Virology Flashcards
Recombination
Exchange of genes between 2 chromosomes by crossing over within regions of significant base
sequence homology.
Reassortment
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.
Phenotypic mixing
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
vaccines - type of immunity induced
Induce humoral and cell-mediated immunity
but have reverted to virulence on rare
occasions.
live attenuated vaccines - examples
Live attenuated: smallpox, yellow fever,
rotavirus, chickenpox (VZV), Sabin polio
virus, MMR, Influenza (intranasal).
“Live! One night only! See small yellow
rotating chickens get vaccinated with Sabin
and MMR! It’s incredible!”
MMR and HIV patients
MMR = measles, mumps, rubella; live
attenuated vaccine that can be given to HIV positive
patients who do not show signs of
immunodeficiency
killed vaccines – examples
Rabies, Influenza (injected), Salk Polio, and
hepatitis A vaccines.
SalK = Killed.
RIP Always.
Subunit vaccines - examples
HBV (antigen = HBsAg), HPV (types 6, 11, 16,
and 18).
DNA viruses – circular versus linear versus double-stranded
All DNA viruses except the Parvoviridae are
dsDNA.
All are linear except papilloma-, polyoma-, and
hepadnaviruses (circular).
All are dsDNA (like our cells), except “part-of-avirus”
(parvovirus) is ssDNA.
Parvus = small.
RNA viral genomes - single-stranded versus positive stranded
All RNA viruses except Reoviridae are ssRNA.
Positive-stranded RNA viruses: I went to a
retro (retrovirus) toga (togavirus) party,
where I drank flavored (flavivirus) Corona
(coronavirus) and ate hippy (hepevirus)
California (calicivirus) pickles (picornavirus).
which viruses are infectious with naked DNA?
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.
viral replication – cytoplasm versus nucleus
DNA viruses - All replicate in the nucleus (except poxvirus).
RNA viruses - All replicate in the cytoplasm (except influenza virus and retroviruses).
HHAPPPPy viruses?
Hepadna, Herpes, Adeno, Pox, Parvo,
Papilloma, Polyoma.
capsid shape in DNA virus
icosahedral, Except pox (complex).
Herpesviruses - envelope, DNA,
enveloped and linear double-stranded DNA
Hepadnavirus - envelope, DNA
envelope, circular double-stranded DNA with linear parts
adenovirus – envelope, DNA
envelope, linear double-stranded DNA
parvovirus – envelope, DNA
no envelope, linear single-stranded DNA
parvovirus – disease in children
B19 virus—aplastic crises in sickle cell disease,
“slapped cheeks” rash in children (erythema
infectiosum, or fifth disease)
RBC destruction in fetus leads to hydrops fetalis
and death
parvovirus – disease in adults
in adults leads to pure RBC aplasia and
rheumatoid arthritis–like symptoms
papilloma virus – envelope, DNA
no envelope, circular double-stranded DNA