Introduction To Viruses AMG- DLA Flashcards
Viral genomes can be:
Viral genomes can be:
Single stranded(ss), double stranded(ds), linear, circular, segmented, haploid or diploid
How do viruses appear in light microscopy?
“Invisible” by light microscopy with sizes ranging from 20-400nm
What is a virion?
A virion is a complete infectious form of virus outside the host cell (extracellular)
What do viruses infect?
Viruses infect any living organism e.g., vertebrates, invertebrates, plants, bacteria and fungi
What do viruses consist of?
Viruses are non-cellular organisms that consist of either DNA or RNA that is surrounded by a protein coat
What kind of parasites are viruses?
Obligate “intracellular parasites” that require a host cell for replication
How are virions formed?
Individual virion components self-assemble into a virion
Describe the structure of viruses
- Most viruses are structurally simple, however, some viruses have more complex structure
- The basic biophysical and biochemical rules of the viral structure and assembly are same for all viruses
What are the viral structure components?
- Genome
- Capsomere
- Nucleocapsid
- Virus specific glycoproteins
- Envelope
- tegument
What is the viral capsomere?
Viral (protein) subunits that assemble into caspid
What is the viral genome composed of?
Either DNA or RNA
What is the nucleocaspid?
Genome assembled into the caspid
Differentiate between the viral tegument and viral envelope
Viral envelope- outer layer that originates from the host membranes and covers the caspid to maintain aqueous.
Viral tegument- a cluster of proteins that line the space between the envelope and nucleocaspid
What is the structure and the main function of the virus caspid?
Structure: consists of single or several different subunits(capsomeres) that have variable size, have identifiable domains and symmetry
Held together by non-covalent, reversible hydrophobic or hydrogen bonds
What are the functions of the viral capsid?
The viral capsid serves to protect the nucleic acid and genome
What is the purpose of the viral capsid proteins?
Capsid proteins have several functions:
- define tissue or species specific transmission by interaction with host receptors to facilitate the host cell entry
- interact with the viral nucleic acid for packaging/assembling the virus.
- Assist in viral and/or host gene regulation
- Evade/block host immune system, and other functions
What are the forms of virus nucleocapsid morphology?
Three generals forms of nucleocapsid morphology:
- icosahedral(roughly spherical)
- helical
- complex (nonsymmetrical)
Describe the axes of symmetry in the Icosahedral Capsid and what causes it
The protomers assemble into pentamer
The icosahedral capsid has a complex 5-3-2 axes of symmetry e.g., poliovirus
Describe the formation of Icosahedral Capsid
- Few proteins assemble in a basic protomers
- The amount of nucleic acid that can be packaged is limited by the size of the particle.
Icosahedral capsid form independently of the genome
How do helical capsid appear?
Like rod-like, filamentous structures(May be rigid or flexible depending on the specific virus)
Where do helical capsule form?
- Capsomers bind to the viral genome in a regular fashion
- Hellical capsid are “open-ended “ and form around the genome. No empty helical capsid can form
What is common about all hellically shapes animal viruses?
All known examples of animal viruses with helical symmetry contain RNA genomes and have flexible nucleocapsid wound into a ball and surrounded by envelope, except: Rhabdoviruses
Describe the structure of the complex capsid
Bacteriophages or phages (bacterial viruses) exhibit complex symmetry
Head- nucleic acid and protein
Tail and contractive sheath
Tail fibers and tail pins
Base/end plate
Describe the capsid structure of a retrovirus
Retroviruses possess a distinctive cone-shaped capsid structure.
Retroviruses posses a 3 layer capsid that contains 11 dsRNA segments
