Intro To Virology Flashcards
discovered that the agent of tobacco mosaic disease was a “contagious living fluid.”
• termed such fluid as “____” (Latin word for poison)
Martinus Beijerink
virus
- the first to isolate the tobacco mosaic virus.
• Dimitri Ivanovski
• - the smallest infectious agents
• from_____ in diameter
• contain only one kind of nucleic acid (RNA or DNA) as their genome;
• entire infectious unit termed as____
Viruses
20 to 400 nm
virion
FATHER OF VIRILOGY
→ isolated TMV by filtering the sap of diseased tobacco plants
Dimitri Ivanovski (1892)
→ first to develop the modern idea of the virus;
he referred to it as contagium vivum fluidum (soluble living germ’).
Martinus Beijerinck (1898)
• Are parasites at the genetic level, replicating only in living cells & are inert in the extracellular environment
• Rich in diversity; vary greatly in structure, genome organization and expression, and strategies of replication and transmission.
• Host range broad or extremely limited
• Infect humans, plants, animals, mycoplasmas, bacteria, algae
• Infection may have little or no effect on the host cell or may result in cell damage or death.
VIRUSES
BACTERIA
_______unicellular cells
Produce their own energy and can reproduce on their own
Size range: D and L; Larger than viruses
Can be viewed under a light microscope
Cell wall containing peptidoglycan (shapes); nucleoid, replicate by ______ (except rickettsiae and chlamydiae)
Cause bacterial infections, generally localized, treated with antibiotics
Prokaryotic
0.2 to 2.0 um in diameter & 2-8 um in length
binary fission; extracellularly
FUNGI
______cells, multicellular or microscopic unicellular
______, derive their energy source from organic matters
Larger than____
Most microscopic - 2 to 10 um
Hyphae - 5 to 50 um
____in the cell wall; require more time to grow and reproduce; reproduce asexually or sexually by___
Cause fungal infections, either localized or systemic, treated with antifungal drugs
Eukaryotic
Saprobes
bacteria
Chitin
spores
VIRUSES
______
Lack cellular structures and metabolic processes; subcellular particles
Require a____ cell to survive long-term, obtain energy, and reproduce (obligate intracellular parasites)
About_____ smaller than bacteria
Visible under an____ microscope 20 nm in diameter to 250-400 nm (human pathogens)
___capsid and___envelope; either DNA or RNA; disassemble, produce NA, proteins, then reassemble into multiple progeny viruses; faster multiplication
Cause viral infections, generally systemic, treated with antiviral medicines
Acellular
host
1000x
electron
Protein; lipoprotein
Nucleic acid core:
• either______ - encodes the genetic information necessary for replication of the virus
DNA or RNA
• Single or double stranded
• Circular or linear
• Segmented or nonsegmented
: the protein shell, or coat, that encloses the nucleic acid genome
Capsid
•: subunit of the capsid; morphologic units (polypeptides) aggregate; various arrangements are icosahedral, helical, and complex.
• Subunit: a single folded viral polypeptide chain.
Capsomeres
: capsid has a symmetrical 20-sided structure (a polyhedron) composed of equilateral triangles formed by capsomeres
• Icosahedral viruses
: a lipid bilayer that surrounds some virus particles; acquired during viral maturation by a_____process through a cellular membrane; without the envelope =_____ viruses
Envelope
budding
Naked viruses
: a viral envelope protein
• E protein
: are peplomers, virus-encoded glycoproteins (spikes) that are exposed on the surface of the envelope
• S glycoproteins
: the protein-nucleic acid complex representing the packaged form of the viral genome;
N protein
• Nucleocapsid
• Structural units: basic______ building blocks of the coat; a collection of more than one non-identical protein subunit (protomer), transfer viral NA to host cells, protect it from nucleases, structural symmetry, antigenic characteristics
protein
: viral matrix/membrane proteins, structural proteins linking the envelope with the core; called_____ in rhabdoviruses
• M protein
viral tegument
The_________ is responsible for
establishing a universal system of virus taxonomy.
As of 2017, ICTV had organized more than 4400 virus species into 122 families and 735 genera
International Committee on Taxonomy of Viruses (ICTV)
Lentivirus
Lentivirus humimdef1
Human immunodeficiency virus 1
Betacoronavirus
Betacoronavirus pandemicum
Severe acute respiratory syndrome-related coronavirus
Orthopoxvirus
Orthopoxvirus
monkeypox
Monkeypox virus
The general taxonomic hierarchy includes: OFSGS
• Order (-virales)
• Family (-viridae)
• Subfamily (-virinae)
• Genus (-virus)
• Species (-virus)
BALTIMORE CLASSIFICATION
(7)
I. dsDNA viruses
II. SSDNA viruses
III. dRNA viruses
IV. +SSRNA viruses
V. -SSRNA viruses
VI. RNA reverse transcribing viruses
VII. DNA reverse transcribing
viruses
: during replication, they use a DNA-dependent DNA polymerase to synthesize new DNA strands;
integrates into the host’s genome (via integrase enzyme);
some induce reorganization of cellular chromatin
dsDNA
: positive/plus sense single-stranded RNA virus whose genetic material is viral mRNA that encodes for proteins;
+SSRNA
can directly translate* using host cell machinery;
need to carry gene for replicase that produces the viral genomic RNA.
+ssRNA
: negative/minus sense single-stranded RNA virus whose genetic material is the antisense strand of the viral mRNA;
cannot be readily translated into viral proteins
-SSRNA
: double-stranded genomes made of RNA; serve as a template by the viral RNA-dependent RNA polymerase (RdRp) to transcribe a positive-strand RNA (mRNA)
dRNA virus
: must be transcribed first into mRNA before translation can occur; must carry RdRp (RNA replicase) to synthesize viral +ssRNA, mRNAs, & -SSRNA viral genomes;
RoRp polymerase is lacking in human cells.
-SSRNA,
dRNA,
linear,
segmented
- All DNA viruses are double stranded except
parvoviruses (SSDNA).
- All DNA viruses are icosahedral except
poxviruses (complex capsid symmetry).
- Most DNA viruses are naked. (3) are enveloped.
Herpesvirus, hepatitis B virus, and poxvirus
- Most DNA viruses contain a single genome of linear dsDNA. The _____ and _____have circular dsDNA; while _____virus consists of a single molecule of open circular partially dsDNA.
- All DNA viruses replicate in the nucleus except______
polyomavirus and papillomavirus
hepatitis B
poxviruses (cytoplasm).
RNA
Segmented genome: viral genome fragmented into 2 or more nucleic acid molecules; common in RNA viruses [segmented BOAR viruses]
a viral enzyme that catalyzes the replication of RNA from an RNA template, essential for all viruses with RNA genomes; high mutation rates;
a.k.a. RNA replicase
RNA-dependent RNA polymerase (RdRp):
: SSRNA, part of which has a positive sense and part negative; each strand has regions of + and - polarity,
ex. Arenaviridae, Bunyaviridae
Ambisense
- AlL RNA viruses replicate in the cytoplasm of the infected cell except (2)
orthomyxoviruses and retroviruses (nucleus).
. viruses are helical.
Helical viruses are usually enveloped.
All -SSRNA
- All +SSRNA viruses are icosahedral except_____&______
coronaviruses and (arteriviruses).
Most RNA viruses are enveloped.
Calicivirus, hepevirus, astrovirus, picornavirus, reovirus and picobirnavirus are naked viruses.
• Proteins
• Stable to temperature, acid, proteases, detergents, drying, ether resistant
• Released from cell by lysis
• Can dry out and retain infectivity
• Spread easily (fomites, hand to hand, dust, small droplets)
• Antibody sufficient for immunoprotection
NAKED viruses
• Membrane, lipids, proteins, glycoproteins
• Labile to acid, detergents, drying, heat, ether sensitive
• Released by budding and cell lysis
• Must stay wet
• Spread in large droplets, secretions, organ transplants, blood transfusion
• Antibody & cell mediated response; elicits hypersensitivity & inflammation
ENVELOPED viruses
• of a virion with a specific receptor site on the surface of a cell (tropism)
• Receptor molecules differ for different viruses but are generally glycoproteins
Attachment
• Virus particle is taken up inside the cell accomplished by receptor-mediated endocytosis or fusion of the virion envelope with the plasma membrane of the cell (involves a coreceptor)
Penetration or engulfment
• The physical separation of the viral nucleic acid from the other structural components of the virion; requires acidic pH in the endosome
• Infectivity of the parental virus may be lost at the uncoating stage
Uncoating (Disassembly)
Replication
•_____; essential is that specific mRNAs must be transcribed from the viral nucleic acid for successful expression and duplication of genetic information
• Some viruses carry RNA polymerases to synthesize mRNAs (negative-strand viruses, their ssRNA is complementary to mRNA (positive sense)
• Eukaryotic cells lack enzymes able to synthesize mRNA from an RNA template (RdRp)
Synthetic phase
• Newly synthesized viral genomes and capsid polypeptides assemble together to form progeny viruses
Assembly (Morphogenesis)
• Viral components are packaged and ready for release
• Generally, naked viruses accumulate in infected cells, eventually lyse and release the virus particles
• Enveloped viruses mature by a budding process (plasma membrane or other membranes in the cell).
Maturation and Release
