UAMS Microbiology Exam 2
questions with complete solutions
Module
UAMS Microbiology
1. Which bacterial structure is primarily responsible for maintaining cell shape and
preventing osmotic lysis?
A. Capsule
B. Peptidoglycan cell wall
C. Ribosome
D. Plasma membrane
Answer: B. Peptidoglycan cell wall
Rationale: Peptidoglycan provides structural rigidity to the bacterial cell wall and helps protect
bacteria from osmotic lysis. Gram-positive bacteria have a thick peptidoglycan layer, whereas
Gram-negative bacteria have a thinner layer located in the periplasmic space.
2. Which component is characteristic of the outer membrane of Gram-negative bacteria?
A. Teichoic acid
B. Lipopolysaccharide
C. Chitin
D. Mycolic acid
Answer: B. Lipopolysaccharide
Rationale: Gram-negative bacteria possess an outer membrane containing lipopolysaccharide
(LPS). The lipid A component of LPS functions as endotoxin and can contribute to fever,
inflammation, hypotension, and septic shock.
3. Which portion of lipopolysaccharide is responsible for its endotoxin activity?
A. O antigen
B. Core polysaccharide
C. Lipid A
D. Capsule
Answer: C. Lipid A
Rationale: Lipid A is the endotoxin component of LPS. Release of substantial amounts can
trigger inflammatory cytokine production and systemic effects.
4. A bacterium appears purple after Gram staining. Which characteristic best explains this
result?
,A. It has an outer membrane rich in LPS
B. It has a thick peptidoglycan layer that retains the crystal violet-iodine complex
C. It lacks a cell wall
D. It contains mycolic acid
Answer: B. It has a thick peptidoglycan layer that retains the crystal violet-iodine complex
Rationale: Gram-positive bacteria have a thick peptidoglycan layer that retains the crystal violet-
iodine complex during the decolorization step.
5. Which structure allows many bacteria to move through liquid environments?
A. Capsule
B. Flagellum
C. Ribosome
D. Inclusion body
Answer: B. Flagellum
Rationale: Flagella are specialized structures involved in bacterial motility. Their rotation can
propel bacteria through liquid or across surfaces.
6. What is the primary function of bacterial fimbriae?
A. ATP production
B. Attachment to host cells or surfaces
C. DNA replication
D. Protein synthesis
Answer: B. Attachment to host cells or surfaces
Rationale: Fimbriae are short, hairlike structures that facilitate adhesion to host tissues and other
surfaces. Adhesion can be an important early step in colonization.
7. Which bacterial structure is most directly associated with conjugative DNA transfer?
A. Sex pilus
B. Capsule
C. Endospore
D. Flagellum
Answer: A. Sex pilus
Rationale: During bacterial conjugation, a conjugative pilus helps establish contact between
donor and recipient cells, allowing transfer of genetic material such as plasmid DNA.
8. Which process involves direct transfer of DNA from one bacterium to another through
cell-to-cell contact?
,A. Transformation
B. Transduction
C. Conjugation
D. Translation
Answer: C. Conjugation
Rationale: Conjugation requires direct cell-to-cell contact and commonly involves transfer of
plasmids through a conjugative apparatus.
9. A bacterium acquires naked DNA fragments from its environment. Which process has
occurred?
A. Transformation
B. Conjugation
C. Transduction
D. Binary fission
Answer: A. Transformation
Rationale: Transformation occurs when bacteria take up free or naked DNA from their
surroundings and incorporate it into their genetic material.
10. A bacteriophage transfers bacterial DNA from one bacterial cell to another. Which
process is this?
A. Transformation
B. Transduction
C. Conjugation
D. Translation
Answer: B. Transduction
Rationale: Transduction is bacteriophage-mediated transfer of bacterial genetic material between
cells.
11. Which mechanism can spread antibiotic-resistance genes among bacteria?
A. Horizontal gene transfer
B. Binary fission only
C. Endospore formation only
D. Glycolysis
Answer: A. Horizontal gene transfer
Rationale: Transformation, transduction, and conjugation are forms of horizontal gene transfer
and can contribute to the spread of antimicrobial-resistance genes.
, 12. Which enzyme is responsible for synthesizing a new DNA strand during bacterial DNA
replication?
A. DNA polymerase
B. RNA polymerase
C. Peptidase
D. Reverse transcriptase
Answer: A. DNA polymerase
Rationale: DNA polymerases add nucleotides to a growing DNA strand using a template strand.
13. DNA replication is described as semiconservative because:
A. Both daughter molecules contain only newly synthesized DNA
B. Each daughter DNA molecule contains one parental strand and one newly synthesized strand
C. DNA is replicated only during cell division
D. RNA replaces one DNA strand
Answer: B. Each daughter DNA molecule contains one parental strand and one newly
synthesized strand
Rationale: During semiconservative replication, each daughter DNA molecule consists of one
original parental strand and one newly synthesized complementary strand.
14. Which enzyme separates the two DNA strands at the replication fork?
A. Ligase
B. Helicase
C. Primase
D. RNA polymerase
Answer: B. Helicase
Rationale: Helicase unwinds the DNA double helix by disrupting hydrogen bonds between
complementary bases.
15. What is the primary function of DNA ligase during DNA replication?
A. Unwind DNA
B. Add RNA primers
C. Join DNA fragments
D. Destroy ribosomes
Answer: C. Join DNA fragments
Rationale: DNA ligase seals breaks between adjacent DNA fragments, including Okazaki
fragments synthesized on the lagging strand.
questions with complete solutions
Module
UAMS Microbiology
1. Which bacterial structure is primarily responsible for maintaining cell shape and
preventing osmotic lysis?
A. Capsule
B. Peptidoglycan cell wall
C. Ribosome
D. Plasma membrane
Answer: B. Peptidoglycan cell wall
Rationale: Peptidoglycan provides structural rigidity to the bacterial cell wall and helps protect
bacteria from osmotic lysis. Gram-positive bacteria have a thick peptidoglycan layer, whereas
Gram-negative bacteria have a thinner layer located in the periplasmic space.
2. Which component is characteristic of the outer membrane of Gram-negative bacteria?
A. Teichoic acid
B. Lipopolysaccharide
C. Chitin
D. Mycolic acid
Answer: B. Lipopolysaccharide
Rationale: Gram-negative bacteria possess an outer membrane containing lipopolysaccharide
(LPS). The lipid A component of LPS functions as endotoxin and can contribute to fever,
inflammation, hypotension, and septic shock.
3. Which portion of lipopolysaccharide is responsible for its endotoxin activity?
A. O antigen
B. Core polysaccharide
C. Lipid A
D. Capsule
Answer: C. Lipid A
Rationale: Lipid A is the endotoxin component of LPS. Release of substantial amounts can
trigger inflammatory cytokine production and systemic effects.
4. A bacterium appears purple after Gram staining. Which characteristic best explains this
result?
,A. It has an outer membrane rich in LPS
B. It has a thick peptidoglycan layer that retains the crystal violet-iodine complex
C. It lacks a cell wall
D. It contains mycolic acid
Answer: B. It has a thick peptidoglycan layer that retains the crystal violet-iodine complex
Rationale: Gram-positive bacteria have a thick peptidoglycan layer that retains the crystal violet-
iodine complex during the decolorization step.
5. Which structure allows many bacteria to move through liquid environments?
A. Capsule
B. Flagellum
C. Ribosome
D. Inclusion body
Answer: B. Flagellum
Rationale: Flagella are specialized structures involved in bacterial motility. Their rotation can
propel bacteria through liquid or across surfaces.
6. What is the primary function of bacterial fimbriae?
A. ATP production
B. Attachment to host cells or surfaces
C. DNA replication
D. Protein synthesis
Answer: B. Attachment to host cells or surfaces
Rationale: Fimbriae are short, hairlike structures that facilitate adhesion to host tissues and other
surfaces. Adhesion can be an important early step in colonization.
7. Which bacterial structure is most directly associated with conjugative DNA transfer?
A. Sex pilus
B. Capsule
C. Endospore
D. Flagellum
Answer: A. Sex pilus
Rationale: During bacterial conjugation, a conjugative pilus helps establish contact between
donor and recipient cells, allowing transfer of genetic material such as plasmid DNA.
8. Which process involves direct transfer of DNA from one bacterium to another through
cell-to-cell contact?
,A. Transformation
B. Transduction
C. Conjugation
D. Translation
Answer: C. Conjugation
Rationale: Conjugation requires direct cell-to-cell contact and commonly involves transfer of
plasmids through a conjugative apparatus.
9. A bacterium acquires naked DNA fragments from its environment. Which process has
occurred?
A. Transformation
B. Conjugation
C. Transduction
D. Binary fission
Answer: A. Transformation
Rationale: Transformation occurs when bacteria take up free or naked DNA from their
surroundings and incorporate it into their genetic material.
10. A bacteriophage transfers bacterial DNA from one bacterial cell to another. Which
process is this?
A. Transformation
B. Transduction
C. Conjugation
D. Translation
Answer: B. Transduction
Rationale: Transduction is bacteriophage-mediated transfer of bacterial genetic material between
cells.
11. Which mechanism can spread antibiotic-resistance genes among bacteria?
A. Horizontal gene transfer
B. Binary fission only
C. Endospore formation only
D. Glycolysis
Answer: A. Horizontal gene transfer
Rationale: Transformation, transduction, and conjugation are forms of horizontal gene transfer
and can contribute to the spread of antimicrobial-resistance genes.
, 12. Which enzyme is responsible for synthesizing a new DNA strand during bacterial DNA
replication?
A. DNA polymerase
B. RNA polymerase
C. Peptidase
D. Reverse transcriptase
Answer: A. DNA polymerase
Rationale: DNA polymerases add nucleotides to a growing DNA strand using a template strand.
13. DNA replication is described as semiconservative because:
A. Both daughter molecules contain only newly synthesized DNA
B. Each daughter DNA molecule contains one parental strand and one newly synthesized strand
C. DNA is replicated only during cell division
D. RNA replaces one DNA strand
Answer: B. Each daughter DNA molecule contains one parental strand and one newly
synthesized strand
Rationale: During semiconservative replication, each daughter DNA molecule consists of one
original parental strand and one newly synthesized complementary strand.
14. Which enzyme separates the two DNA strands at the replication fork?
A. Ligase
B. Helicase
C. Primase
D. RNA polymerase
Answer: B. Helicase
Rationale: Helicase unwinds the DNA double helix by disrupting hydrogen bonds between
complementary bases.
15. What is the primary function of DNA ligase during DNA replication?
A. Unwind DNA
B. Add RNA primers
C. Join DNA fragments
D. Destroy ribosomes
Answer: C. Join DNA fragments
Rationale: DNA ligase seals breaks between adjacent DNA fragments, including Okazaki
fragments synthesized on the lagging strand.
