Acellular Agents, Ch13 Flashcards
A miniscule acellular infectious agent having one or several pieces of nucleic acid, either DNA or RNA. The nucleic acid is the genome. Also lacks cytosol and functional organelles.
Viruses
(L. poison) - Name proposed by Pasteur for infectious particles smaller than bacteria, also called virions or viral particles.
Two states to viruses. One is inactive and crystalized. The other is active and infectious (alive or dead? not an organism)
Extracellular, virion
Intracellular
Genetic parasites that exploits host cell’s genetic and metabolic machinery in order to propagate themselves.
Obligate intracellular parasites (like viruses)
Host range is usually very specific. Viral glycoproteins attach to specific receptor sites on host cell membranes (some are known to parasitize all types of cells)
-tropism
Infect by attaching to the cell wall or flagella or fimbriae of bacteria. Complex structure with an icosahedral cubical head, a helical tail, and fibers for attachment.
Bacteriophages
Penetrate the host cell membranes by latching its spikes with cell receptors.
Animal viruses
Transmitted cell wall abrasions or by aphids and nematodes.
Plant viruses and viroids
Less known, transmitted when fungal cells fuse, no extracellular state.
Fungal viruses
The size range of viruses is what?
Normally ultramicroscopic, between 10nm-300nm on an electron microscope (the size of the smallest bacteria, mycoplasmas.
The protein coat of a virus that surrounds the genome (which is made of what?), used for protection and host cell attachment. What are both the coat and the genome together called?
Capsid
Either DNA or RNA, not both.
Nucleocapsid
Many medically important viruses also have what in addition to capsids?
An phospholipid membrane envelope and sometimes enzymes
Protein subunits that interlock to form these of distinctive shapes and configurations.
Capsomeres
A type of virus in which the capsids are composed of capsomeres that bond together to form a tube around the nucleic acid.
Helical, rod-shaped capsomeres that form a hollow disk
Eg influenza, measles, mumps, and rabies virus.
A type of virus in which the capsids are roughly spherical, with a shape like a dome. The most common type is this, with 20 triangular faces and 12 corners.
Polyhedral
Icosahedral
Viruses that have capsids of many different shapes that do not readily fit into either of the other two categories.
Complex
The complex shapes of many bacteriophages include isohedral heads, which contain the genome, attached to helical tails with tail fibers.
The classification of viruses is based on what according to the International Committee on the Taxonomy of Viruses (ICTV) formed in 1966?
Type of nucleic acids
Presence or not of envelope
Shape and size
The different types of genetic material that viruses can have?
Double-stranded DNA, dsDNA
Single-stranded DNA, ssDNA
Double-stranded RNA, dsRNA
Single-stranded RNA, ssRNA
The genome of any particular virus may be what, as in eukaryotic or prokaryotic cells?
Liner and composed of several molecules of nucleic acid, like eukaryotes
Singular and circular as in most prokaryotic cells.
A portion of the membrane system of a host cell, composed of a phospholipid bilayer and proteins. Some proteins are bound to the capsid, others are glycoproteins.
Envelope
Virally coded proteins, which appear as spikes protruding from the surface of the envelope. They function in attachment and invasion of host cells.
Glycoprotein spikes
Enveloped viruses help fusion with the host cell membrane for entry, but are susceptible to what?
Organic solvents, like alcohol
Detergents
So far, taxonomists have established what for viruses?
Have established families for all viral genera, but only three viral orders. Family is -viridae.
No kingdoms, divisions, or classes.
What are family and genus names for viruses?
Species and subspecies?
Family is -viridae.
Suffix “virus” used for genus name that is italicized.
Species names not latinized, but instead use common english designations, followed by a number for a subspecies.
What are the five basic stages of viral replication?
Attachment Entry Synthesis Assembly Release
What do enveloped viruses use for the release of infectious viral particles during replication? Nonenveloped viruses?
Budding
Lysis
Replication cycle in which the phage nucleic acid takes control (usually dsDNA) and the cell undergoes lysis near the end?
Lytic replication
Virulent phages
Modified replication cycle of some bacteriophages in which the infected host cell’s chromosomes replicate together with the prophage for many generations before they lyse?
Lysogenic replication cycle
Lysogeny
Used by temperate or lysogenic phages, special DNA viruses
Inactive bacteriophage that codes a protein that surpasses its genes. Inserted into the DNA of the bacterium, becoming a physical part of the bacterial chromosome in lysogeny.
Prophage
The process whereby a prophage us excised from the host chromosome. Agents of this are usually the same physical and chemical agents that damage DNA molecules.
Induction
Lytic phase
Agents are UV, x-rays, carcinogens.
When lysogenic phages change the DNA of a bacterium, for example from a harmless form into a pathogen.
Lysogenic conversion
A process by which an animal viral capsid attaches and sinks into the cytoplasmic membrane, creating a pore through which the genome alone enters the cell.
Direct penetration
A penetration method of animal viruses in which the entire capsid and its contents (including genome) enter the host cell by fusing with the plasma membrane and releasing into the cytoplasm.
Membrane fusion
A penetration method of animal viruses in which the entire capsid and its contents (including genome) by attaching to the receptor molecules on the cell’s surface, stimulating it to do this.
Endocytosis, engulfment
DNA viruses typically enter what, whereas RNA viruses enter what?
DNA-nucleus
RNA-replicated in cytoplasm
A human virus with a genome composed of ssDNA
Parvovirus
Single-stranded viral RNA that can act directly as mRNA, which ribosome can directly translate polypeptide proteins from the codons of.
Positive-strand RNA, +RNA
Sense strand RNA, +ssRNA
RNA-dependent RNA polymerase (eg poliovirus)
A complementary strand transcribed from the +ssRNA genome by viral RNA polymerase. Serves as a template for the transcription of multiple +ssRNA genomes.
Negative-strand RNA, -RNA
Antisense genome, -ssRNA
Packaged with viral Rna polymerase (eg rabies)
+ssRNA viruses that do not use their genome as mRNA, but instead use a DNA intermediary transcribed from +RNA by reverse transcriptionase carried within the capsid.
Retroviruses
ssRNA genome into dsDNA which enters the nucleus and becomes lysogenic forming a provirus or transcribed into new ssRNA.
Virus where the positive strand serves as mRNA for the translation of proteins, one of which is an RNA polymerase that transcribes it. Each strand of RNA acts as a template for its opposite.
dsRNA viruses
Parent strand remains intact and the progeny RNA molecule is completely new, conservative replication. Copy of a copy, eg retroviruses.
When animal viruses remain dormant in cells. It may prolonged for years with no viral activity, signs, or symptoms. The viral incorporation is permanent.
Latency
Latent viruses, proviruses
Diagnosis by signs and symptoms. Some are typical while others show multiple manifestations. Others mimic other infections.
Clinical
Diagnosis by examination (LM)- affected tissues for inclusion bodies (e.g. Negri bodies in rabies)
Microscopic
Diagnosis by examination (TEM) –electron microscopy (shadow casting –> gold dust and negative staining using heavy metals like OsO4)
Ultramicroscopic
Diagnosis by testing for antibodies. Titers taken at onset and peak of infection (4-fold rise in titer = active infection).
Serologic
Diagnosis techniques – quick screening but problems with false positive and false negatives. Use monoclonal antibodies to improve these techniques (e.g. ELISA and latex agglutination tests)
Antigen detection techniques
Diagnosis by looking for cytopathogenic effects (CPE) for animal viruses on monolayers, or plaques in the case of bacteriophages.
Cell culture techniques
For propagation of viruses for vaccine production. Inexpensive, among the largest of cells, free of contamination, and self-scuffient nourishment.
Embyronated eggs
Nucleic acid analysis that detects and amplifies even minute amounts of DNA or RN. Very sensitive but background problems.
Polymerase chain reaction
Nucleic acid analysis that uses DNA segments to detect common sequences of viruses.
Gene probes
Areas on a cell culture of a virus where the phages have lysed the bacteria.
Plaques
Plaque assays are where eat plaque corresponds to a single phage in the original bacterium-virus mixture.
Extremely small, circular pieces of ssRNA without capsids that are infectious and pathogenic in plants.
Viroids
Cadang disease in coconuts
Viroidlike agents infect some fungi but not plants.
This virus is latent in nerve cells, with an eruption later triggered by changes.
Herpes simplex virus-fever blisters and genital herpes.
Herpes zoster virus-chickenpox and shingles.
Proteinaceous agent that lacked instructional nucleic acid. Clumps of their beta-pleated PrPsc encourage cellular PrPc to refolding into PrPsc.
Prions
Nine animal diseases. Mad cow disease in people, causing spongiform encephalopathy. May be linked to some genetic diseases.
Slow viral infection that usually lasts months or years. It’s usually fatal. Examples?
Persistent viral infection
HIV-dementia results from brain degeneration.
Measles-encephalitis causing mental deterioration
Gross changes in the cell
Compacted masses of viruses or damaged cell organelles.
Cytopathogenic effects
Inclusion bodies
Cell transformation causing cancer. 10% of all cancers.
Oncogenic viral effects
HPV and liver cancer
