferred from a mother to her offspring through the placenta. It does not involve the active stimulation of the immune system.
• Injection of antibodies: This is another example of passive immunity, where pre-formed antibodies are directly introduced into the body. It does not stimulate the immune system to produce its antibodies.
• Injection of gamma-globulins: Gamma-globulins are a component of antibodies. Injecting gamma-globulins provides passive immunity and is not a method of inducing active immunity.

Answer: All of the above

• Louis Pasteur, a French chemist and microbiologist, made significant contributions to the field of immunology and is credited with developing the first vaccines for anthrax, rabies, and chicken cholera.
• Anthrax vaccine: In 1881, Pasteur developed the first successful vaccine for anthrax, a deadly disease that affects livestock. He attenuated the anthrax bacterium by growing it at a higher temperature, making it less virulent but still able to stimulate an immune response.
• Rabies vaccine: In 1885, Pasteur developed a vaccine for rabies, a fatal viral disease that affects the central nervous system. He used dried spinal cords of infected rabbits to create a weakened form of the rabies virus, which could safely induce immunity.
• Chicken cholera vaccine: In 1879, Pasteur’s work on chicken cholera, a bacterial disease of chickens, led to the development of the first attenuated vaccine. He weakened the cholera bacterium by exposing it to oxygen, allowing it to induce immunity without causing the disease.

Answer: Contact dermatitis

Delayed type hypersensitivity (DTH) is a cell-mediated immune response that typically takes 48-72 hours to develop after exposure to an allergen. It is characterized by inflammation and tissue damage at the site of exposure.

The other options are incorrect:

• Penicillin allergy is an example of immediate type hypersensitivity (IH), which is an antibody-mediated response that occurs within minutes or hours of exposure to an allergen.
• Arthus reaction is a localized type III hypersensitivity reaction that is characterized by vasculitis and tissue necrosis. It is typically caused by the injection of a foreign protein, such as animal serum.
• Anaphylaxis is a severe, systemic type I hypersensitivity reaction that can be fatal. It is characterized by widespread inflammation, including bronchospasm, angioedema, and hypotension.

Answer: Ether

Freezing (-20°C to -70°C), lyophilization (freeze-drying), and formaldehyde are all commonly used methods for preserving viruses. Ether, on the other hand, is a solvent that can damage viruses and is not typically used for preservation.

Here is a brief overview of each method:

• Freezing (-20°C to -70°C): This is a simple and effective method for preserving viruses for short-term storage. Viruses can be stored in frozen aliquots at -20°C or -70°C for several months to years.
• Lyophilization (freeze-drying): This is a more complex method of preservation, but it can be used to store viruses for much longer periods of time. Lyophilization removes the water from virus samples, which prevents them from degrading. Lyophilized viruses can be stored at room temperature for many years.
• Formaldehyde: Formaldehyde is a chemical that can be used to inactivate viruses. This makes it useful for preserving viruses for diagnostic purposes. Formaldehyde-treated viruses can be stored at 4°C for several months.

Answer: All of the above

Antibody formation, also known as immunoglobin production, is a complex process that depends on several factors, including:

• Age of the person: The ability to produce antibodies declines with age, especially after the age of 65. This is why older adults are more susceptible to infections.
• Amount of antigen: The amount of antigen exposure is a key factor in determining the strength of the immune response. A stronger immune response will lead to the production of more antibodies.
• Well-being of the person: Overall health and nutrition can also affect antibody production. People who are malnourished or stressed may have a weaker immune response and produce fewer antibodies.

Answer: All of these

Local immunity plays a crucial role in protecting against various infections, including influenza, allergies, and polio.

• Influenza: Local immunity in the respiratory tract is essential for preventing influenza virus infection. IgA antibodies present in mucosal secretions, such as saliva and mucus, can neutralize the virus before it penetrates deeper into the respiratory system.
• Allergy: Local immunity in the airways helps regulate immune responses to allergens. Regulatory T cells (Tregs) and IgA antibodies in the airways suppress excessive inflammatory reactions that cause allergic symptoms, such as sneezing, runny nose, and itchy eyes.
• Polio: Local immunity in the intestines contributes to poliovirus resistance. IgA antibodies in the gut lumen can neutralize the poliovirus before it invades intestinal cells, preventing systemic infection and paralysis.

Answer: Stabilizer

Magnesium may be used as a stabilizer in vaccines. Stabilizers are substances added to vaccines to help maintain the effectiveness and stability of the vaccine over time, particularly during storage and transportation.

The other options are incorrect:

• Adjuvant: Adjuvants are substances added to vaccines to enhance the immune response to the antigen. While some adjuvants may contain elements like aluminum, magnesium is not commonly used for this purpose.
• Conditioner: “Conditioner” is not a recognized term in the context of vaccine formulation. The term used is typically “stabilizer.”

Answer: Measles

Immunity is often lifelong following natural infection with the measles virus. Individuals who have had measles typically develop long-lasting immunity against the disease.

The other options are incorrect:

• Diphtheria: Immunity following natural infection with diphtheria is not always lifelong, and booster vaccinations are recommended.
• Tetanus: Immunity following natural infection with tetanus is not always lifelong, and booster vaccinations are recommended.
• Yellow fever: Immunity following natural infection with yellow fever is typically long-lasting, and a single vaccination provides long-term protection in most cases. However, in certain situations, booster doses may be recommended

Answer: Cow-pox material

Edward Jenner used material from cowpox lesions to prepare the smallpox vaccine. He observed that milkmaids who had been infected with cowpox seemed to be immune to smallpox, leading him to hypothesize and test the concept of vaccination.

The other options are incorrect:

• Smallpox material: Jenner did not use material from smallpox lesions; instead, he used material from cowpox lesions.
• Chickenpox material: Jenner’s work was specifically related to cowpox, not chickenpox.
• Measles material: Jenner’s work was not related to measles. He focused on the relationship between cowpox and smallpox, laying the foundation for vaccination.

Answer: Hfr-Strain

During recombination in bacterial cells, the Hfr (High frequency of recombination) strain is known for frequently donating genetic material at a high rate. Hfr strains have the F factor (fertility factor) integrated into their chromosomal DNA, and during conjugation, the transfer of genetic material often includes a significant portion of the bacterial chromosome.

The other options are incorrect:

• F+-Strain: The F+ (F positive) strain has the F factor but is not integrated into the chromosomal DNA. It does not donate chromosomal DNA as extensively as the Hfr strain.
• F-Strain: The F- (F negative) strain lacks the F factor and does not donate genetic material during conjugation.
• Both Hfr-Strain and F-Strain: The Hfr-Strain is the primary strain known for high-frequency recombination. The F-Strain, which lacks the F factor, does not donate genetic material during conjugation.

Answer: Heritable

The character acquired by a cell due to recombination is considered heritable. This means that the genetic changes resulting from recombination can be passed on to subsequent generations of cells through cell division.

The other options are incorrect:

• Inheritable: This is a synonym for “heritable” and is correct in the context of genetic changes passed on to offspring cells.
• Suppressed: Recombination does not necessarily suppress genetic information. It can lead to the expression of new traits.
• Dominating: The character acquired through recombination may or may not be dominating. It depends on the specific genetic interactions involved.

Answer: Thymus

T-cells (or T lymphocytes) undergo maturation in the thymus, a primary lymphoid organ. T-cells originate from hematopoietic stem cells in the bone marrow but complete their development and maturation in the thymus.

The other options are incorrect:

• Bone marrow: While T-cells originate from hematopoietic stem cells in the bone marrow, their maturation occurs in the thymus.
• Spleen: The spleen is a secondary lymphoid organ involved in immune responses, but it is not the site where T-cells are produced. T-cells mature in the thymus.

Answer: B-cells

Antibodies are produced by B cells, a type of white blood cell that is part of the adaptive immune system. B cells are activated by T cells when they encounter an antigen, which is a foreign substance that the body does not recognize. Once activated, B cells divide and differentiate into plasma cells, which are antibody-secreting cells. Plasma cells produce and release antibodies into the bloodstream, where they can bind to the antigen and neutralize it.

The other options are incorrect:

• T cells are not responsible for producing antibodies. Their main function is to recognize and kill infected cells.
• â-cells are a type of pancreatic islet cell that produces insulin, the hormone that regulates blood sugar levels.
• NK cells are a type of lymphocyte that is part of the innate immune system. They can kill infected cells and tumor cells without prior activation.
• Eosinophils are a type of white blood cell that is involved in allergic reactions and parasitic infections.

Answer: Haptens

Incomplete antigens, also known as haptens, are small molecules that are not immunogenic by themselves. This means that they cannot stimulate the immune system to produce antibodies without the help of a carrier protein. Carrier proteins are usually large, immunogenic molecules that act as a scaffold for haptens. When a hapten is attached to a carrier protein, it becomes an immunogen and can stimulate the immune system to produce antibodies.

The other options are incorrect:

• Immunogens are molecules that can stimulate the immune system to produce antibodies. Haptens are a type of immunogen, but they are incomplete immunogens.
• Epitopes are the part of an antigen that is recognized by antibodies. Haptens are not epitopes, but they can contain epitopes.
• Paratopes are the part of an antibody that binds to an epitope. Haptens are not paratopes, but they can be bound by paratopes.

Answer: Both High molecular weight and Chemical complexity

• High molecular weight (>8,000 Daltons): A minimum molecular weight is essential for the antigen to elicit an immune response. This is because the immune system’s receptors, such as antibodies, need to recognize specific molecular structures on the antigen surface. Larger molecules, with more complex structures, offer more surface area for recognition.
• Chemical complexity: The antigen’s chemical structure should be sufficiently complex to provide distinct molecular features that can be recognized by the immune system’s receptors. This complexity arises from the arrangement and interactions of the molecule’s amino acid chains, which create unique conformations and chemical properties.

Both of these features are crucial for an antigen to effectively stimulate an immune response. If an antigen lacks either high molecular weight or chemical complexity, it may not be able to induce the appropriate immune mechanisms to neutralize or eliminate the foreign substance.

Answer: Lymph nodes

Lymph nodes are small, bean-shaped structures that filter lymph as it flows through the lymphatic system. Lymph nodes contain immune cells and serve as sites where foreign substances, such as pathogens or antigens, are filtered and immune responses are initiated.

The other options are incorrect:

• Spleen: The spleen also plays a role in filtering blood, removing damaged blood cells and pathogens. However, it is not primarily involved in filtering lymph.
• Thymus: The thymus is involved in the maturation of T-cells (a type of immune cell) but is not a primary site for filtering lymph.
• Bone marrow: The bone marrow is involved in the production of blood cells, including lymphocytes, but it is not a site for filtering lymph.

Answer: Lymphocytes

Lymphocytes are the primary cells involved in the immune response. There are two main types of lymphocytes: B-cells and T-cells. B-cells are responsible for antibody production, while T-cells play a central role in cell-mediated immunity. Both types of lymphocytes coordinate immune responses to defend the body against pathogens.

The other options are incorrect:

• NK-cells: Natural Killer (NK) cells are a type of lymphocyte involved in the innate immune response. They play a role in the early defense against certain infections and cancer cells.
• K-cells: “K-cells” is not a recognized term in the context of immune cells. The primary cells are lymphocytes.

Answer: B-cells

Plasma cells are the end cells or effector cells of B-cells (B lymphocytes). B-cells, when activated by an antigen, can differentiate into plasma cells. Plasma cells are specialized for antibody production, and they secrete large amounts of antibodies into the bloodstream.

The other options are incorrect:

• T-cells: T-cells (T lymphocytes) are a different subset of immune cells involved in cell-mediated immunity. They do not differentiate into plasma cells.
• β-cells: “β-cells” is a term often associated with pancreatic beta cells, which are involved in insulin production. In the context of the immune system, plasma cells arise from B-cells.
• Killer cells: “Killer cells” is a general term that may refer to cytotoxic cells, such as cytotoxic T-cells. However, plasma cells are not derived from killer cells.

Answer: IgE

Basophils are a type of granulocyte, a type of white blood cell that is involved in the immune response. IgE is a type of antibody that is involved in allergic reactions. When IgE binds to the FcεRI receptor on the surface of a basophil, it triggers the basophil to release histamine and other inflammatory mediators. These mediators cause the symptoms of an allergic reaction, such as swelling, itching, and difficulty breathing.

The other options are incorrect:

• IgG is the most abundant antibody in the blood. It is important for protecting the body from bacterial infections. Basophils do not have receptors for IgG.
• IgA is the most abundant antibody in the secretions of the body, such as saliva, tears, and breast milk. It is important for protecting the body from infections at the mucosal surfaces. Basophils do not have receptors for IgA.
• IgM is the first antibody that is produced in response to an infection. It is important for activating the complement system, which is a group of proteins that help to destroy pathogens. Basophils do not have receptors for IgM.

Answer: Hidden epitopes

Denaturation can lead to the alteration or masking of epitopes on antigens, making them functionless or hidden. Hidden epitopes refer to epitopes that become inaccessible or less recognizable due to changes in the three-dimensional structure of the antigen.

The other options are incorrect:

• Cross-reactive antigens: Cross-reactive antigens are antigens that can elicit immune responses similar to those elicited by a different but related antigen.
• Epitopes: Epitopes are specific regions on antigens recognized by the immune system. Denaturation can affect the accessibility of epitopes.
• Forssman antigens: Forssman antigens are specific blood group antigens and are not directly related to the concept of hidden epitopes due to denaturation.

Answer: Denaturation

The capacity of an antigen to break down into small fragments, each with a single epitopic region, is associated with denaturation. Denaturation refers to the alteration of the three-dimensional structure of a protein, which can result in the exposure of hidden or masked epitopes and the breakdown of the antigen into smaller fragments.

The other options are incorrect:

• Solubility: Solubility refers to the ability of a substance to dissolve in a solvent. It is not directly related to the breakdown of an antigen into epitopic fragments.
• Foreignness: Foreignness refers to the degree of dissimilarity between an antigen and the host’s own molecules. It is not directly related to the breakdown of an antigen into epitopic fragments.

Answer: Steric configuration

Antigenic specificity, the ability of an antigen to be recognized by a specific antibody or T-cell receptor, is primarily due to steric configuration. The three-dimensional arrangement of atoms in an antigen determines its specificity, allowing it to interact with the complementary binding site on an antibody or T-cell receptor.

The other options are incorrect:

• Chemical complexity: While chemical complexity contributes to antigenic properties, it is not the primary factor determining specificity. Antigenic specificity is more closely related to the specific arrangement of atoms.
• Solubility: Solubility is not a major determinant of antigenic specificity. The key factor is the molecular structure and shape.

Answer: Glycoproteins

Antibodies, also known as immunoglobulins, are glycoproteins. They are proteins with attached carbohydrate molecules. The structure of antibodies includes two heavy chains and two light chains, and the carbohydrate portions contribute to their stability and function.

The other options are incorrect:

• Proteins are a type of macromolecule that consists of chains of amino acids. Antibodies are a type of protein, but they are also glycoproteins, meaning they have carbohydrate molecules attached to them.
• Phospholipids are a type of lipid that is found in the cell membrane. They are not involved in the immune response.

Answer: IgG

IgG (Immunoglobulin G) is considered a general-purpose antibody and is the most abundant immunoglobulin in the bloodstream. It plays a major role in secondary immune responses, crosses the placenta during pregnancy to provide passive immunity to the fetus, and contributes to the opsonization of pathogens.

The other options are incorrect:

• IgA is the most abundant antibody in the secretions of the body, such as saliva, tears, and breast milk. It is important for protecting the body from infections at the mucosal surfaces.
• IgM is the first antibody that is produced in response to an infection. It is important for activating the complement system, which is a group of proteins that help to destroy pathogens.
• IgD is found in very low levels in the blood and is thought to play a role in B-cell maturation.

Answer: IgA

The antibody present in colostrums is IgA. IgA is the most abundant antibody in colostrums, which is the thick, yellow-colored breast milk that is produced by women shortly after childbirth. IgA is important for protecting the newborn from infections, as it can prevent pathogens from attaching to the cells lining the intestines.

The other options are incorrect:

• IgG is the most abundant antibody in the blood. It is important for protecting the body from bacterial infections. IgG is not present in colostrums in significant amounts.
• IgM is the first antibody that is produced in response to an infection. It is important for activating the complement system, which is a group of proteins that help to destroy pathogens. IgM is not present in colostrums in significant amounts.
• IgE is involved in allergic reactions. It is not present in colostrums in significant amounts.

Answer: IgM

IgM (Immunoglobulin M) is often referred to as the “millionaire molecule” because it is the largest antibody in terms of molecular size. IgM is a pentameric molecule, meaning it consists of five antibody units linked together. This large size contributes to its effectiveness in agglutination and complement activation.

The other options are incorrect:

• IgA is the most abundant antibody in the secretions of the body, such as saliva, tears, and breast milk. It is important for protecting the body from infections at the mucosal surfaces.
• IgG is the most abundant antibody in the blood. It is important for protecting the body from bacterial infections.
• IgD is found in very low levels in the blood and is thought to play a role in B-cell maturation.

Answer: Ishizaka

IgE (Immunoglobulin E) was discovered by Kimishige Ishizaka and Teruko Ishizaka in the 1960s. They identified IgE as a distinct immunoglobulin class and demonstrated its association with allergic reactions and hypersensitivity.

The other options are incorrect:

• Porter discovered the four main classes of antibodies: IgG, IgA, IgM, and IgD.
• Richet discovered the concept of hypersensitivity reactions, which are the basis of allergies.