Virus Structure Flashcards
Size
Viruses are small ~ 100nm
Types of host:
Arthropods
Dengue
Types of Hosts:
Bacteria
T4 phage
Types of Hosts:
Animals
Foot and Mouth Virus
Types of hosts:
Plants
Tobacco Mosaic Virus
Shape
Icosahedral
Helical
Nucleic Acids
Double stranded:
DNA or RNA
Single Stranded:
DNA or RNA
Virus Basics:
Classification
- Originally viruses were classified only by size
- Filterability
- Viruses were then classified by pathogenic properties, transmission, ecology, or organ tropisms
- yellow fever, hepatitis A, B, and C; Rift Valley Fever virus would all be hepatitis viruses
Virus Basics:
Classification
lineage
- Order:
- -virales
- Family
- -viridae
- most common grouping
- Sub-family
- -virinae
- Genus
- -virus
- Species or common name
- Isolate, strain, variants, genotype, group, clade
- “Species” not commonly used but can be best defined as viruses that “share common features”
Virus Basics:
Classification:
Types of Viral Genomes
- composition
- DNA or RNA
- Form
- Single stranded, or double stranded
- Polarity for single stranded RNA genomes
- positive
- negative
- ambisense
Virus Basics:
Viral Genome
Must make mRNA that can be read by the host ribosomes
mRNA is + sense RNA
mRNA can be translated into a protein
Virus Basics:
Reverse Transcriptase
Unique to Retroviruses
Cells do not have a polymerase to turn RNA into DNA - the virus must bring its own reverse transcriptase
Virus Basics:
Viral Genome:
Coding regions
genes that produce proteins
- Open reading frame (ORF):
- has a start codon, stop codon, and intervening sequence that codes for a polypeptide of at least 100 amino acids
- non-structural proteins
- participate in processes important to the virus.
- Structural Proteins
- components of the virion. Envelope proteins, matrix proteins, capsid proteins, additional virion associated proteins, provide receptor binding sites
- non-structural proteins
- has a start codon, stop codon, and intervening sequence that codes for a polypeptide of at least 100 amino acids
Virus Basics:
Viral Genome:
Non-Coding regions
Untranslated regions
- Contains:
- regulatory elements
- Scaffolding
- Terminal repeats
Virus Basics:
Viral Genome
Contain information for
Replication
Assembly and packaging
Regulation of the replication cycle
Modulation of host defense
Spread
Virus Basics:
Viral Genomes
DO NOT contain information for
complete protein synthesis
Membrane synthesis
Energy production
Virus Basics:
Capsid
Protein shell surrounding the nucleic acid genome
- Slef-assemble into a “minimum structure, maximal space” to stably package the genome
- Two main types
- symmetrical
- icosahedral and helical
- Complex
- symmetrical
Virus Basics:
Symmetrical Capsid
Icosahedral
Parvovirus
20 equilateral triangles
Made up of 60 identical copies of the capsid protein
Minimal Structure, maximal space to stably package the genome
Virus BadicsL
Summetrical Capsid
Helical Symmetry
- Cylindrical structure
- Capsomeres are arranged in a spiral straircase with a central pole as the axis
- Rhabdovirus (rabies)
- Coiled helical nucleocapsid with a bullet shaped virion morphology
Virus Basics:
Capsid:
Complex Capsid
Not helical or icosahedral
Possess no symmetry
Filoviridae and poxviridae
Virus Basics:
Capsid:
Function
Genome packaging
Host cell attachment and entry
Un-packaging of hte genome and release into cells
Viral Basics:
Nucleocapsid
The complete protein - nucleic acid complex that is the packaged form of the genome in a virus particle
Virus Basics:
Envelop
Enveloped Viruses
- Lipid Envelop
- Capsid
- Genome
- Derived or “stolen” from the host cell membrane because the viral genome does not have the machinery to encode a lipid bilayer
Virus Basics:
Envelope:
Function
- Membrane Glycoproteins
- antigenic sites, attachment, fusion
- Protects the nucleocapsid
- capsid with the viral nucleotides
- Facilitates direct transmission of virions to adjacent cells
- Camouflage
- surrounded by host material
- More unstable in the environment
Virus Basics:
Envelope:
Structure
The E protein is the major structural protein on the surface of mature flaviviurs virion
Each monomer of E protein consists of three domains
Virus Basics:
Envelope:
Fusion with host cell
What is a Virus?
- Obligate intracellular parasite
- Infectious to a variety of living organisms
- Humans, Animals, Plants, Bacteria, Invertebrates, Fungus
- Viral genome is packaged in a cell and has all the information that a virus will need to replicate and be transmitted form one host to another
- Viruses are not alive
- maybe viruses are a transitional life form between things that are not living to things that are living
- Also a transition form RNA genome to DNA genome
- Virus partile is not alive on its own it needs to infect a cell
- Viruses do NOT
- reproduce
- Evolve
- Metabolize
- … without first infecting a cell
