WEEK 1: VIRAL PROPERTIES Flashcards
Define the following terms:
1. Virion
2. Genome
3. Capsid
4. Nucleocapsid
Virion: Infectious virus particle
Genome: a set of genes
A capsid is a protein shell that encloses the genetic material of a virus.
Nucleocapsid: Genome + capsid.
What is the difference between a virus and a virion?
A virus is an obligate intracellular parasite. Accordingly, it can only survive within a host cell and depends on it for replication and metabolic processes.
Virion: The infective form of a virus when present outside of cells, which consists of DNA or RNA, a protein capsid, and sometimes an envelope.
Started in 1918
H1N1 influenza of avian origin
estimated 25 million deaths.
What virus is this?
Spanish flu
Nipah virus (NiV)
What is meant by a zoonotic virus?
Which animals are reservoirs of this virus?
State 2 main diseases caused by this virus.
- zoonotic virus(it can spread between animals and people.)
- Fruit bats, also called flying foxes, are the animal reservoir.
- Encephalitis and atypical pneumonia
Outbreaks occur almost annually in parts of Asia, primarily Bangladesh and India
Describe HIV.
HIV
retrovirus that infects cells of the human immune system (mainly CD4-positive T-cells and macrophages)
Globally, 39.0 million
630 000 deaths (2022)
Local prevalence: 20.6%
When was the first pandemic of SARS CoV?
How many cases and deaths have been recorded worldwide since December 2019
SARS –CoV
Coronavirus
First pandemic: 2002 to 2003
Guangdong province in China and extended to 29 countries.
COVID19: Wuhan China, December 2019
Over 760 million cases and 6.9 million deaths have been recorded worldwide since December 2019
State the 5 main viral properties.
*Viruses are small: sizes range 20 (parvovirus) - 300 nm (poxvirus)
*Viruses are filterable: Remain infectious after passing through a filter with pores too fine for a bacterium to pass through.
*Obligate intracellular parasites: They rely on the host.
*Genome consists of ONLY one type of nucleic acid: either RNA or DNA.
*Viral genome codes for the few proteins necessary for replication:
Proteins are non-structural e.g., polymerase,
Structural e.g., form part of the virion structure
The virus consists of a genome and an outer cover: capsid or envelope.
What is a capsid?
What is an envelope?
Capsids are either icosahedral or tubular in shape. Describe icosahedral.
Capsid: Protein shell which surrounds and protects the genome. It is made up of multiple sub-units called capsomers.
Envelope: Lipoprotein membrane, derived from the plasma membrane of the host cell.
Viral components are assembled and do not replicate by “division.”
An icosahedron is a polyhedron with 20 faces.
Describe capsid.
State 5 environments in which capsids are stable.
How is it released from the cell?
What is the capsid shape for enveloped viruses? and non-enveloped viruses.
Protein
They are stable in environments:
Temperature
Acid
Proteases
Detergents
Drying
Is released from cell by lysis.
*Helical capsid structure in enveloped viruses.
*Icosahedral capsid structure in nonenveloped viruses and enveloped viruses (all DNA viruses are icosahedral except poxvirus, which has a complex capsid)
What is an envelope?
State the 3 components of envelope.
What does labile mean in medical terms?
State the 4 environments in which envelope is labile under.
What is the function of the envelope in a virus?
What are some surface modifications found on a viral envelope?
- Membrane
*Usually originates from host cell’s plasma membrane when the virion exits the host cell (except Herpesviridae, which acquire their primary envelope from host cell nuclear membranes).
- Lipids
Proteins
Glycoproteins - Rapidly or frequently changing.
- They are labile in the following environment:
Acid
Detergents
Drying
Heat - It protects the genetic material in their life cycle when traveling between host cells. Not all viruses have envelopes.
- Spikes: viral receptor proteins (enables adhesion to host cell)
Sheath and tail fibers: present in bacteriophages
Some viruses do not possess envelopes. These are referred to as nonenveloped viruses (naked viruses).
Give examples of non-enveloped DNA and RNA viruses.
DNA viruses, e.g., Papillomaviridae, Adenoviridae, Parvoviridae, Polyomaviridae
RNA viruses, e.g., Caliciviridae, Picornaviridae, Reoviridae, Hepeviridae
Other
State 4 shapes of viruses
- Helical: spiral shape
- Icosahedral: is a geometric shape with 20 sides
- Spherical
- Polyhedral: Is a three-dimensional shape with flat polygonal faces, straight edges and sharp corners or vertices.
- Complex: complex architecture
Which of the following is the most common capsid shape of the virus?
a) Cone
b) Icosahedron
c) Cube
d) Rod
b
Arrange the following.
Family, Species, Genus, Order, Sub family
- Order
- Family
3.Subfamily - Genus
- Species
Describe the nomenclature of HHV 1according to the following:
1. Order
2. Family
3.ubfamily
4. Genus
5. Species
Order: Caudovirales
Family: Herpesviridae
Subfamily: Alphaherpesvirinae
Genus: Simplexvirus
Species: Human herpesvirus 1