chapter 5 Flashcards
What are the two commonly used methods of classifying viruses?
Morphology and nucleic acid type
Additional classification methods include mode of replication, host organism, and disease they cause.
Define capsid.
The protein coat of a virus that encases its genetic material
The capsid is composed of proteins coded by viral genes.
What are capsomeres?
Subunits that make up the capsid
Capsomeres are formed from protomers.
What is a nucleocapsid?
The combination of the viral capsid and the viral nucleic acid
Nucleoproteins are associated with nucleic acids.
Define virion.
A fully assembled virus that is capable of infecting a host cell
Virions are the complete, infectious form of a virus outside a host cell.
What is a viral envelope?
A lipid membrane that surrounds the nucleocapsid in some viruses
It is typically obtained from the host cell membrane.
What are the types of viral genomes?
DNA or RNA, which can be dsDNA, ssDNA, dsRNA, or ssRNA
The nucleic acid can be linear or circular.
What is the Baltimore Classification System?
A system that classifies viruses based on the relationship between viral genome and messenger RNA
It includes seven groups.
How do bacteriophages multiply?
Through adsorption, penetration, replication, assembly, maturation, and release
Bacteriophages specifically infect bacteria.
What is the first step in the multiplication of bacteriophages?
Adsorption
This involves the phage attaching to a susceptible bacterial host.
What occurs during the penetration phase of bacteriophage multiplication?
The phage injects its nucleic acid into the bacterium
Only the nucleic acid typically enters the bacterial cell.
What is the eclipse period in bacteriophage multiplication?
The phase where no infectious phage particles are found in the host cell
It occurs after the virus has entered the host but before it has replicated.
What are lytic phages?
Bacteriophages that destroy the host cell by lysis after multiplication
Newly formed phages are released into the environment.
What is a prophage?
Phage DNA integrated into the host chromosome
This occurs during the lysogenic cycle.
List the stages of animal virus multiplication.
- Adsorption
- Penetration
- Uncoating
- Replication
- Assembly
- Release
The duration of the cycle varies between different viruses.
What is the role of uncoating in viral multiplication?
Releases the viral nucleic acid into the host cell
This process varies depending on how the virus enters the cell.
What are the two methods of release for mature virus particles?
- Budding (exocytosis)
- Lysis
These methods determine how the virus exits the host cell.
What is an abortive viral infection?
An infection without viral production
The host cell does not produce new virus particles.
What characterizes persistent viral infections?
- Chronic: Not lytic but productive
- Latent: Limited synthesis with no viral production
Examples include cold sores and shingles.
What are the morphological effects of viral infections on host cells?
- Altered shape
- Detachment from tissue surface
- Lysis
- Membrane fusion
- Inclusion bodies
- Cell death
These changes can lead to cytopathic effects.
List some DNA viruses that infect humans.
- Adenoviruses
- Hepadnaviruses
- Herpesviruses
- Papillomaviruses
- Poxviruses
Each type has associated diseases.
List some RNA viruses that infect humans.
- Bunyaviridae
- Coronaviruses
- Orthomyxoviruses
- Retroviruses
- Flaviviruses
These viruses are linked to various diseases.
Compare and contrast viroids and virusoids.
Viroids do not need a helper virus; virusoids require one
Viroids generally cause plant diseases, while virusoids are associated with plant infections.
What are prions?
Infectious proteins that can cause transmissible spongiform encephalopathies
They are abnormally folded proteins lacking nucleic acid.
