VIRUSES AND PRIONS

Virome

the entire population of viruses associated with the human body

Bacteriophages

viruses that infect bacteria

Capsid

shell; surround the nucleic acid in the central core.

Nucleocapsid

Capsid and the nucleic acid

Envelope

modified piece of host cell membrane

Naked Viruses

viruses that consist of only a nucleocapsid

Spikes

molecules that allow viruses to dock with their host cells.

Virion

A fully formed virus that is able to establish an infection in a host cell

Capsomeres

identical protein subunits that spontaneously self assemble to form the capsid

Helical Capsids

rod-shaped capsomeres that bond together to form a series of hollow discs resembling a bracelet

naked helical virus

Nucleocapsid is rigid and tightly wound into a cylinder-shaped package

Tobacco mosaic virus

Example of a naked helical virus.

Enveloped helical nucleocapsids

more flexible and tend to be arranged as a looser helix within the envelope.

Influenza, measles, and rabies

Examples of enveloped helical nucleocapsid

Icosahedron

Three-dimensional, 20-sided figure with 12 evenly spaced corners

32

How many capsomeres does poliovirus have?

252

How many capsomeres does poliovirus have?

Complex Capsids

found in bacteriophage; have multiple types of proteins; take shapes that are not symmetrical

Genome

sum total of the genetic information carried by any organism

Adenovirus

example of a naked icosahedral virus.

Hepatitis B Virus and herpes simplex virus

example of a enveloped icosahedral virus

Positive-sense RNA

Single-stranded RNA genomes ready for immediate translation into proteins

Negative-sense RNA

RNA genomes that need to be converted into the proper form to be made into proteins

Segmented RNA

individual genes exist on separate pieces of RNA

Influenza

examples of a segmented RNA

Polymerases

synthesize DNA and RNA

Replicases

copy RNA

reverse transcriptase

synthesizes DNA from RNA

HIV

A virus that comes equipped with reverse transcriptase

International Committee on the Taxonomy of Viruses

Meaning of ICTV

59 orders and 189 families

How many orders and families are there based on ICTV

-virales

Naming of virus orders

-viridae

Naming of virus families

-virus

Naming of virus genera

Adsorption

Penetration

Uncoating

Synthesis

Assembly

Release

General phases in the multiplication cycle of animal viruses

Adsorption

The virus attaches to its host cell by specific binding of its spikes to cell receptors.

Penetration

The virus is engulfed into a vesicle and its envelope is uncoated

Uncoating

freeing the viral RNA into the cell cytoplasm

Synthesis: Replication and Protein Production

Under the control of viral genes, the cell synthesizes the basic components of new viruses: RNA molecules, capsomeres, spikes.

Assembly

Viral spike proteins are inserted into the cell membrane for the viral envelope; nucleocapsid is formed from RNA and capsomeres

Release

Enveloped viruses bud off to the membrane, carrying away an envelope with the spikes. This complete virus or virion is ready to infect another cell.

8 hours

Length of the entire multiplication cycle in polioviruses

72 hours

Length of the entire multiplication cycle in some herpesviruses

Host range

The limited range of host cells that each type of virus can infect and parasitize.

Poliovirus

infects both intestinal cells and nerve cells of primates (humans, apes, and monkeys) is considered moderately restrictive

Rabies virus

considered to be minimally restricted because it can infect various cells of all mammals

Tropisms

specificities of viruses for certain tissues

Endocytosis

entire virus is engulfed by the cell and enclosed in a vacuole or vesicle

Make new genomic material and new proteins

Two main jobs of the virus upon entering its host cell

DNA viruses (except poxviruses)

Enter the host cell's nucleus and are replicated and assembled there

RNA viruses (except retroviruses)

Replicated and assembled in the cytoplasm

Budding or exocytosis

How are enveloped viruses liberated

Cytopathic effects

virus-induced damage to the cell that alters its microscopic appearance

Inclusion bodies

compacted masses of viruses or damaged cell organelles in the nucleus and cytoplasm

Syncytia

fusion of multiple host cells into single large cells containing multiple nuclei

Persistent infections

last from a few weeks to the remainder of the host's life

Provirus

viral DNA is incorporated into the DNA of the host

Oncoviruses

animal viruses that enter their host cell and permanently alter its genetic material, which can lead to cancer.

Transformation

Effect of oncoviruses on the cell

1915

When bacterial viruses were first discovered

Temperate phages

can participate in a lytic phase, but they also have the ability to undergo adsorption and penetration into the bacterial host and then not undergo replication or release immediately.

Prophage stage

insertion into the bacterial chromosome and results in a condition called lysogeny

Lysogeny

Bacterial chromosome carries bacteriophage DNA.

Induction

prophage in a lysogenic cell becomes activated and progresses directly into viral replication and the lytic cycle

Virophage

a virus that parasitize other viruses

Lysogenic conversion

A bacterium acquires a new trait from its temperate phage.

In vivo methods

Methods that use living embryos or animals

In Vitro Methods

Use cells or tissues that are cultivated in the lab

Primary purposes of viral cultivation

- to isolate and identify viruses in clinical specimens

- to prepare viruses for vaccines

- to do detailed research on viral structure, multiplication cycles, genetics, and effects on host cells.

Plaques

virus-infected cells have been destroyed show up as clear, well-defined patches in the cell sheet

Interferon

naturally occurring human cell product, can also be used with some success in treating and preventing viral infections.

Prions

- deposition of distinct protein fibrils in the brain tissue

- these fibrils are the agents of the disease

Creutzfeldt-Jakob disease (CJD)

afflicts the central nervous system and causes gradual degeneration and death.

Bovine spongiform encephalopathy

mad cow disease; disease could be acquired by human who consumed contaminated beef.

Satellite Viruses

dependent on other viruses for replication

Viroids

small circular RNA molecules that infect plants and disrupt their growth

Adeno-associated virus (AAV)

Example of satellite viruses