Page 254 - Review of Medical Microbiology and Immunology ( PDFDrive )

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mebooksfree.com mebooksfree.com mebooksfree.com viruses are made. The integrated viral DNA is called a pro- 243 mebooksfree.com
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CHAPTER 29 Replication
envelope by budding through the nuclear membrane. The
matrix protein mediates the interaction of the nucleocapsid
phage. Bacterial cells carrying a prophage can acquire new
traits, such as the ability to produce exotoxins such as diphthe-
with the envelope.
ria toxin. Transduction is the process by which viruses carry
• Lysogeny is the process by which viral DNA becomes inte-
genes from one cell to another. Lysogenic conversion is the
grated into host cell DNA, replication stops, and no progeny
term used to indicate that the cell has acquired a new trait as a
virus is made. Later, if DNA is damaged by, for example, UV
result of the integrated prophage.
light, viral DNA is excised from the host cell DNA, and progeny
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SELF-ASSESSMENT QUESTIONS
most accurate?
1. Many viruses are highly specific regarding the type of cells they
(A) During the lysogenic phase, the typical result is the production
infect. Of the following, which one is the most important determi-
of hundreds of progeny virions.
nant of this specificity?
(B) Hepatitis B virus has an RNA polymerase in the virion that is
(A) The matrix protein
required to synthesize messenger RNA from the positive strand
(B) The polymerase in the virion
of the viral DNA.
(C) The protease protein
(C) Herpesviruses have an RNA-dependent DNA polymerase in
(D) The surface glycoprotein
the virion.
(E) The viral mRNA
(D) Lysogenic conversion is the process by which bacteria acquire
2. Your summer research project is to study the viruses that cause
new genes due to transduction by a lysogenic bacteriophage.
upper respiratory tract infections. You have isolated a virus from 6. Which one of the following choices names two viruses that both
(E) Smallpox virus translates its genome into a single polypeptide,
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mebooksfree.com mebooksfree.com mebooksfree.com (A) Herpes simplex virus and human papillomavirus mebooksfree.com
a patient’s throat and find that its genome is RNA. Furthermore
which is then cleaved into structural and nonstructural
you find that the genome is the complement of viral mRNA within
proteins.
the infected cell. Of the following, which is the most appropriate
conclusion you could draw?
translate their messenger RNA into precursor polypeptides that
must be cleaved by virion-encoded proteases?
(A) The genome RNA is infectious.
(B) The genome RNA is segmented.
(C) The virion contains a polymerase.
(B) Human immunodeficiency virus and poliovirus
(D) The virion has a lipoprotein envelope.
(C) Influenza virus and measles virus
(E) A single-stranded DNA is synthesized during replication.
(D) Rabies virus and hepatitis B virus
3. The purified genome of certain viruses can enter a cell and elicit
(E) Rotavirus and parvovirus
the production of progeny viruses (i.e., the genome is infectious).
Regarding these viruses, which one of the following statements is
most accurate?
(A) Their genome RNA has positive polarity. ANSWERS
1. (D)
(B) Their genome RNA is double-stranded.
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2. (C)
(C) They have a polymerase in the virion.
3. (A)
(D) They have a segmented genome.
4. (B)
(E) They require tegument proteins in order to be infectious.
4. Regarding viral replication, which one of the following is most
6. (B)
accurate?
(A) The cytopathic effect typically occurs during the eclipse period.
PRACTICE QUESTIONS: USMLE &
(B) The early proteins are typically enzymes, whereas the late pro-
COURSE EXAMINATIONS
teins are typically capsid proteins.
(C) The assembly of a nonenveloped virus typically occurs as the
Questions on the topics discussed in this chapter can be found
virion buds from the cell membrane.
(D) Influenza viruses synthesize their mRNA using host cell-
Board) Practice Questions starting on page 720. Also see Part XIV:
encoded RNA-dependent RNA polymerase.
USMLE (National Board) Practice Examination starting on
(E) Retroviruses (e.g., HIV) synthesize their mRNA using an in the Basic Virology section of Part XIII: USMLE (National
page 751.
enzyme in the virion called reverse transcriptase.
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