Virsuses Flashcards
Define virion:
Define nucleocapsin;
virion - mature virus particle
proteins attached to genome
How does +ssRNA make proteins?
How does -SSRNA make proteins?
What do RNA viruses use to make proteins/ own genome?
+ssRNA is same polarity as mRNA, translate direclty to protein, also make - strand to replicate genome into virion.
-ssRNA is complementary to mRNA, makes mRNA 1st, then protein, can also use + synthesized to make genomes for virions.
+/-ssRNA viruses use RNA dependent RNA polymerase (have to bring with them on genome/ not in host)
Why doe RNA viruses mutate rapidly?
RNA viruses have lack of proofreading mechanism to assure fidelity of other processes (i.e. DNA rep)
Retroviruses are the most error prone - due to RNA dep. DNA polymerase
What is transfection?
infection of mammalian cell by bare viral nucleic acid
Transformation
heritable change in genes/phenotype of cell from a viral infection, resulting in neoplasm (cancer).
Can be used to increase machinery for virus
Permissive cells
cells that support the complete viral life cycle, producing viral particles
Non permissive cells
don’t permit life cycle, or only permit part of it. Transformed by virus (esp DNA virus)
Defective virus
What is an example of defective virus?
virus not capable of going through entire replication unelss cell is infected w/ helper particle (complete virus)
Ex: Hepititis D virus- need B to replicate
Cytopathic effect (CPE)
observable damage to cell from infection
Describe animal viruses by:
- size
- nucleic acid
size - visible under light microscope
NA - length can vary from a few proteins to 100s
- genomes can be segemented (cause shift), or a single pieces (can be cut)
- only DNA or RNA / virus, not both
Explain the capsid
structural units (capsomers) that surround and protect viral nucleic acid
Complex - poxviruses
Icoshohedral - 2/3/5 symmetry, 20 faces/ 12 vertices
Helical
Envelope
Membrane of phospholipid bilayer taken by host cell to surround nucleocapsid
- contains virus derived glycoproteins/ proteins for attachment/fusion
Ex: Herpes Simplex
-M proteins - inner layer, help w/ viral structure
-F proteins - envelope surface, catalyze fusion w/ host cell
Which viruses are easier to inactivate: naked or enveloped?
Enveloped viruses are easier to inactivate. Lipids can be stripped away by soaps/dettergents, prevent particle from attaching to host cells. (Lose F protein)
Naked capsids are harder to kill, survive disinfection
GI viruses are naked–> hard to remove
How many classes of viruses are there? What are the classes of virus based on? (5 aspects)
DNa - 6 families RNA - 13 families based on: 1)Nucleic Acid structure 2) Symmetry of nucleocapsid 3)Envelope? 4)Capsid/virion dimension 5) NA sequence similarities
What are the steps to host cell infection?
1) Attachment
2) entry into host cell
3) viral protein/genome synthesis
4) Assembly/ release of virion
Explain attachement
Most important for specificity: viral receptors on cell surface
can also lead to tissue specificity
How does HIV enter cell?
- SU exposes Cxcr4 and Ccr5 (chemokine receptors) on CD4 cells.
- Cxcr4 = Tcell tropic strain receptor.
- Ccr5 = macrophage- tropic strain receptor. (ccr5 deletion mutation = HIV-1 immune)
- binding to receptors causes confirmational change–> fusion peptide inserts into membrane
How to enveloped viruses enter host cell?
1.F proteins catalyze fusion of viral membrane with host cell membrane
OR
2. F protein mediates phagocytosis and fusion of viral membrane and phagosome
How do naked viruses enter host cell?
- Bind to host cell at surface and capsid reearranges to allow genome out
OR - Viruses can be engulfed by receptor mediated endocytotis, causes partial breakup of capsid in vacuole–>cytoplasm for more uncoating
How does poliovirus enter cells
Naked: viroid is endocytosis, binds to receptor resulting in VP1 change, genetic material leaves into cytoplasm
How do adenovirus enter cells:
Penton base reacts w/ integrin receptor–> endocytosis, penton disassembled, capside release into cytoplasm
Capsid attaches to nuclear pore–> release of genome
How does the F protein work?
Has hydrophobic domain that grativates towards and inserts into host membrane.
This lowers activation energy of fusion
What is a syncytium?
A giant cell formed by the attachment of smaller cells to infected cell, catalyzed by F protein
What is the eclipse period of infection?
What is the latenet period of intection?
Eclipse - post entry, no formed virus particles inside or outside cell. Includes genomse synthesis.
Latent - mature particles formed inside cell, but not-outside
Do +ssRNA carry RNA pol?
No, +ssRNA don’t carry polymerase, host machinery
this makes +ssRNA infectious
How are -ssRNA/ dsRNA viral dna non infectious?
-ssRNA and dsDNA can’t immediately produce mRNA, need to by translate by cellular machinery into mRNA 1st.
What makes retrovirus (and hepadna DNA viruses) special?
Retroviruses convert RNA dsDNA, then into mRNA.
need reverse transcriptase (*RNA dependent DNA pol), and have 50-100 molecules of it in their capsule
What is “shuffling”?
If multiple viruses w/ segmented genomes infect the same cell, they can switch out segments between each other, adding genetic diversity
How are viral particles released from a cell?
- Naked virus/ some enveloped - viroids burst/ lyse cell, don’t need to use membranes
- Enveloped viruses - acquisition of the envelope of host cell as particle escapes cell (does not necesarilly kill host cell)
Hepititis B - slow release (acquisition of membrane), doesn’t kill host cell
HIV - slow release that ultimately results in cell death
Lecture 2-3
What is a localized infection?
Virus has multiplied and caused damage near the site that it entered host.
What is a disseminated infection?
- Virus enters host at specific location, multiplies locally
- Primary viremia - New virus particles spread via lymphatics to blood
- Virus multiplies in blood–> secondary viremia
- Infection of target organ.
From initial infection to blood stream, known as “incubation period”
What is an inapparent infection?
Inapparent infection = asympomatic infection resulting from attenuated virus or effective host defense
Represent unrecognized source for viral dissemination, confer host immunity.
