CHARACTERISTICS OF VIRUSES EXAM 1 STUDY GUIDE
TOPICS:
Size
- Viruses measured in nanometers —> range from 1000 nm to 20nm diameter (yellow fever,
deadliest virus)
- Have to use an electron microscope to view
- Most abundant particles on earth
Parts
- Naked virus —> nucleic acid genome
capsid made of many capsomers (proteins)
spikes
- Enveloped virus —> nucleic acid genome
capsid made of many capsomers (proteins)
spikes
external membrane
- Host range - determined by spike + host cell receptor combination (ie. SARS CoV2 binds
to ACE2 receptor on cell membranes found in the respiratory, cardiovascular, digestive,
and renal tract)
Range can be wide or narrow depending on virus
Shape
- Helical —> capsomers arranged in a long tube (rod) where the nucleic acid genome is
placed (naked virus)
capsomers can also arranged into a tube with a coil shape (enveloped virus)
- Icosahedral —> geometric shape of 12 corners and 20 sides
size of the virus depends on how many capsomers each capsid has
can be naked or enveloped
Genome
- Can be RNA or DNA but NOT both
- Can be single or double stranded RNA or single or double stranded DNA
- Contains all necessary info of how to invade and take over host cell
- Number of genes vary from a few to a few hundred
- Can be circular or linear
- Can have single or multiple segments of nucleic acids
—> important to healthcare because the more we know about the virus genome, the more
we’re able to develop therapies that can target the proteins the virus’s genome makes
, - Retrovirus —> use enzyme reverse transcriptase to convert RNA genome to DNA and
then integrase enzyme to hide the DNA version in human host cell’s genome
Example: HIV
- RNA dependent RNA polymerase —> enzyme necessary for SARs2 to make new copies of
its genome
Replication
- Infection begins when virus is in host range and binds to comparable receptor — this is
random since viruses cannot move on their own and must bump into host cell to attach
- Adsorption = random collision of virus and comparable host cell receptor
- Penetration = naked virus brought in via endocytosis —> host cell surrounds virus in a
vesicle to bring it into its cell
enveloped virus membrane melts into the host cell membrane (fusion)
- Uncoating = naked virus exposes its genome inside host cell when vesicle and capsid break
down
enveloped virus exposes its genome when its capsid is broken down in the cell
membrane of host cell
- Synthesis = virus replicates its genome and makes more protein parts
- Assembly = protein parts are put together into new viral particles and spikes are inserted
naked —> happens in the cytoplasm
enveloped —> happens at the cell membrane
- Release = naked viral spikes eat through host cell membrane and lyse it —> immediately
kills host cell
enveloped virus released via exocytosis (blebbing/budding) —> cell dies
slowly
- Transformation = virus enters host cell and inserts their genome into host cell’s DNA
(leads to rapid division, uncontrolled growth —> cancer)
Oncovirues cause these types of cellular changes (ie. Papillomavirus and Epstein-
barr virus)
- A viruses lifecycle duration can vary depending on complexity of virus and host cell
Persistant infection = virus infects host cell and does not kill it for weeks/years
Chronic latent state = viral genome periodically reactivates and infect new cells (ie.
HIV, chicken pox)
TOPICS:
Size
- Viruses measured in nanometers —> range from 1000 nm to 20nm diameter (yellow fever,
deadliest virus)
- Have to use an electron microscope to view
- Most abundant particles on earth
Parts
- Naked virus —> nucleic acid genome
capsid made of many capsomers (proteins)
spikes
- Enveloped virus —> nucleic acid genome
capsid made of many capsomers (proteins)
spikes
external membrane
- Host range - determined by spike + host cell receptor combination (ie. SARS CoV2 binds
to ACE2 receptor on cell membranes found in the respiratory, cardiovascular, digestive,
and renal tract)
Range can be wide or narrow depending on virus
Shape
- Helical —> capsomers arranged in a long tube (rod) where the nucleic acid genome is
placed (naked virus)
capsomers can also arranged into a tube with a coil shape (enveloped virus)
- Icosahedral —> geometric shape of 12 corners and 20 sides
size of the virus depends on how many capsomers each capsid has
can be naked or enveloped
Genome
- Can be RNA or DNA but NOT both
- Can be single or double stranded RNA or single or double stranded DNA
- Contains all necessary info of how to invade and take over host cell
- Number of genes vary from a few to a few hundred
- Can be circular or linear
- Can have single or multiple segments of nucleic acids
—> important to healthcare because the more we know about the virus genome, the more
we’re able to develop therapies that can target the proteins the virus’s genome makes
, - Retrovirus —> use enzyme reverse transcriptase to convert RNA genome to DNA and
then integrase enzyme to hide the DNA version in human host cell’s genome
Example: HIV
- RNA dependent RNA polymerase —> enzyme necessary for SARs2 to make new copies of
its genome
Replication
- Infection begins when virus is in host range and binds to comparable receptor — this is
random since viruses cannot move on their own and must bump into host cell to attach
- Adsorption = random collision of virus and comparable host cell receptor
- Penetration = naked virus brought in via endocytosis —> host cell surrounds virus in a
vesicle to bring it into its cell
enveloped virus membrane melts into the host cell membrane (fusion)
- Uncoating = naked virus exposes its genome inside host cell when vesicle and capsid break
down
enveloped virus exposes its genome when its capsid is broken down in the cell
membrane of host cell
- Synthesis = virus replicates its genome and makes more protein parts
- Assembly = protein parts are put together into new viral particles and spikes are inserted
naked —> happens in the cytoplasm
enveloped —> happens at the cell membrane
- Release = naked viral spikes eat through host cell membrane and lyse it —> immediately
kills host cell
enveloped virus released via exocytosis (blebbing/budding) —> cell dies
slowly
- Transformation = virus enters host cell and inserts their genome into host cell’s DNA
(leads to rapid division, uncontrolled growth —> cancer)
Oncovirues cause these types of cellular changes (ie. Papillomavirus and Epstein-
barr virus)
- A viruses lifecycle duration can vary depending on complexity of virus and host cell
Persistant infection = virus infects host cell and does not kill it for weeks/years
Chronic latent state = viral genome periodically reactivates and infect new cells (ie.
HIV, chicken pox)
