3.1, 3.2 Virology Basics Flashcards
A virus is an infectious __________________ parasite comprising ___________ surrounded by a ___________ and/or an __________ derived from a host __________________.
obligate intracellular; genetic material (DNA or RNA); protein coat; envelope; cell membrane
what protects the viral nucleic acid genome
protein coat
How do viruses replicate
inside host cells
All viruses must make __________, to be translated by ____________
mRNA; host ribosomes
T/F viruses are dependent on the infected cell ribosomes to synthesize viral proteins
T; this is partly why they are obligate intracellular parasites
T/F viruses can use the host cell to provide energy for replication, or they can use their own energy sources
F; they are absolutely dependent on the host to provide energy
Viruses are ABSOLUTELY DEPENDENT on the host for what (2)
1) ribosomes to translate their viral mRNA into viral proteins
2) energy for viral replication
What is the difference between virus and virion
Virus is a broad term to describe the viral particles in any stages, as well as the nucleic acids and proteins; virion refers exclusively to the physical particle in its extra-cellular phase
what are 2 similarities between viruses and bacteria
1) both have either DNA or RNA (bacteria have both)
2) both CAN be obligate intracellular pathogens (all viruses and some bacteria)
T/F you can see viral particles with a light microscope
F; however, you can see cytoplasmic or nuclear aggregates of viral particles/nucleic acids on light microscopy
what are the 4 basic components of viruses
1) viral genome (DNA or RNA)
2) proteins (structural or non-structural)
3) lipids (form the envelope of some viruses)
4) carbohydrates (glycolipids or glycoproteins)
what are 4 ways to CLASSIFY viruses
1) nature and sequence of nucleic acid
2) diameter or shape
3) symmetry of protein shell
4) presence or absence of lipid envelope
what 3 terms can be used to describe the symmetry of a viral protein shell
icosahedral, helical, complex
what is the outermost surface of a non-enveloped virus
the capsid
what is the outermost surface of an enveloped virus? what does it contain?
lipid bilayer envelope; contains viral glycoproteins
are enveloped or non-enveloped viruses more stable outside the host
non-enveloped
T/F non-enveloped (naked) viruses are rapidly inactivated by solvents, detergents, and bile salts
F; enveloped viruses are
are most enteric animal viruses enveloped or non-enveloped
enveloped
what are the consequences of asymptomatic or subclinical viral infections
persistent infection, immunity or recovery
what are the consequences of acute viral infection/disease
death, recovery or persistent infection
what are the consequences of chronic viral infection/disease
recurrent clinical disease or persistent infection
what are the stages of viral replication
1) recognition
2) attachment
3) penetration
4) uncoating
5) mRNA synthesis
6) protein synthesis
7) genome replication
8) assembly
9) lysis and release (naked) OR budding and release (enveloped)
what influences tissue tropism for viral infection
presence of cellular receptors that permit entry of the virus
what explains species susceptibility to viruses
animal species express different cell surface receptors
receptors can be (4)
proteins, glycoproteins, carbohydrates or lipids
what often determines the mechanism of virus entry into the cell
the nature of the receptor
describe the lock and key fashion of viral entry into host cells
viral proteins/glycoproteins interact with host receptors/co-receptors
what are the 3 methods of viral entry into a cell
1) direct penetration
2) receptor-mediated endocytosis
3) fusion
what virus types enter a cell by receptor-mediated endocytosis
all non-enveloped and some enveloped
what virus types enter a cell by fusion
enveloped viruses
what mediates fusion
1+ virion surface glycoproteins
on what two membranes can fusion occur
PM or endosomal membrane
T/F fusion proteins can be native fusion competent or require a conformational change
T
what is the fusion peptide made of
hydrophobic amino acids
fusion allows the creation of a ____________ that facilitates release of viral ____________ into the cytoplasm
fusion pore; nucleocapsids
what is uncoating
when the virus genome separates from the capsid proteins
with few exceptions, RNA viruses uncoat in the ____________ and DNA viruses uncoat in the ___________
cytoplasm; nucleus
genome replication is needed to produce (2)
mRNA for translation of proteins and a genome copy for the progeny virus
what is unique about - sense RNA virus polymerases
they encode RNA dependent RNA polymerase
what type of viruses require RNA dependent RNA polymerase
negative sense RNA viruses
T/F DNA viruses use cellular polymerases to replicate their genome
T
assembly takes place through __________ and ___________ interactions
protein-protein; protein-genome
T/F assembly can take place as a separate or concurrent step to release
T
what are inclusion bodies
sites of viral multiplication in an infected cell; aggregates of replication intermediates
T/F inclusion bodies can be in the cytoplasm or the nucleus
T
do RNA or DNA viruses have higher mutation rates
RNA
mutations are responsible for
antigenic drift
reassortment of segmented genomes is responsible for
antigenic shift
what types of viruses can undergo antigenic shift
segmented RNA viruses
viral pathogenesis involves (4)
1) entry
2) replication
3) lesions in organs affected
4) dissemination to the next host
what is the incubation period
part of infection where you are asymptomatic; before clinical disease
transmission of a virus depends on the nature of (2)
1) virus
2) host
what are the 5 ways that viruses result in disease
1) tissue/cell damage
2) inflammation
3) transformation
4) secondary bacterial infection
5) immunosuppression
what are the best types of vaccines
RNA vaccines
what are some potential targets of antivirals
virus-encoded enzymes; processes critical to viral replication
T/F an antiviral is ok as long as it blocks replication slightly
F; must block completely or resistance
when should you give an antiviral
immediately after infection or appearance of clinical signs
T/F antivirals are uncommon in food animal medicine
T
what is characteristic of cytopathic effect (4)
1) rounding/clumping of cells
2) fusion of cells
3) syncytia (giant cells)
4) vacuolation
