Exam 1 Flashcards
What are Satellites?
Composed of nucleic acid molecules that require a coinfection in order to multiply themselves.
ex. Hep D needs Hep A to coinfect cells
What are viroids?
Infectious agents of a variety of economically important plants that compromise a single small molecule of noncoding RNA.
What are prions?
misfolded proteins that can cause other proteins to also misfold and cause serious damage.
ex. CJD
How big are viruses?
Majority of viruses are in the nanometer scale
What are the 4 characteristics used to classify viruses?
Nature of the nucleic acid in the virion (DNA or RNA)
Symmetry of the protein shell (capsid)
Presence of absence of a envelope (lipid membrane)
Dimensions of the virion and capsid
What are Koch’s Postulates for viruses and infectious agents?
- The organism must be associated with the disease and its lesions
- organism must be isolated from the diseased host and grown in culture
- the disease must be reproduced when a pure culture of the organism is introduced into a healthy and susceptible host.
- Same organism must be re-isolated from an experimentally infected host
What are the issues with Koch’s Postulates?
- multiple organisms can affect pathogenesis
- finding the host and culturing the organism is a bottleneck
What are the new recent additions to Koch’s Postulates?
- Traits or markers can distinguish healthy from diseased subjects.
- inoculation of a healthy subject from a diseased subject results in transmission disease and molecular markers.
How much do viruses outnumber cellular life?
10 to 1
What are virions?
Infectious virus particles formed by de novo self assembly from newly synthesized components.
What are the common steps to all viral life cycles?
- Attachment and entry
- translation (mRNA to Proteins)
- Genome Replication
- Assembly
- release
can you remake the figure of the virus life cycle?
What is a susceptible cell?
A cell that has a functional receptor for a given virus,
note; may or may not have the components to support viral replication
What is a permissive cell?
A cell that has the ability to replicate a virus, but may or may not be susceptible (have the right receptor) for the virus to replicate.
What is a resistant cell?
A cell that has no receptor, it may or may not be able to support viral replication
What is needed for a virus to complete its life cycle?
A cell must be both susceptible and permissive
What are the three main types of cell cultures?
Primary Cell Culture
Diploid Cell Strains
Continuous cell culture
What are cytopathic effects?
Any kind of pathogensis (symptoms) that are caused by a virus
What are the broad category of cytopathic effects?
- Detachment from the surface
- cell lysis
- swelling of nuclei
- the formation of groups of fused cells called syncytium
What are syncytia?
Formations of large multinucleated cells due to viral glycoproteins binding to receptors on neighboring cells.
examples of cytopathic effects
What is virus titer?
The concentration of a virus in a sample
What is one hit kinetics?
`Only takes one particle to initiate infection
What is two hit kinetics?
It takes two different particles for replication
What is an end point dilution assay?
Measure titers of viruses that dont form plaques.
What is a transformation assay?
Determine titers of retroviruses that do not form plaques
Cells lose their contact inhibition and no longer grow as a single monolayer
What is a burst?
Viral yield form one cell after lysis.
What is the eclipse period?
The phase when infectivity is lost when virions are disassembled after entry
What is the latent period?
Time it takes to complete a replication cycle and release new virions
What was the Hershey chase experiment?
Experiment done in bacteriophages that determined that nucleic acid was the genetic code.
Radioactive proteins in viruses, next gen did not have any radioactivity.
Radioactive DNA in viruses, next gen some radioactivity was found. Use P-32
How many viral genomes are there?
7
What is the key feature of all viral genomes?
They all must make mRNA that can be read by host ribosomes
Important conventions of Plus and Minus strands
mRNA is +, it can be translated
(-) strands cant be translated directly. must be copied to make the + strand
What don’t animal cells dont have?
No known mechanisms to copy viral RNA templates to produce mRNA from them.
Baltimore Classification of Viruses. Name the 7
- dsDNA
- ssDNA
- dsRNA
- (+) ssRNA
- (-) ssRNA
- (+) ssRNA w/ DNA intermediate
- gapped dsDNA
Properties of (-) Strand RNA
No animal cell enzymes can make mRNA’s from - strands of RNA. These virus particles have RNA-Dependent RNA polymerase that they bring with them.
(+) strand RNA with DNA intermediate properties
(+) strand RNA genome of these kinds of viruses (retroviruses) is converted to dsDNA by a viral RNA-dependent DNA polymerase. (reverse transcriptase), which is then can be used as a template for host enzymes for normal RNA synthesis.
Mechanism behind dsDNA viruses
mechanism behind ssDNA
Mechanism behind dsRNA
what is RDRP replicase?
Replicates RNA genome
What is RDRP transcriptase?
synthesizes mRNA
Mechanism behind + sense ssRNA
mechanism behind - sense ssRNA
mechanism behind +sense ssRNA with dna intermediate
mechanism behind gapped dsDNA
what is subunit?
single folded polypeptide chain
what is subunit?
single folded polypeptide chain
structural unit
unit from which capsids or nucleocapsids are built
capsid
protein shell surrounding genome
nucleocapsid
core, nucleic acid protein assembly within particle. used when is a discrete substrcutre
envelope
hot cell-derived lipid bilayer
virion
infectious virus partcile
order = virales
family = viridae
genus = virus
species
Tools for viral structural observance
Electron microscope. x-ray crystallography, cryo electron microscopy, cyro electron tomography, NMR
Symmetry Rules
1 : Each subunit has identical bonding contacts with neighbor subunits.
- repeated interaction of chemically complementary surfaces at subunit interfaces leads to symettric arragnement
2: these bonding contacts are usually non-covalent. Leads to reversible and error free assembly
How many viral structures and what are they?
3
helical
icosahedral
complex
know where thefolding on icosahedral is
t x 1 = 60
to find icosahedral capsids, multiple subunit by structural units T value.
What special proteins do retroviruses bring?
Reverse Transcriptase
Integrase - integration of proviral DNA into cellular genome
protease: production of infectious particles.
What special proteins do retroviruses bring?
Reverse Transcriptase
Integrase - integration of proviral DNA into cellular genome
protease: production of infectious particles.
2 important components for infections be COVID 19
ACE 2 receptor and TMPRSS2 protease cell surface for priming and entry.
Covid 19 is +ssRNA virus
2 important components for infections be COVID 19
ACE 2 receptor and TMPRSS2 protease cell surface for priming and entry.
Covid 19 is +ssRNA virus
what is epitope?
binding site of protein
Viruses are obligate intracellular parasites
