First Aid USMLE STEP 1: viruses
ACTUAL QUESTIONS AND CORRECT
ANSWERS
Viral structure - general features schematic - CORRECT ANSWERS✅✅
Viral recombination - CORRECT ANSWERS✅✅Exchange of genes between 2
chromosomes by crossing over within regions of significant base sequence homology.
Viral reassortment - CORRECT ANSWERS✅✅When viruses with segmented genomes
(e.g., influenza virus) exchange genetic material. For example, the 2009 novel H1N1
influenza A pandemic emerged via complex viral reassortment of genes from human, swine,
and avian viruses.
Has potential to cause antigenic shift.
Viral complementation - CORRECT ANSWERS✅✅-When 1 of 2 viruses that infect the cell
has a mutation that results in a nonfunctional protein. The nonmutated virus "complements"
the mutated one by making a functional protein that serves both viruses.
-For example, hepatitis D virus requires the presence of replicating hepatitis B virus to supply
HBsAg, the envelope protein for HDV.
Viral phenotypic mixing - CORRECT ANSWERS✅✅Occurs with simultaneous infection of
a cell with 2 viruses. Genome of virus A can be partially or completely coated (forming
pseudovirion) with the surface proteins of virus B. Type B protein coat determines the
tropism (infectivity) of the hybrid virus. However, the progeny from this infection have a
type A coat that is encoded by its type A genetic material.
Live attenuated viral vaccines vs. killed/inactive vaccines - CORRECT
ANSWERS✅✅Induce humoral and cell-mediated immunity but have reverted to virulence
on rare occasions.
Killed/inactivated vaccines induce only humoral immunity but are stable.
No booster needed for live attenuated vaccines.
,Dangerous to give live vaccines to
immunocompromised patients or their close
contacts - contacts can be vaccinated with live vaccines without risk except for polio and
ifluenza
MMR = measles, mumps, rubella; live
attenuated vaccine that can be given to HIV+ patients who do not show signs of
immunodeficiency.
Viruses with live attenuated vaccine - CORRECT ANSWERS✅✅Smallpox, yellow fever,
rotavirus, chickenpox (VZV), Sabin polio virus, MMR, Influenza (intranasal).
Killed viral vaccines - CORRECT ANSWERS✅✅Rabies, Influenza (injected), Salk Polio,
and HAV vaccines.
Killed/inactivated vaccines induce only humoral immunity but are stable.
Subunit viral vaccines - CORRECT ANSWERS✅✅HBV (antigen = HBsAg), HPV (types 6,
11, 16, and 18)
All DNA viruses except the _________ are dsDNA. - CORRECT
ANSWERS✅✅Parvoviridae (SS and linear)
All DNA viruses are linear except __________, ___________, ___________. - CORRECT
ANSWERS✅✅Papilloma-, polyoma-, and hepadnaviruses (circular)
All RNA viruses except _________ are ssRNA - CORRECT ANSWERS✅✅Reoviridae
(DS linear)
Positive-stranded RNA viruses - CORRECT ANSWERS✅✅I went to a retro (retrovirus)
toga (togavirus) party, where I drank flavored (flavivirus) Corona (coronavirus) and ate hippy
(hepevirus) California (calicivirus) pickles (picornavirus).
, Naked viral genome infectivity - CORRECT ANSWERS✅✅-Purified nucleic acids of most
dsDNA (except poxviruses and HBV) and ⊕ strand ssRNA
(≈ mRNA) viruses are infectious.
-Naked nucleic acids of ⊝ strand ssRNA and dsRNA viruses are not infectious. They require
polymerases contained in the complete virion.
All DNA viruses replicate in the ___________ except _________ . - CORRECT
ANSWERS✅✅Nucleus, poxvirus (carries own DNA-dependent RNA polymerase)
All RNA viruses replicate in the _____________ except __________ and _____________. -
CORRECT ANSWERS✅✅Cytoplasm, influenza virus, retroviruses
Naked (nonenveloped) viruses - CORRECT ANSWERS✅✅Papillomavirus, Adenovirus,
Parvovirus, Polyomavirus, Calicivirus, Picornavirus, Reovirus, and Hepevirus
Give PAPP smears and CPR to a naked Heppy (hippy).
DNA = PAPP; RNA = CPR and hepevirus.
Where does herpes viruses acquire their envelopes? What about the rest of the viruses? -
CORRECT ANSWERS✅✅Herpes gets its envelope from the nuclear membrane; the rest
get their envelope from the plasma membrane when exiting the cell
DNA viruses are the HHAPPPPy viruses - CORRECT ANSWERS✅✅Hepadna, Herpes,
Adeno, Pox, Parvo, Papilloma, Polyoma
All DNA viruses are icosahedral except for __________. - CORRECT ANSWERS✅✅Pox
(complex)
Herpesviruses virology - CORRECT ANSWERS✅✅-DNA
-Enveloped
-DS and linear
ACTUAL QUESTIONS AND CORRECT
ANSWERS
Viral structure - general features schematic - CORRECT ANSWERS✅✅
Viral recombination - CORRECT ANSWERS✅✅Exchange of genes between 2
chromosomes by crossing over within regions of significant base sequence homology.
Viral reassortment - CORRECT ANSWERS✅✅When viruses with segmented genomes
(e.g., influenza virus) exchange genetic material. For example, the 2009 novel H1N1
influenza A pandemic emerged via complex viral reassortment of genes from human, swine,
and avian viruses.
Has potential to cause antigenic shift.
Viral complementation - CORRECT ANSWERS✅✅-When 1 of 2 viruses that infect the cell
has a mutation that results in a nonfunctional protein. The nonmutated virus "complements"
the mutated one by making a functional protein that serves both viruses.
-For example, hepatitis D virus requires the presence of replicating hepatitis B virus to supply
HBsAg, the envelope protein for HDV.
Viral phenotypic mixing - CORRECT ANSWERS✅✅Occurs with simultaneous infection of
a cell with 2 viruses. Genome of virus A can be partially or completely coated (forming
pseudovirion) with the surface proteins of virus B. Type B protein coat determines the
tropism (infectivity) of the hybrid virus. However, the progeny from this infection have a
type A coat that is encoded by its type A genetic material.
Live attenuated viral vaccines vs. killed/inactive vaccines - CORRECT
ANSWERS✅✅Induce humoral and cell-mediated immunity but have reverted to virulence
on rare occasions.
Killed/inactivated vaccines induce only humoral immunity but are stable.
No booster needed for live attenuated vaccines.
,Dangerous to give live vaccines to
immunocompromised patients or their close
contacts - contacts can be vaccinated with live vaccines without risk except for polio and
ifluenza
MMR = measles, mumps, rubella; live
attenuated vaccine that can be given to HIV+ patients who do not show signs of
immunodeficiency.
Viruses with live attenuated vaccine - CORRECT ANSWERS✅✅Smallpox, yellow fever,
rotavirus, chickenpox (VZV), Sabin polio virus, MMR, Influenza (intranasal).
Killed viral vaccines - CORRECT ANSWERS✅✅Rabies, Influenza (injected), Salk Polio,
and HAV vaccines.
Killed/inactivated vaccines induce only humoral immunity but are stable.
Subunit viral vaccines - CORRECT ANSWERS✅✅HBV (antigen = HBsAg), HPV (types 6,
11, 16, and 18)
All DNA viruses except the _________ are dsDNA. - CORRECT
ANSWERS✅✅Parvoviridae (SS and linear)
All DNA viruses are linear except __________, ___________, ___________. - CORRECT
ANSWERS✅✅Papilloma-, polyoma-, and hepadnaviruses (circular)
All RNA viruses except _________ are ssRNA - CORRECT ANSWERS✅✅Reoviridae
(DS linear)
Positive-stranded RNA viruses - CORRECT ANSWERS✅✅I went to a retro (retrovirus)
toga (togavirus) party, where I drank flavored (flavivirus) Corona (coronavirus) and ate hippy
(hepevirus) California (calicivirus) pickles (picornavirus).
, Naked viral genome infectivity - CORRECT ANSWERS✅✅-Purified nucleic acids of most
dsDNA (except poxviruses and HBV) and ⊕ strand ssRNA
(≈ mRNA) viruses are infectious.
-Naked nucleic acids of ⊝ strand ssRNA and dsRNA viruses are not infectious. They require
polymerases contained in the complete virion.
All DNA viruses replicate in the ___________ except _________ . - CORRECT
ANSWERS✅✅Nucleus, poxvirus (carries own DNA-dependent RNA polymerase)
All RNA viruses replicate in the _____________ except __________ and _____________. -
CORRECT ANSWERS✅✅Cytoplasm, influenza virus, retroviruses
Naked (nonenveloped) viruses - CORRECT ANSWERS✅✅Papillomavirus, Adenovirus,
Parvovirus, Polyomavirus, Calicivirus, Picornavirus, Reovirus, and Hepevirus
Give PAPP smears and CPR to a naked Heppy (hippy).
DNA = PAPP; RNA = CPR and hepevirus.
Where does herpes viruses acquire their envelopes? What about the rest of the viruses? -
CORRECT ANSWERS✅✅Herpes gets its envelope from the nuclear membrane; the rest
get their envelope from the plasma membrane when exiting the cell
DNA viruses are the HHAPPPPy viruses - CORRECT ANSWERS✅✅Hepadna, Herpes,
Adeno, Pox, Parvo, Papilloma, Polyoma
All DNA viruses are icosahedral except for __________. - CORRECT ANSWERS✅✅Pox
(complex)
Herpesviruses virology - CORRECT ANSWERS✅✅-DNA
-Enveloped
-DS and linear
