Chapter 6

What are the 3 different shapes for capsids:

1. Isometric (cubic) 2. Filamentous (helical) 3. Complex

DNA and RNA viruses are known to cause what % of cancers?

15% of human cancers

Describe the general characteristics of Viruses

> All viruses have at a minimum protein coat and nucleic acid core. - Protein coat is the capsid: protects nucleic acids + Carries required enzymes and binding proteins + Composed of protein subunits called capsomeres. - Capsid plus nucleic acids called nucleocapsid - Enveloped Viruses have a lipid bilayer membrane called an envelope. - Non- envelope (naked) viruses lack an envelope; more resistant to harsh environments.

Damage to Host Cell

Cytopathic Effects- virus- induced morphological changes to the cells visible by microscopy.

Modes of Viral Multiplication::

General Phases in animal virus multiplication cycle: 1. Adsorption- binding of virus specific molecule on host cell 2. Penetration- genome enters host cell (3 possible mechanisms*, Enveloped viruses; in bacteriophage penetration and uncoating in single step). 3. Uncoating- the viral nucleic acid is released from the capsid 4. Synthesis- viral components are produced 5. Assembly- new viral particles are constructed 6. Release- assembled viruses released by budding (expcytosis) or cell lysis (natural or artificial)

Lysogeny: The Silent Virus Infection

Lysogeny: The Silent Virus Infection > Some DNA phages are Temperate Phages that may not replicate immediately on cell entry. - So, instead the viral genome inserts into bacterial genome and becomes an inactive prophage - cell is NOT immediately lysed. - Prophage is retained and copied during normal cell division resulting in the transfer of temperature phage genome to all future host progeny, a cellular state known as lysogeny. - Induction can occur resulting in activation of the prophage followed by viral replication

Oncogenic Viruses

Mammalian Viruses capable of initiating tumors are called ___________ ________.

Lysogenic Conversion:

Phage genes in the bacterial chromosome may be active during lysogeny and can cause the production of toxins, enzymes or morphological changes that after cell phenotype- _____________ _________________. e.g: Cornyebacterium diphtheriae by phage b

Lysogeny

Prophage is retained and copied during normal cell division resulting in the transfer of temperature phage genome to all future host cell progeny, a cellular state known as ____________

Other non-cellular infectious agents

Satellite Viruses- dependent on other viruses for replication (missing some protein or enzyme) Viroids- short pieces of RNA, no protein coat; only been ID'd in plants

Transformation of the Cell :

Some animal viruses enter host cell and permanently alter its genetic material resulting in __________________ __ ____ ____` (and possibly causing cancers). - Transformed cells can divide for indefinite time periods resulting in solid tumors.

Viral Components of Viruses: Capsids, Nucleic Acids, and Envelopes.

Viral Components of Viruses are: ___________________________: > Viruses bear no resemblances to cells - Lack protein- synthesizing, no ATP made > Viruses contain only the parts needed to invade and control a host cell > Viral Particle = Core and Capsid

Fully infectious particles are called:

Virion

Viruses are obligate intracellular parasites

Viruses are _____________________________: > Viruses are simple containing at a min.: DNA or RNA (genetic material) contained within a protective protein coat (capsid) - Sub Microscopic- not visible by light microscopy -NOT CELLS, they are Inert particles: no independent metabolism, replication, & motility - Genome hijacks hosts cell metabolism - cell makes more virus - Infectious agents (microbes), not cellular organisms.

RNA viruses are:

____ ___________ are usually single stranded, a few double stranded, may be segmented into separate RNA pieces. - ssRNA genomes ready for immediate translation are positive- sense RNA - ssRNA genomes that must be converted into proper form are negative- sense RNA

ssRNA genomes that must be converted into proper form are:

________ ___________ that must be converted into proper form are Negative- sense RNA.

DNA viruses are:

_________ __________ are usually double- stranded (ds) but some are single stranded (ss)

ssRNA genomes ready for immediate translation are:

_________ ____________ ready for immediate translation are positive- sense RNA.

Describe Core Proteins:

_________ _____________ - Nucleic acid binding proteins (stabilize nucleic acid) - Preformed viral enzymes may be present within the viral core > Polymerases - DNA or RNA > Replicate's - copy RNA > Reverse transcriptase- synthesis of DNA from RNA genome (e.g. HIV virus)

Persistent Infections are:

_________ _____________ cell harbors the virus and is not immediately lysed. - Can last weeks or host's lifetime; several can periodically reactivate > Chronic Infections (productive)- some virus always made > Latent State (Non-productive) - no new virus made for long periods of time

Viroids:

_________ are short pieces of RNA, no protein coat; only been ID in plants.

Prions and Other Infectious Particles

___________ - misfolded proteins, contain NO nucleic acid - Cause transmissible spongiform encephalopathies - fatal neurodengenerative diseases. - Common in animals: > Bovine spongiform encephlapathies aka mad cow disease > Humans - Creutzfeldt - Jakob Disease Extremely resistant to usual sterilization techniques

Induction:

___________ can occur resulting in activation of the prophage followed by viral replication.

Viruses have surface proteins for:

____________ ___________ _____________ _____: attachment (receptors). - Phages have tail fibers - Many animal viruses have visible spikes (peplomers) - Allow virion to attach to specific cellular respiration.

Satelite Viruses

____________ ___________ dependent on other viruses for replication (missing some protein or enzyme)

Temperate Phages....

______________ __________ may NOT replicate immediately on cell entry

Describe Enveloped Viruses

_______________ Viruses have a Viral Envelope - Found primarily among animal viruses - Usually acquired when the virus leaves the host cell - Exposed (visible) proteins (viral receptors) projecting from the outside surface of the envelope, called spikes (peplomers), essential for attachment of the virus to the host cell.

Viral Genomes are:

________________ __________________ either DNA or RNA, NEVER both. The form of the nucleic acid is varied. - Carries genes necessary to invade host cell and redirect cell's activity to make new viruses.

Multiplication Cycle in Bacteriophages

____________________ ________ ____ _________________________ - Bacteriophages- Bacterial Viruses (phages) - Multiplication goes through similar stages as animal viruses. - Only the nucleic acid enters the cytoplasm - penetration and uncoating occur as a single step. - Release of assembled virus progeny is a result of cell lysis induced by viral enzymes (artificial lysis) - A lytic cycle is the equivalent of an acute cytocidal infection

The Viral Genome contains:

_______________________________: DNA or RNA, never BOTH. - Useful for classification (that is, DNA or RNA viruses) - Genome form: linear or circular, double or single stranded.

What is the Viral Particle structure?

___________________________________________: 1. Capsid (protein coat) - Some virus have a lipid membrane called an envelope 2. Core (Contains genetic material) - DNA or RNA - May contain viral enzymes > Some particles are defective: non- infectious > Fully infectious particles are called virions

What are the functions of the Capsid/ Envelope?

_______________________________________________: - Protects the nucleic acid when the virus is outside the host cell - Helps the virus bind to a cell surface (receptor) and assists the penetration of the viral core into a suitable host cell - Host Range largely depends on viral receptor - cellular receptor interaction.

Techniques in Cultivating and Identifying Animal Viruses

* Obligate intracellular parasites that require appropriate cells to replicate > Methods Used: - Live Animal Inoculations - occasionally used when nessecary - Bird Embryos - incubating egg is an ideal system; virus is injected through the shell. - Cell (tissue) Cultures - cultured cells grow in sheets that support viral replication and permit observation of cytopathic effect.

How are viruses classified?

- MAIN criteria used are structure, chemical composition, and genetic makeup. - Family name ends in viridae, e.g. Picornaviridae - Genus names ends in -virus, Rhinovirus (130 serotypes) - The Baltimore Classification System allows all viruses to be classified based on how the viral genome is converted to mRNA.

Detection and Treatment of Animal Viral Infections

- More difficult than other agents - Consider overall clinical relevance - Take appropriate sample > Infect cell culture- look for characteristic cytopathic effects > Screen for parts of the virus > Screen for immune response to virus (antibodies) - Antiviral drugs is limited or unavailable for most viral infections and can cause serious side effects.

Penetration and Uncoating of Viruses:

- Naked Viruses enter cells by direct penetration - Membrane Fusion and Receptor Mediated Endocytosis only possible if no cell wall is present. - Non- enveloped viruses can not enter cells by fusion.

Lysogeny results in the spread.... ?

results in the spread of the virus without killing the host cell