MCB 3020C Exam 4 V1 | MCB 3020C General Microbiology | Actual
Q&A with Rationale (MCB3020C Exam 4) | University of Central
Florida
1. Which component of the innate immune system is specifically responsible for cleaving the
glycosidic bonds in bacterial peptidoglycan?
A. Defensin
B. Transferrin
C. Lysozyme
D. Complement C3b
Answer: C
Explanation: Lysozyme is an enzyme found in secretions like tears and saliva that targets
the cell walls of bacteria. It specifically breaks the chemical bonds between the NAG and
NAM subunits of peptidoglycan, leading to osmotic lysis. This action provides a significant
primary defense against Gram-positive organisms.
2. In the process of phagocytosis, which stage involves the fusion of the phagosome with a
lysosome?
A. Chemotaxis
B. Adherence
C. Digestion
D. Ingestion
Answer: C
Explanation: The digestion phase occurs after a microbe has been internalized into a
phagosome. During this stage, the phagosome fuses with a lysosome to form a
phagolysosome, which contains digestive enzymes and reactive oxygen species. These
components work together to kill and break down the ingested pathogen.
3. What is the primary function of the C3b protein in the complement system?
A. Opsonization to enhance phagocytosis
B. Triggering the inflammatory response
C. Formation of the membrane attack complex
D. Inducing apoptosis in viral infected cells
Answer: A
,Explanation: C3b is a critical component of the complement cascade that functions as an
opsonin. By coating the surface of a pathogen, it makes it more recognizable and easier for
phagocytes to bind and engulf. This process effectively bridges the gap between innate
recognition and cellular destruction.
4. During inflammation, what is the primary purpose of vasodilation?
A. To decrease the temperature at the site of infection
B. To prevent the spread of toxins to the liver
C. To stimulate the production of antibodies by B cells
D. To increase blood flow and delivery of white blood cells to the injured area
Answer: D
Explanation: Vasodilation increases the diameter of blood vessels, which allows for a
greater volume of blood to reach the site of injury or infection. This increased flow brings
essential immune cells, such as neutrophils and monocytes, and various clotting factors to
the area. Furthermore, it results in the characteristic redness and heat associated with the
inflammatory response.
5. Which type of interferon is primarily produced by virus-infected cells to warn neighboring
cells?
A. Interferon-delta
B. Interferon-gamma
C. Interferon-alpha and Interferon-beta
D. Interferon-omega
Answer: C
Explanation: Type I interferons, specifically alpha and beta, are secreted by cells that have
been infected by a virus. They bind to receptors on nearby uninfected cells, stimulating the
production of antiviral proteins (AVPs) that inhibit viral replication. This mechanism helps
to limit the spread of the viral infection within the host tissue.
6. Which class of antibody is the most abundant in serum and is the only one capable of
crossing the placenta?
A. IgG
B. IgA
C. IgM
D. IgE
Answer: A
, Explanation: IgG is the primary antibody involved in the secondary immune response and
makes up approximately 80% of all serum antibodies. It is uniquely equipped with a
structure that allows it to cross the placental barrier, providing passive immunity to the
fetus. This protection is vital for the newborn during the first few months of life.
7. Which molecule is found on the surface of all nucleated cells and is used to present
endogenous antigens to CD8+ T cells?
A. B-cell Receptor
B. MHC Class II
C. CD4 Receptor
D. MHC Class I
Answer: D
Explanation: MHC Class I molecules are expressed by all nucleated cells in the human body
and serve as a reporting system for intracellular health. They present fragments of proteins
synthesized within the cell to Cytotoxic T Lymphocytes (CTLs). If the presented peptide is
foreign, such as a viral protein, the CTL will initiate the destruction of the infected cell.
8. Helper T cells are characterized by the presence of which surface marker?
A. CD8
B. CD19
C. CD4
D. CD56
Answer: C
Explanation: CD4 is a glycoprotein found on the surface of helper T cells that acts as a co-
receptor for the T-cell receptor (TCR). It specifically interacts with MHC Class II molecules
on antigen-presenting cells to ensure proper binding. This interaction is essential for the
activation of the helper T cell and the subsequent release of cytokines.
9. What is the term for a small, non-immunogenic molecule that only becomes antigenic
when attached to a larger carrier protein?
A. Hapten
B. Epitope
C. Adjuvant
D. Antigenic determinant
Answer: A
Q&A with Rationale (MCB3020C Exam 4) | University of Central
Florida
1. Which component of the innate immune system is specifically responsible for cleaving the
glycosidic bonds in bacterial peptidoglycan?
A. Defensin
B. Transferrin
C. Lysozyme
D. Complement C3b
Answer: C
Explanation: Lysozyme is an enzyme found in secretions like tears and saliva that targets
the cell walls of bacteria. It specifically breaks the chemical bonds between the NAG and
NAM subunits of peptidoglycan, leading to osmotic lysis. This action provides a significant
primary defense against Gram-positive organisms.
2. In the process of phagocytosis, which stage involves the fusion of the phagosome with a
lysosome?
A. Chemotaxis
B. Adherence
C. Digestion
D. Ingestion
Answer: C
Explanation: The digestion phase occurs after a microbe has been internalized into a
phagosome. During this stage, the phagosome fuses with a lysosome to form a
phagolysosome, which contains digestive enzymes and reactive oxygen species. These
components work together to kill and break down the ingested pathogen.
3. What is the primary function of the C3b protein in the complement system?
A. Opsonization to enhance phagocytosis
B. Triggering the inflammatory response
C. Formation of the membrane attack complex
D. Inducing apoptosis in viral infected cells
Answer: A
,Explanation: C3b is a critical component of the complement cascade that functions as an
opsonin. By coating the surface of a pathogen, it makes it more recognizable and easier for
phagocytes to bind and engulf. This process effectively bridges the gap between innate
recognition and cellular destruction.
4. During inflammation, what is the primary purpose of vasodilation?
A. To decrease the temperature at the site of infection
B. To prevent the spread of toxins to the liver
C. To stimulate the production of antibodies by B cells
D. To increase blood flow and delivery of white blood cells to the injured area
Answer: D
Explanation: Vasodilation increases the diameter of blood vessels, which allows for a
greater volume of blood to reach the site of injury or infection. This increased flow brings
essential immune cells, such as neutrophils and monocytes, and various clotting factors to
the area. Furthermore, it results in the characteristic redness and heat associated with the
inflammatory response.
5. Which type of interferon is primarily produced by virus-infected cells to warn neighboring
cells?
A. Interferon-delta
B. Interferon-gamma
C. Interferon-alpha and Interferon-beta
D. Interferon-omega
Answer: C
Explanation: Type I interferons, specifically alpha and beta, are secreted by cells that have
been infected by a virus. They bind to receptors on nearby uninfected cells, stimulating the
production of antiviral proteins (AVPs) that inhibit viral replication. This mechanism helps
to limit the spread of the viral infection within the host tissue.
6. Which class of antibody is the most abundant in serum and is the only one capable of
crossing the placenta?
A. IgG
B. IgA
C. IgM
D. IgE
Answer: A
, Explanation: IgG is the primary antibody involved in the secondary immune response and
makes up approximately 80% of all serum antibodies. It is uniquely equipped with a
structure that allows it to cross the placental barrier, providing passive immunity to the
fetus. This protection is vital for the newborn during the first few months of life.
7. Which molecule is found on the surface of all nucleated cells and is used to present
endogenous antigens to CD8+ T cells?
A. B-cell Receptor
B. MHC Class II
C. CD4 Receptor
D. MHC Class I
Answer: D
Explanation: MHC Class I molecules are expressed by all nucleated cells in the human body
and serve as a reporting system for intracellular health. They present fragments of proteins
synthesized within the cell to Cytotoxic T Lymphocytes (CTLs). If the presented peptide is
foreign, such as a viral protein, the CTL will initiate the destruction of the infected cell.
8. Helper T cells are characterized by the presence of which surface marker?
A. CD8
B. CD19
C. CD4
D. CD56
Answer: C
Explanation: CD4 is a glycoprotein found on the surface of helper T cells that acts as a co-
receptor for the T-cell receptor (TCR). It specifically interacts with MHC Class II molecules
on antigen-presenting cells to ensure proper binding. This interaction is essential for the
activation of the helper T cell and the subsequent release of cytokines.
9. What is the term for a small, non-immunogenic molecule that only becomes antigenic
when attached to a larger carrier protein?
A. Hapten
B. Epitope
C. Adjuvant
D. Antigenic determinant
Answer: A
