1. Intro to Virology Flashcards
what do viruses infect?
all living things
how many virus particles do we encounter per day? how do virus particles outnumber cellular life?
billions!
outnumber cellular life 10:1
what has the greatest biodiversity on earth?
viruses
do we carry viral DNA?
how much of blood plasma DNA is viral?
yes, we carry viral DNA as part of our own genetic material
about 70% of DNA from blood plasma is viral
3 reasons why viruses are beneficial
- drive global cycles (i.e. catalyze movement of nutrients from organisms, kill 20-40% of ocean microbes, regulate earth’s ecology)
- transfer genes btwn organisms
- prevent and cure disease
what 7 things have viruses told us about cell biology?
- promoters for euk RNA pol
- DNA replication enzymes
- reverse transcriptase
- RdRP
- RNA splicing
- Translation
- Identification of oncogenes
what is a virus?
INFECTIOUS, OBLIGATE, intracellular parasite
what 2 things do viruses contain? what is one additional thing that viruses may contain?
- genetic material
- protein capsid coat
may have envelope from host cell membrane
why did we previously not realize that viruses could be large?
we used to identify viruses by filtering, so we did not see the larger viruses
what are the 2 phases of viruses?
- inanimate phase –> virion
- multiplying phase –> in infected cell
are viruses active or passive?
passive –> they don’t actually do anything
how were viruses first visualized?
electron microscopy
what are 4 ways that viruses are classified based on physical attributes?
- nature and sequence of nucleic acid virion
- symmetry of capsid
- presence/absence of envelope
- dimensions of virion and capsid
what are the 7 taxonomy classes?
- kingdom
- phylum
- class
- order
- family
- genus
- species
what is the suffix for the ORDER name of viruses?
-VIRALES
what is the suffix for the FAMILY name of viruses?
-VIRIDAE
what is the suffix for the GENUS name of viruses?
-VIRUS
what are the 7 steps of a virus infectious cycle?
- receptor binding
- entry and uncoating
- early gene expression
- replication of viral genome
- late gene expression
- assembly of virions
- exit
describe RECEPTOR BINDING
- virus-encoded proteins recognize and bind to cells at a receptor
what can a viral receptor be made of?
protein, carbohydrate, lipid
describe tropism
tropism = the type of cell a virus affects
determined by the receptor and replication machinery
what are cellular receptors specific for?
specific for each virus and host species
how do bacteriophages enter the cell?
they have tails that drill holes and then inject their genome into the host cell
how do plant viruses enter the cell?
damage the cell wall then penetrate thru
how do animal viruses enter the cell?
membrane fusion OR endocytosis
what happens to a virus once it is inside the cell?
uncoating –> capsid disintegrates to release the genome
describe EARLY GENE EXPRESSION
viral genome directs expression of early protein –> depends on type of genome
describe REPLICATION OF VIRAL GENOME
early proteins promote replication of the viral genome –> allowing cell to become factory for expression and replication of viral genome
describe LATE GENE EXPRESSION
late mRNA are made from newly replicated genomes to produce STRUCTURAL proteins (ex. glycoproteins from capsid proteins)
are early or late proteins expressed in greater quantities?
LATE
describe the ASSEMBLY OF VIRIONS
structural proteins package viral genomes and assemble the capsid
what do enveloped viruses encode for the assembly of virions?
enveloped viruses encode glycoproteins that insert into lipid membranes to direct formation of viral envelope
describe EXIT
virions released via:
A. death and lysis of host cell
B. budding from cell membrane to form envelope
what do all viruses must make?
ALL viruses MUST make mRNA to be translated by host ribosomes
why are viruses considered parasites?
parasites of the host protein synthesis machinery
what is the strategy of viral propagation?
pre-form the components and then assemble into the final product
describe viral propagation if all cells are infected
ECLIPSE PERIOD - no infectious particles, but virus is replicating, etc.
BURST/YIELD - release of virions
describe viral propagation if a few cells are infected
there are more cells than virions so after the initial burst, neighbouring cells are infected and a second burst occurs
