MOLECULAR BIOLOGY OF THE CELL, SIXTH EDITION
CHAPTER 23: PATHOGENS AND INFECTION
1. Indicate true (T) and false (F) statements below regarding the human microbiota. Your
answer would be a four-letter string composed of letters T and F only, e.g. TFTT.
( ) The number of human cells in our body is greater than the number of bacterial,
fungal, and protozoan cells of our normal flora.
( ) There are far more genes in our microbiome than in our own genome.
( ) Infectious diseases currently cause more human deaths than cardiovascular diseases
and cancers combined.
( ) All of the microorganisms that constitute the normal flora are nonpathogens.
2. Indicate whether each of the following examples better applies to commensalism (C),
mutualism (M), or parasitism (P) in the interaction between a host and a microbe. Your answer
would be a four-letter string composed of letters C, M, and P only, e.g. CCPP.
( ) Due to poor public sanitation, a child catches cholera.
( ) A mouse is infected with a virus but shows no noticeable health defect whatsoever.
( ) Biotin and other vitamins produced by intestinal microbiota are regularly absorbed in
the human intestine.
( ) Bacteria on the skin of cattle produce antifungal compounds.
3. Which of the following illnesses is NOT associated with infection with the pathogen
indicated?
A. Cervical cancer associated with human papillomavirus infection
B. Cancer in chickens associated with Rous sarcoma virus infection
C. Colon cancer associated with Vibrio cholerae infection
D. Stomach cancer associated with Helicobacter pylori infection
E. Atherosclerosis associated with Chlamydia pneumoniae
4. Mycobacterium tuberculosis can cause tuberculosis, a life-threatening lung infection, but
can also infect an individual asymptomatically for years. It is not considered to be part of the
normal flora, and can infect healthy individuals upon exposure. It can only replicate in the host
and thus mainly spreads by direct human contact. Mycobacterium tuberculosis is therefore …
A. a facultative primary pathogen.
B. a facultative opportunistic pathogen.
, C. an obligate primary pathogen.
D. an obligate opportunistic pathogen.
5. In Gram staining, crystal violet (a violet dye) is used to specifically stain Gram-positive
bacteria. After performing Gram staining on a bacterial sample taken from an infected animal
tissue, you observe the results with a microscope. You find two major types of bacteria in the
sample, as shown in the schematic drawing below. According to these results, indicate whether
each of the following statements is correct (C) or incorrect (I). Your answer would be a three-
letter string composed of letters C and I only, e.g. CCC.
2 µm
( ) The Gram-positive bacteria in this sample are bacilli.
( ) Crystal violet stains lipopolysaccharide (LPS).
( ) The bacteria stained violet in this sample have a thicker layer of peptidoglycan
compared to the other bacteria.
6. In the following simplified diagram, three mechanisms for the horizontal transfer of
virulence genes to an avirulent bacterium are depicted. Indicate which mechanism (A to C)
corresponds to conjugation, transduction, and transformation, respectively. Your answer would
be a three-letter string composed of letters A to C only, e.g. CAB.
, A
B
C
7. How has pathogenicity in pandemic strains of Vibrio cholerae been acquired?
A. By transformation
B. By transduction
C. By conjugation
D. By vertical gene transfer
8. You infect human epithelial cells in culture with either nonpathogenic bacteria or Vibrio
cholerae, each without any further treatment, in the presence of MDC (an inhibitor of clathrin-
dependent endocytosis) or in the presence of filipin (an inhibitor of a clathrin-independent
endocytic pathway). You then measure the intracellular concentration of cyclic AMP (in
picomoles per milligram of total cell protein) and summarize the results in the following table.
Which row (1 or 2) do you think corresponds to infection with V. cholerae? From these results,
does cholera toxin enter the cell in clathrin-coated vesicles?
Treatment
No drug MDC Filipin
1 1 1 1
Infection
2 400 390 15
A. Row 1; yes
B. Row 1; no
C. Row 2; yes
D. Row 2; no
CHAPTER 23: PATHOGENS AND INFECTION
1. Indicate true (T) and false (F) statements below regarding the human microbiota. Your
answer would be a four-letter string composed of letters T and F only, e.g. TFTT.
( ) The number of human cells in our body is greater than the number of bacterial,
fungal, and protozoan cells of our normal flora.
( ) There are far more genes in our microbiome than in our own genome.
( ) Infectious diseases currently cause more human deaths than cardiovascular diseases
and cancers combined.
( ) All of the microorganisms that constitute the normal flora are nonpathogens.
2. Indicate whether each of the following examples better applies to commensalism (C),
mutualism (M), or parasitism (P) in the interaction between a host and a microbe. Your answer
would be a four-letter string composed of letters C, M, and P only, e.g. CCPP.
( ) Due to poor public sanitation, a child catches cholera.
( ) A mouse is infected with a virus but shows no noticeable health defect whatsoever.
( ) Biotin and other vitamins produced by intestinal microbiota are regularly absorbed in
the human intestine.
( ) Bacteria on the skin of cattle produce antifungal compounds.
3. Which of the following illnesses is NOT associated with infection with the pathogen
indicated?
A. Cervical cancer associated with human papillomavirus infection
B. Cancer in chickens associated with Rous sarcoma virus infection
C. Colon cancer associated with Vibrio cholerae infection
D. Stomach cancer associated with Helicobacter pylori infection
E. Atherosclerosis associated with Chlamydia pneumoniae
4. Mycobacterium tuberculosis can cause tuberculosis, a life-threatening lung infection, but
can also infect an individual asymptomatically for years. It is not considered to be part of the
normal flora, and can infect healthy individuals upon exposure. It can only replicate in the host
and thus mainly spreads by direct human contact. Mycobacterium tuberculosis is therefore …
A. a facultative primary pathogen.
B. a facultative opportunistic pathogen.
, C. an obligate primary pathogen.
D. an obligate opportunistic pathogen.
5. In Gram staining, crystal violet (a violet dye) is used to specifically stain Gram-positive
bacteria. After performing Gram staining on a bacterial sample taken from an infected animal
tissue, you observe the results with a microscope. You find two major types of bacteria in the
sample, as shown in the schematic drawing below. According to these results, indicate whether
each of the following statements is correct (C) or incorrect (I). Your answer would be a three-
letter string composed of letters C and I only, e.g. CCC.
2 µm
( ) The Gram-positive bacteria in this sample are bacilli.
( ) Crystal violet stains lipopolysaccharide (LPS).
( ) The bacteria stained violet in this sample have a thicker layer of peptidoglycan
compared to the other bacteria.
6. In the following simplified diagram, three mechanisms for the horizontal transfer of
virulence genes to an avirulent bacterium are depicted. Indicate which mechanism (A to C)
corresponds to conjugation, transduction, and transformation, respectively. Your answer would
be a three-letter string composed of letters A to C only, e.g. CAB.
, A
B
C
7. How has pathogenicity in pandemic strains of Vibrio cholerae been acquired?
A. By transformation
B. By transduction
C. By conjugation
D. By vertical gene transfer
8. You infect human epithelial cells in culture with either nonpathogenic bacteria or Vibrio
cholerae, each without any further treatment, in the presence of MDC (an inhibitor of clathrin-
dependent endocytosis) or in the presence of filipin (an inhibitor of a clathrin-independent
endocytic pathway). You then measure the intracellular concentration of cyclic AMP (in
picomoles per milligram of total cell protein) and summarize the results in the following table.
Which row (1 or 2) do you think corresponds to infection with V. cholerae? From these results,
does cholera toxin enter the cell in clathrin-coated vesicles?
Treatment
No drug MDC Filipin
1 1 1 1
Infection
2 400 390 15
A. Row 1; yes
B. Row 1; no
C. Row 2; yes
D. Row 2; no
