Viruses are composed of
Nucleic acid and protein
Protein coat is called a
Capsid
Host range
The spectrum of cells that a virus can infect
Determined by specific attachment of virus spike proteins to receptors on a cell's surface and ability of the host cell to support viral replication
Viral families
Based on nucleic acid type, replication strategy and morphology
Viral species
A group of viruses with the same structure, genetic information and host range
Cell culture
Preferred method of propagating viruses
Cytopathic effect
The virus titer (amount of virus) is often determined by observing the lysis of cells
Viral cultivation
Some viruses are not easily cultivated in cell culture or embryonated eggs
Serological method
Antibody-based
Propagation method
Used where study is needed on cell culture
PCR method
DNA-based method
Stages of virus "life" cycle
1. Attachment: Virus spike proteins attach to a cell membrane receptor
2. Entry: The virion enters by endocytosis or membrane fusion
3. Uncoating: The viral RNA or DNA is released from the capsid
4. Biosynthesis: Viral nucleic acid and proteins are produc
Early genes
Code for enzymes involved in inactivation of host cell processed and initiation of viral DNA replication
(Expressed)
Late genes
Code for capsid and assembly proteins
(Transcribed)
Viral RNA polymerase
Used to make more copies of the viral genome
Acute infection
Viral multiplication occurs and symptoms are unseen - usually followed by recovery without recurrence
Persistent Infection
Latent infection: Virus is present but is not active or has periods of inactivity
Chronic infection: Virus reproduction causes symptoms after a long period of infection
Viral transformation
When a virus-infected cell becomes cancerous
Oncogenic virus
Viruses capable of causing cancer
Prion
Infective protein
-No nucleic acid
-NOT A VIRUS
-Associated with neurological diseases
-Causes destruction of brain tissue
PrPc (PrPsens)
Normal cell surface glycoprotein though to be important in synaptic development
PrPsc (PrPres)
Identical to PrPc on the primary level (amino acid sequence) but different on the secondary level
Aggregates within brain cells and form "amyloid" plaques: deposit consisting of insoluble protein that results from the degeneration of tissue
PrPsc
Reacts with PrPc and causes PrPc to change form