Acellular Agents, Ch13

Question 1

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.

Answer 1

Viruses
(L. poison) - Name proposed by Pasteur for infectious particles smaller than bacteria, also called virions or viral particles.

Question 2

Two states to viruses. One is inactive and crystalized. The other is active and infectious (alive or dead? not an organism)

Answer 2

Extracellular, virion

Intracellular

Question 3

Genetic parasites that exploits host cell’s genetic and metabolic machinery in order to propagate themselves.

Answer 3

Obligate intracellular parasites (like viruses)

Question 4

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)

Answer 4

-tropism

Question 5

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.

Answer 5

Bacteriophages

Question 6

Penetrate the host cell membranes by latching its spikes with cell receptors.

Answer 6

Animal viruses

Question 7

Transmitted cell wall abrasions or by aphids and nematodes.

Answer 7

Plant viruses and viroids

Question 8

Less known, transmitted when fungal cells fuse, no extracellular state.

Answer 8

Fungal viruses

Question 9

The size range of viruses is what?

Answer 9

Normally ultramicroscopic, between 10nm-300nm on an electron microscope (the size of the smallest bacteria, mycoplasmas.

Question 10

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?

Answer 10

Capsid
Either DNA or RNA, not both.
Nucleocapsid

Question 11

Many medically important viruses also have what in addition to capsids?

Answer 11

An phospholipid membrane envelope and sometimes enzymes

Question 12

Protein subunits that interlock to form these of distinctive shapes and configurations.

Answer 12

Capsomeres

Question 13

A type of virus in which the capsids are composed of capsomeres that bond together to form a tube around the nucleic acid.

Answer 13

Helical, rod-shaped capsomeres that form a hollow disk

Eg influenza, measles, mumps, and rabies virus.

Question 14

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.

Answer 14

Polyhedral

Icosahedral

Question 15

Viruses that have capsids of many different shapes that do not readily fit into either of the other two categories.

Answer 15

Complex
The complex shapes of many bacteriophages include isohedral heads, which contain the genome, attached to helical tails with tail fibers.

Question 16

The classification of viruses is based on what according to the International Committee on the Taxonomy of Viruses (ICTV) formed in 1966?

Answer 16

Type of nucleic acids
Presence or not of envelope
Shape and size

Question 17

The different types of genetic material that viruses can have?

Answer 17

Double-stranded DNA, dsDNA
Single-stranded DNA, ssDNA
Double-stranded RNA, dsRNA
Single-stranded RNA, ssRNA

Question 18

The genome of any particular virus may be what, as in eukaryotic or prokaryotic cells?

Answer 18

Liner and composed of several molecules of nucleic acid, like eukaryotes
Singular and circular as in most prokaryotic cells.

Question 19

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.

Answer 19

Envelope

Question 20

Virally coded proteins, which appear as spikes protruding from the surface of the envelope. They function in attachment and invasion of host cells.

Answer 20

Glycoprotein spikes

Question 21

Enveloped viruses help fusion with the host cell membrane for entry, but are susceptible to what?

Answer 21

Organic solvents, like alcohol

Detergents

Question 22

So far, taxonomists have established what for viruses?

Answer 22

Have established families for all viral genera, but only three viral orders. Family is -viridae.
No kingdoms, divisions, or classes.

Question 23

What are family and genus names for viruses?

Species and subspecies?

Answer 23

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.

Question 24

What are the five basic stages of viral replication?

Answer 24

Attachment
Entry
Synthesis
Assembly
Release

Question 25

What do enveloped viruses use for the release of infectious viral particles during replication? Nonenveloped viruses?

Answer 25

Budding | Lysis

Question 26

Replication cycle in which the phage nucleic acid takes control (usually dsDNA) and the cell undergoes lysis near the end?

Answer 26

Lytic replication | Virulent phages

Question 27

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?

Answer 27

Lysogenic replication cycle Lysogeny Used by temperate or lysogenic phages, special DNA viruses

Question 28

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.

Answer 28

Prophage

Question 29

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.

Answer 29

Induction Lytic phase Agents are UV, x-rays, carcinogens.

Question 30

When lysogenic phages change the DNA of a bacterium, for example from a harmless form into a pathogen.

Answer 30

Lysogenic conversion

Question 31

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.

Answer 31

Direct penetration

Question 32

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.

Answer 32

Membrane fusion

Question 33

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.

Answer 33

Endocytosis, engulfment

Question 34

DNA viruses typically enter what, whereas RNA viruses enter what?

Answer 34

DNA-nucleus | RNA-replicated in cytoplasm

Question 35

A human virus with a genome composed of ssDNA

Answer 35

Parvovirus

Question 36

Single-stranded viral RNA that can act directly as mRNA, which ribosome can directly translate polypeptide proteins from the codons of.

Answer 36

Positive-strand RNA, +RNA Sense strand RNA, +ssRNA RNA-dependent RNA polymerase (eg poliovirus)

Question 37

A complementary strand transcribed from the +ssRNA genome by viral RNA polymerase. Serves as a template for the transcription of multiple +ssRNA genomes.

Answer 37

Negative-strand RNA, -RNA Antisense genome, -ssRNA Packaged with viral Rna polymerase (eg rabies)

Question 38

+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.

Answer 38

Retroviruses | ssRNA genome into dsDNA which enters the nucleus and becomes lysogenic forming a provirus or transcribed into new ssRNA.

Question 39

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.

Answer 39

dsRNA viruses Parent strand remains intact and the progeny RNA molecule is completely new, conservative replication. Copy of a copy, eg retroviruses.

Question 40

When animal viruses remain dormant in cells. It may prolonged for years with no viral activity, signs, or symptoms. The viral incorporation is permanent.

Answer 40

Latency | Latent viruses, proviruses

Question 41

Diagnosis by signs and symptoms. Some are typical while others show multiple manifestations. Others mimic other infections.

Answer 41

Clinical

Question 42

Diagnosis by examination (LM)- affected tissues for inclusion bodies (e.g. Negri bodies in rabies)

Answer 42

Microscopic

Question 43

Diagnosis by examination (TEM) –electron microscopy (shadow casting –> gold dust and negative staining using heavy metals like OsO4)

Answer 43

Ultramicroscopic

Question 44

Diagnosis by testing for antibodies. Titers taken at onset and peak of infection (4-fold rise in titer = active infection).

Answer 44

Serologic

Question 45

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)

Answer 45

Antigen detection techniques

Question 46

Diagnosis by looking for cytopathogenic effects (CPE) for animal viruses on monolayers, or plaques in the case of bacteriophages.

Answer 46

Cell culture techniques

Question 47

For propagation of viruses for vaccine production. Inexpensive, among the largest of cells, free of contamination, and self-scuffient nourishment.

Answer 47

Embyronated eggs

Question 48

Nucleic acid analysis that detects and amplifies even minute amounts of DNA or RN. Very sensitive but background problems.

Answer 48

Polymerase chain reaction

Question 49

Nucleic acid analysis that uses DNA segments to detect common sequences of viruses.

Answer 49

Gene probes

Question 50

Areas on a cell culture of a virus where the phages have lysed the bacteria.

Answer 50

Plaques | Plaque assays are where eat plaque corresponds to a single phage in the original bacterium-virus mixture.

Question 51

Extremely small, circular pieces of ssRNA without capsids that are infectious and pathogenic in plants.

Answer 51

Viroids Cadang disease in coconuts Viroidlike agents infect some fungi but not plants.

Question 52

This virus is latent in nerve cells, with an eruption later triggered by changes.

Answer 52

Herpes simplex virus-fever blisters and genital herpes. | Herpes zoster virus-chickenpox and shingles.

Question 53

Proteinaceous agent that lacked instructional nucleic acid. Clumps of their beta-pleated PrPsc encourage cellular PrPc to refolding into PrPsc.

Answer 53

Prions Nine animal diseases. Mad cow disease in people, causing spongiform encephalopathy. May be linked to some genetic diseases.

Question 54

Slow viral infection that usually lasts months or years. It's usually fatal. Examples?

Answer 54

Persistent viral infection HIV-dementia results from brain degeneration. Measles-encephalitis causing mental deterioration

Question 55

Gross changes in the cell | Compacted masses of viruses or damaged cell organelles.

Answer 55

Cytopathogenic effects | Inclusion bodies

Question 56

Cell transformation causing cancer. 10% of all cancers.

Answer 56

Oncogenic viral effects | HPV and liver cancer