Chapter 6: An Introduction to Viruses

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Viruses

-noncellular particles with a definite size, shape, and chemical composition

Viruses are considered the most ____ ____ on Earth.

-abundant microbes

Viruses played a role in evolution of ____, ____and____.

-Bacteria, Archea and Eukarya.

Viruses are ________that cannot multiply unless it invades a specific host cell.

-obligate intercellular parasite

Viruses bear no resemblance to____.

-cells

Viruses lack _____ found even in the simplest cells

-protein-synthesizing machinery

Viruses contain only the parts needed to_________.

-Invade and control a host cell.

All viruses have capsids - protein coats that enclose and protect their______.

-nucleic acids.

The capsid together with the nucleic acid are_____.

-nucleocapsid.

Some viruses have an external covering called____.

-envelope

Viruses without an envelope are considered ____.

-naked.

Each capsid is constructed from identical subunits called capsomers made of______.

-protein

Two general structural types of viruses:

-Helical (continuous helix of capsomers forming a cylindrical nucleocapsid)
-Icosahedral (20-sided with 12 corners)

Viral envelope-Mostly____viruses.

-animal

Viral envelope-aquired when the virus leaves the___.

-host cell

Viral envelope-exposed proteins on the outside called ____, essential for ____ of the virus to the___.

-spikes
-attatchment
-host cell

Functions of Capsid/Envelope-Protects the ____ when the virus is outside the host cell.

-nucleic acid

Functions of Capsid/Envelope-Helps the virus to bind to a ____ and assists the ____ of the viral DNA or RNA into a suitable host cell

-cell surface
-penetration

Complex viruses: atypical viruses-Poxviruses lack a typical ___ and are covered by a dense layer of ___.

-capsid
-lipoproteins

Complex viruses: atypical viruses-Some ____ have a polyhedral nucleocapsid along with a helical tail and ____.

-bacteriophages
-attachment fibers

genome

-the sum total of genetic information carried by an organism.

viruses contain either DNA or RNA but ______.

-never both

Viruses possess only the genes necessary to ____ host cell and redirect cell's activity to make ____.

-invade
-new viruses

DNA viruses - Usually ____ but may be single stranded (ss)

-double stranded (ds)

RNA viruses -Usually ____, may be double stranded, may be segmented into separate ____.

-single stranded (ss)
-RNA pieces

*RNA viruses -ssRNA genomes ready for immediate translation into proteins are called ____.

-positive-strand RNA.

*RNA viruses -RNA genomes that have been converted into proper form are ____.

-negative-strand RNA.

General phases in animal virus multiplication cycle:

Adsorption -Penetration -Uncoating -Synthesis -Assembly -Release
**Arnolds Pig Ulyssess Sits and Reads**

Adsorption

- binding of virus to specific molecule on host cell

Penetration

- genome enters host cell

Uncoating

- the viral nucleic acid is released from the capsid

Synthesis

- viral components are produced.

Assembly

- new viral particles are constructed.

Release

- assembled viruses are released by budding (exocytosis) or cell lysis.

Adsorption and Host Range-Virus coincidentally collides with a susceptible host cell and adsorbs specifically to_______________.

-receptor sites on cell membrane.

Adsorption and Host Range-Spectrum of cells a virus can infect - _________.

-host cell.

Spectrum of cells a virus can infect.
Hepatitis B -

-human liver cells.

Spectrum of cells a virus can infect.
Poliovirus -

-primate intestinal and nerve cells.

Spectrum of cells a virus can infect.
Rabies -

-various cells of many mammals.

Penetration/Uncoating-Flexible cell membrane is penetrated by the whole virus or its nucleic acid by:

-Endocytosis
-Fusion

Replication and Protein Production
Varies depending on whether the virus is a_____.

-DNA or RNA viruse

Replication and Protein Production
DNA viruses generally are replicated and assembled in the____.

-Nucleus

Replication and Protein Production
RNA viruses generally are replicated and assembled in the____.

-Cytoplasm

Replication and Protein Production
Positive-sense RNA contain the message for____.

-translation.

Replication and Protein Production
Negative-sense RNA must be converted into____.

-Positive-sense message.

Damage to Host Cell
Cytopathic effects --virus induced damage to cells.

1.Changes in size and shape.
2. Cytoplasmic inclusion bodies
3. Inclusion bodies
4. Cells fuse to form multinucleated cells
5. cell lysis
6. Alter DNA
7. Transform cells into cancerous cells.

Persistent infections

- cell harbors the virus and is not immediately.

Bacteriophages

-Bacterial viruses (Phages)

6 Steps in Phage Replication

1.Adsorption
2.Penetration
3.Replication
4.Assembly
5.Maturation
6.Release

Lysogeny

-The Silent Virus Infection; does not kill the host cell.

Prions

-misfolded proteins, contain no nucletic acids.

Virods

-short pieces of RNA, no protein coat; only been identified in plants.

A virus is a tiny infectious____.

-particle

Viruses are known to infect____.

-all organisms.

The capsid is composed of protein subunits called____.

-capsomers

The envelope of an animal virus is derived from the ____ of its host cell.

-membrane

The nucleic acid of a virus is ____.

-either DNA or RNA.

The general steps in viral multiplication cycle are:

Absorption,Penetration,Synthesis,Assembly,and Release.

A prophage is a ____stage in the cycle of ____.

-latent
-bacterial viruses

The nucleic acid of animal viruses enters the host cell through____.

-fusion and endocytosis

In general, RNA viruses multiply in the cell ____, and DNA viruses multiply in the cell____.

-cytoplasm
-nucleus

Enveloped viruses carry surface receptors called __.

-spikes.

Viruses that persist in the cell and cause recurrent disease are considered____.

-latent

Viruses cannot be cultivated in ____.

-blood algar

Clear patches in cell cultures that indicate sites of virus infection are called____.

-plagues

Which of these is not a general pattern of virus morphology? -enveloped,helical. -naked,icosahedral -enveloped, icosahedral -complex,helical.

-complex,helical.

Circle the viral infections from this list: Cholera, Rabies, Plaque, Cold sores, Whooping cough, Tetanus, Genital warts, Gonorrhea, Mumps, Rocky Mountain spotted fever, Syphilis, Rubella, Rat bite fever.

Rabies,Cold sores, Genital warts, Mumps, Rubella.

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