Viruses, Viroids And Prions Flashcards
(18 cards)
What are the characteristics of viruses?
Viruses can replicate and evolve but do not grow, lack genes for energy production and protein synthesis, contain DNA or RNA (not both), are insensitive to environmental changes, can only reproduce inside a living cell, affect all domains of life, and are usually very small.
Examples of viruses include those that cause AIDS, Ebola, and Covid-19.
What is the general structure of a virus?
A protein coat (capsid) surrounding a nucleic acid genome that may be:
* Double stranded DNA
* Single stranded DNA
* Double stranded RNA
* Single stranded RNA
A virus may be naked or enveloped.
What is the difference between naked and enveloped viruses?
In a naked virus, the outer layer is the protein coat or capsid. In an enveloped virus, the protein layer is surrounded by a lipid bilayer membrane acquired from the host cell.
What are the types of viral genomes?
Viral genomes may include:
* Double stranded DNA (e.g., herpes complex virus-1)
* Single stranded DNA (e.g., bacteriophage M13)
* Double stranded RNA (e.g., rotavirus)
* Single stranded RNA (e.g., SARS-Cov-2)
What is the generic life cycle of a virus with a DNA genome?
- Entry and coating into host cell
- Viral DNA replication, viral mRNA replication to create capsid proteins
- Self-assembly of new virus particles and exit from the cell.
How do (+)ss RNA viruses replicate?
- Viral RNA (+) strand is present
- RNA-dependent RNA polymerase synthesizes RNA complementary to the viral genome (-) strand
- RNA-dependent RNA polymerase uses (-) strand as a template to synthesize new copies of the virus genome
- Assembly of new virus particles.
What is a viroid?
An infectious agent without protein, consisting of a circular, single stranded RNA molecule that replicates inside infected cells.
What is the Potato spindle tuber viroid?
A viroid that affects the growth of potatoes, tomatoes, and peppers, consisting of a circular, single stranded RNA molecule about 350 nucleotides long with substantial internal base pairing.
What are prions?
Infectious agents without DNA or RNA that cause transmissible spongiform encephalopathies (TSEs), leading to fatal neurological deterioration.
What diseases are caused by prions?
Examples of prion diseases include:
* Creutzfeldt-Jakob disease
* Variant Creutzfeldt-Jakob disease
* Fatal familial insomnia.
How do normal and misfolded prion proteins differ?
Normal prion protein is protease sensitive, has high a-helix content (42%), low b-sheet content (3%), is soluble, and does not form aggregates. Misfolded prion protein is protease resistant, has low a-helix content (30%), high b-sheet content (43%), is insoluble, and aggregates to form fibers.
What are the characteristics of transmissible spongiform encephalopathies (TSEs)?
TSEs are characterized by extensive death and spongiform degeneration (vacuolation) of the brain.
What is the replication process of HIV?
HIV, a retrovirus, contains reverse transcriptase, making a copy of its genome that is integrated into a host chromosome.
Fill in the blank: Viruses consist of a _______ and either DNA or RNA.
protein coat
True or False: Viroids are infectious agents that contain proteins.
False
What is the primary component of prions?
Mis-folded versions of a normal cellular protein (the prion protein PrP).
What are some transmissible spongiform encephalopathies of farm animals?
Examples include:
* Scrapie (affects sheep and goats)
* Bovine spongiform encephalopathy (BSE).
What is the significance of rapid evolution in viruses?
Viruses evolve fast, leading to the rapid and unexpected appearance of new diseases.
