-obligate intracellular parasites

-contain EITHER DNA or RNA (not both)

-which can be single stranded or double stranded

-can only replicate after taking control of a host cell

Positive stranded RNA virus (sense)

Negative stranded RNA nirus (anti-sense)

Retroviruses (eg. HIV)

-RNA acts like messenger RNA

-when this pos. RNA enters host cell, it immediately undergoes translation into proteins, etc

eg. polio virus

'sense' RNA makes proteins (makes 'sense')

-when the negative stranded RNA enters host cell, it must first be transcribe into positive RNA

-this requires the enzyme:

"RNA-dependent RNA polymerase"

Since humans don't have this enzyme, the viruses must carry their own

-It's RNA is transcribed into DNA

-this is done by reverse transcriptase

RNA->DNA->mRNA->Proteins, enzymes...

in the conversion of DNA to mRNA, positive strand is used for transcription, and the negative strand is ignored.

-this capsule is made up of equilateral triangles

-DNA or RNA is inside the capsule

-only ever contains RNA

-most have a spherical shape

neither icosahedral or helical

"pox in the box"

-envelope is derived from host cell membranes

naked virus - lacks envelop

enveloped viruse - is covered in an envelop

"HHAPPP"y viruses

Herpes virus

Hepadnavirus

Adenovirus

Papova virus

Parvo Virus

Pox virus (now completely irradicated)

Characteristics of DNA viruses

-not transient or labile

-many cause persistent infections

-viral genes interact with host transcriptional machinery

-usually found in the host nucleus

Single stranded

enveloped

helical capsids

replicate in cytoplasm

-usually IS labile and transient

-usually aren't persistent like DNA viruses

are an exception to RNA viruses because they have DOUBLE STRANDED RNA (dsRNA)

-are non-enveloped and include:

picornavirus - foot and and mouth disease

calcivirus - diarrhoea

reoviridae - diarrhoe

1. absorption and penetration

2.release of nucleic acid (by uncoating the virus)

3. Synthesis and assembly of the viral products

4. Release of virions from the host cell

-virus binds to host cell membrane

-part of virus binds to host cell receptors

-virus is internalized by endocytosis or fusion of the viral envelope with the host cell.

uncoats

releases a virion associatied RNA polymerase

-transcribes from negative to positive RNA

-Positive RNA undergoes transcription AND translation

-transcription/replication occur in the nucleus

-more complex than RNA replication

transcription divided into stages:

immediate early and early stages - early mRNA encodes enzymes and proteins needed for DNA replication

Late Stage - late mRNA is transcribed from progeny DNA to make structural proteins

often when the cell lyses

also can be by exocytosis

usually the virions are naked at this point. 

will get an envelop by budding through the Golgi apparatus, nucleur membrane or cytoplasmic membrane.

-cell death

-introduction of oncogenes which lead to uncontrolled growth

- latent infection (that will reappear later)

-chronic slow infection

occurs in viruses such as HIV, HPV, VZV, rabies, measles, etc

herpes go to nonreplicating neural cells OR replicating hematopoeitic lineage cells

Ex. HSV: some viruses replicated in the middle and upper layers of squamous epithelium where the inflammatory cells don't find them.

-some encode proteins to downregulate MHC class 1 expression

-viral infection induces formation of interferons

-also may trigger cytokins

-w/i 7-10 days, get specific antibodies

-after 2-3 weeks, antibodies change from IgM to IgG (can be serologically tested for increase in IgG to diagnose infection)