Taxonomy of viruses Flashcards
Virus are given 3 different names…
- Into FAMILIES: end in viridae
- Viruses are given a genus name : end in virus
- Viruses are given a species name: Usually in english, descriptive
Classification of viruses is based on different characteristics. Name them…
- Nature of the host (ex: bacteriophage infect bacteria)
- Type of disease caused (ex: murine leukemia virus)
- Life cycle (pathways of nucleic acid replication and transcription)
- Naked or enveloped
- Type of nucleic acids and strandedness (+ strand = same as mRNA)
What is the baltimore classification scheme?
-Scheme where classification is based on the type of genome. It is useful because THE KIND OF GENOME WILL DICTATE THE REPLICATION MECHANISM.
What are RNA genomes?
+ configuration: Same strand than mRNA (can be translated directly)
- configuration: complementary to mRNA (needs to be transcribed into + strand before it can be translated)
What are the 5 steps of the life cycle of viruses?
- Attachment ( absorption)
- Penetration
- Synthesis of nucleic acid and prots
- Assembly and packaging
- Release (lysis)
OR
- Absorption
- Penetration
- Uncoating
- Replication
- Maturation
- Release
What happens during the penetration step of a viruses life cycle?
The virus genome enters the cell:
- In ENVELOPED AND NAKED VIRUSES: the complete virion ma enter the cell
- In ENVELOPED viruses , the envelope may be left at the surface of the cell, such that only the nucleocapsid enters the cell
- In NAKED viruses, the nucleocapsid may be left at the surface
What is uncoating in the life cycle of the virus?
removal of the envelope and/or the nucleocapsid by host enzymes, sometimes within lysosomes (in eukaryotes)
What are the 3 penetration method used by viruses?
- Direct penetration
- Membrane fusion
- Endocytosis
What penetration method is most commonly used by ENVELOPED VIRUSES OF EUKARYOTES?
Most enveloped viruses of eukaryotes use endocytosis (VIROPEXIS). Such viruses are then delivered to lysosomes which degrade the nucleocapsid and the nucleic acid is released into the cytoplasm.
What happens during the maturation phase of lice cycle of viruses?
- assembly of virus components, nucleic acid, nuceloapsid and accessory prots to form new virions
- Usually, the assembly is spontaneous
What happens during the release phase of life cycle of viruses?
- Mature virions exit the host cell by means of BUDDING or by causing lysis of the cell. Plant viruses exit and are transmitted by means of vectors.
What are the main phases ( on the curve) of virus replication ? What subphase does it include?
Latent Phase: eclipse + maturation
- ECLIPSE : time necessary for the host cells to replicate the viral genome and to synthesize the viral components - MATURATION : time needed for the different components to be assembled.
Release phase (RISE period)
- Virions are detected OUTSIDE the cell - LYSIS : damage of cytoplasm (in bacteria, destroy peptidoglycan layer) - BUDDING: developed virus
What is the definition of Burst size?
Number of virions released
What type of DNA do most of the phages contain?
Most of the phages contain LINEAR dsDNA genomes. Most are NAKED, but some possess lipid envelope.
What are the 2 pathways of a viral life cycle?
LYTIC PATHWAY: in virulent phages, replication results in host cell lysis–> T4
LYSOGENIC PATHWAY: in temperate phages, the genome becomes incorporated into the bacterial host genome –> Lambda
What type of phage is T4 bacteriophage?
Virulent phage
How does bacteriophage T4 invade a host?
- Absorption: T4 attaches to core region of LPS by the tail fibers
- Tail sheath contracts, force central core through outer membrane. LYSOSYMES of the tail digest peptidoglycan layer, forming a pore
- The phage DNA is then injected into the cytoplasm of the host cell.
How do we call a prolonged, latent state of infection?
lysogeny
What kind of phage is Lambda?
temperate phage
What is a prophage?
Phage genome within the host cell chromosome
What is Lysogen?
bacterium that contains a prophage
What are the 2 pathways possible in the infection of Lambda bacteriophage?
Lytic pathway and lysogenic pathway (see slides…)