Taxonomy of viruses Flashcards
What does -viridae ending mean
When viruses are grouped into families
What does -virus ending mean
When viruses are given a genus name
What name is given in English to viruses
Species names
On what characteristics (5) classification is based
- Nature of the host (animal,plant, bacteria,etc.
- Type of disease caused (enteric, leukemia,pneumonia)
- Life cycle(pathways of nucleic acid replication and transcription)
- Type of nucleic acids and strandedness (+strand: same as mRNA)
- Naked or enveloped
The Baltimore classification scheme is based on ____. It is useful because ____
-Based on the type of genome. Useful becasue the kind of genome will dictate the replication mechanism
What is plus RNA configuration and minus RNA configuration
- Plus configuration: same strand that mRNA( can be translated directly)
- Minus configuration: complementary to mRNA ( needs to be transcribed into plus strand before transcribed)
6 stages of life cycle of viruses
- Absorption
- Penetration
- Uncoating
- Replication
- Maturation
- Release
Describe absorption as a stage in life cycle and how plant viruses get in
Attachment of the virus to specific receptors on the surface of the cell. Plant viruses are usually introduced into the host by insect vectors, or following mechanical damage
Describe penetration as a stage in life cycle and what happens with different viruses when diffusing
Virus genome enters the cell
- In enveloped and naked viruses, the complete virion may enter the cell.
- In enveloped viruses, the envelope may be left at the cell surface such that only the nucleocapsid enters the cell
- In naked viruses, the capsid may be left at the surface
Describe uncoating as a stage in life cycle
Removal of the envelope and/or the capsid by host enzymes, sometimes within lysosomes (in eukaryotes)
Most envelope viruses of eukarytes use ___ to get in. Such viruses are then delivered to ___ where
endocytoses or viropexis, where everything gets in
They are delivered to lysosomes which degrade the capsid and the nucleic acid is release into the cytoplasm
Describe replication as a stage in life cycle
Replication of nucleic acid, transcription and protein synthesize
Describe maturation as a stage in life cycle
Assembly of virus components, nucleic acid, nucleocapsid and accessory proteins to form new virons. Usually, the assembly is spontaneous (occurs by itself)
Describe release as a stage in life cycle
Mature virions exit the host cell by means of budding or by causeing lysis of the cell. Plant viruses exit and are transmitted by means of vectors
Two periods of virus replication
- Latent period
- Rise period
What is included in latent period and rise period
Latent period: eclipse and maturation
Rise period: release
Explain eclipse
Time necessary for the host cells to replicate the viral genome and synthesize the viral components
Explain maturation
Time needed for the different components to be assembled
Explain rise period
Virions are detected outside the cell
two things can happen why the virus are detected outside:
-Lysis: virus-encoded proteins damage the cytoplasmic membrane. In bacteria, a virus-encoded protein destroys the peptidoglycan layer.
-Budding (enveloped virus)
What is burst size
Number of virions released (varies according to the virus, host cell, etc.)
What is the usual time for virus replication cycle in bacterial and animal viruses
Bacterial: 20-60 min
Animal: 8-40 h
Best-studied bacteriphages infect ___
E.coli (gram-negative)
Most phages contain ___ genomes. Most are ___, nut some have ___
dsDNA genomes
Most are naked, but some have lipid envelopes
Two types of bacteriophages
- Virulent phages
- Temperate phages
Explain what is virulent phage and give examples
Infection of host cells always leads to replication resulting in host cell lysis (lytic pathway)
Example: T4
Explain what is temperate phage and give examples
Have two options:
1) lytic pathway
2)Lysogenic pathway- the genome becomes incorporated into the bacterial host genome.
Ex.: Lambda
Lambda was discovered by
Ester Lederberg
T4 virus looks like
Usual complex virus, spider
How does T4 gets absorbed
T4 attaches to the core region of LPS by the tail fibers
What is the genome of T4
ds DNA, linear
What happens after T4 gets attached
The tail sheath contracts, forcing the central core through the outer membrane. Tail lysozymes digest the peptidoglycan layer, forming a small pore
What happens after the formation of the pore in peptidoglucan by T4
The phage DNA is then injected onto the cytoplasm of the host cell
Steps of T4 inside of bacteria
Nucelases, DNA polymerases, New sigma factors help in translation of phage DNA-> phage head proteins, tail, etc.-> mature phage particle-> T4 lysozyme prodiction->lysis
Explain lambda structure
Has no tail fibers
Has only one tail
Explain Lambda replication
As a temperate phage it can be integrated into the host genome and remain silent and under certain conditions it can exit the chromosome and continue the lytic pathway
The exit of the prophage from the choromosome is called
Excision