MIDTERM LEC 3: BASIC CONCEPTS OF VIROLOGY Flashcards
The word “virus” came from which Latin word?
vīrus
Vīrus means
poisonous fluid
or venom
Submicroscopic, obligate intracellular
parasite, and among the smallest of all infectious agents
virus
What does “obligate intracellular parasite” mean?
they cannot grow outside of living cells
T/F: Viruses are the most frequent cause of human infectious disease
T
T/F: There is NO viral infection among any animals, plant, or bacterial cell
F
Brick shaped virus with hollow spikes
poxviruses
Largest and most complex virus
poxviruses
Size of poxviruses
250x350nm
Smallest human virus
poliovirus
Size of poliovirus
25nm
Poliovirus belong to what family
picornaviridae
Smallest DNA virus
parvovirus
Largest RNA virus
paramyxovirus
T/F: Viruses can contain RNA or DNA at the same time
F (either of the 2 only, never both)
How many families of virus are associated with human infections?
21
How many families of RNA viruses are associated with human infections?
14
How many families of DNA viruses are associated with human infections?
7
T/F: Viruses can multiply by binary fission
F (they cannot)
Refers to the specificity of viruses and how they can only infect a limited number of hosts.
viral tropism
Enumerate the viral mode of transmission
● Fecal-oral route
● Sexual contact
● Trauma or injection of contaminated objects ●Tissue transplants (BT)
● Arthropod or animal bites
● Transplacental
Local infection leads to ________ then to other tissues (systemic)
viremia
Viruses that have the ability to stimulate uncontrolled growth of host cells
oncogenic viruses (cancerous)
The classification system of virus is determined by what committee
International Committee on
Taxonomy of Viruses (ICTV)
The ICTV classification system is based on what 2 properties
chemical and physical properties
(like genome type, # of proteins encoded, nucleic acid sequence, virion shape, capsid shape, envelope, etc.)
In general, how many taxonomic ranks are widely used?
5
What are the widely used 5 taxonomic ranks?
- order
- family
- subfamily
- genus
- species
Suffix used for the taxonomic rank “order”
-virales
Suffix used for the taxonomic rank “families”
-viridae
Suffix used for the taxonomic rank “subfamilies”
-virinae
Suffix used for the taxonomic rank “genus”
-virus
T/F: Classification of viral species can be
problematic and therefore is often polythetic
T
Polythetic meaning
members of the group may share common characteristics but may not have a single defining characteristic
3 basic properties in viral classification
- viral morphology
- method of replication
- presence or absence of lipid envelope
Classification system that is based on the type of nucleic acid genome and replication strategy of the virus
baltimore classification system
Baltimore classification system was devised by a Nobel laureate named
David Baltimore
In what year was the baltimore classification system devised?
1970
Baltimore classification system was based on
- the type of nucleic acid genome
- replication strategy of the virus
Viruses are classified into how many classes
7 classes
Class I
dsDNA viruses
Class II
ssDNA viruses
Class III
dsRNA viruses
Class IV
positive sense ssRNA viruses
Class V
negative-sense ssRNA viruses
Class VI
RNA viruses that reverse transcribe
Class VII
DNA viruses that reverse transcribe
Complete infectious viral particles
virions
Viral structure that constitutes the genetic material or viral genome which can be single or double stranded DNA or
RNA
nucleic acid core
Viral structure that introduces viral genome into host cell
capsomere
It protects viral genome/nucleic acid core against destructive agent external environment
capsomere
Complex morphologic units of the capsomere which consist of several identical or different protein molecules
capsid
Protein shell, or coat, that encloses the nucleic acid genome
capsid
This is a repeating structural unit
capsomere
Types of capsids in symmetry
- helical capsid
- icosahedral capsid
Type of capsid that is cubical and has 20
flat sides
icosahedral capsid
Type of capsid that is irregular
helical capsid
Nucleic acid genome surrounded by a symmetric protein
nucleocapsid
Lipoprotein envelope that covers the capsid and is acquired from the host cell
peplos/viral envelope
host cell membrane/plasma membrane/nucleic acid membrane
peplos/viral envelope
What do you call a virus with envelop
enveloped virus
What do you call a virus with no envelope
naked virus
What type of virus is susceptible to inactivation such as high temperature, high pH
enveloped virus
Enveloped virus may contain what protein, which lies between the envelope and nucleocapsid?
matrix protein
Glycoprotein molecules that bind to host cell
during attachment
glycoprotein spikes
Glycoprotein spikes are readily visible under what type of microscope?
electron microscope
Viruses with glycoprotein spikes
- SARS-CoV-2
- HIV (Human Immunodeficiency Virus)
- EBV (Epstein-Barr Virus)
Target receptor of HIV
CD4
Target of SARS-CoV-2
ACE
Target receptor of EBV
C3D
Occurs when a virus infects a host cell by which proliferation of viral genomes transpire to cause further infection to the host’s body, resulting in a disease or infection
viral replication
Enumerate in order the infectious cycle of virus
- Attachment
- Penetration
- Uncoating
- Macromolecular Synthesis
- Assembly
- Release
(APUMAR)
AKA adsorption
attachment
It is where the recognition of a suitable, specific host cell occurs (viral tropism)
attachment
What must adsorb or attach to the cell surface since viruses are unable to diffuse across biological membranes?
virions
Why do viruses can’t diffuse across biological membranes?
because virus particles are too large to diffuse across the plasma membrane
The virus attaches to specific receptors on
the surface of a susceptible cell by means of specialized structures on its surface, called?
adhesion molecules
AKA viral entry
penetration
Provides an opportunity to internalize the virus
penetration
Virus enters the host cell by several mechanisms that are virus-dependent. Enumerate the mechanisms
- Direct penetration
- Fusion method
- Receptor-mediated endocytosis
A penetration mechanism in which the viral envelope fuses
with the host’s plasma membrane
fusion method
A penetration mechanism which is possible for naked viruses
direct penetration
A single cell with several nuclei
syncytia
In this mechanism, there is a binding of infected host cells with nearby host cells, forming syncytia
fusion method
A penetration mechanism that involves phagocytosis by the host cell; most
common mechanism of viral penetration.
receptor-mediated endocytosis
The breakdown/removal of the capsid, causing
the release of the virus genome into the cell
uncoating
T/F: Uncoating do not occur simultaneously along with or just after penetration
F (they occur simultaneously or just after penetration)
Once the virus loses its protein coat, it releases its
viral genome
RNA viruses are released in the
cytoplasm
DNA viruses are released in the
nucleus
T/F: The virus forces the host cell to make millions
of copies that leave the cell and spread
T
