Test 3-6 (Medical Viro) Flashcards
-Discuss the unique properties of viruses and their impact on the diagnosis and treatment of viral disease. -Know how the viruses that commonly infect humans are classified into families. Be able to match family names with genome makeup. -Identify each component of a virion and it’s importance in pathogenesis, diagnosis, and treatment of viral disease. -Describe the typical steps in viral replication. -Describe the effect of viral infection on host cell morphology. -List the viral genome
What is a virus?
-acellular infectious agent
-a nucleic acid surrounded by a protein coat
-obligate parasite (need to live in another organism) = -Do not carry out metabolism & -Lack organelles and ribosomes.
-20 – 300 nm in size
virus genomes
-contiguous (one long strand) or segmented (need each part)
-DNA or RNA
-single (+ sense=correct orientation for protein synthesis); - sense = not in correct order.. .ribosome cant read strand) or double stranded
matrix/tegument of virus
-in envelope surrounded viruses
-between capsid and envelope
-needed to jump start viral life cycle
viral attachment proteins are used for and found on
-on envelope or capsid in no enveope
-needed for attachment durp
ssDNA virus family
1) parvoviridae family
dsDNA virus family
1) papovaviridae family
2) adenoviridae family
3) herpesviridae family
4) poxviridae family
5) hepadnaviridae
dsRNA virus family
1) reoviridae family
-ssRNA virus family
1) orthomyxoviridae family
2) Paramyxoviridae fam
3) Rhabdoviridae family
4) Bunyaviridae family
5) Arenaviridae family
6) Filoviridae family
+ssRNA
1) Togaviridae family
2) Flaviviridae family
3) Coronaviridae family
4) Retroviridae family
5) Picornaviridae family
6) Caliciviridae family
7) Hepeviridae family
Properties of RNA viruses
-RNA is labile and transient.
-Most RNA viruses replicate in the cytoplasm.
-Cells cannot replicate RNA. RNA viruses must encode an RNA-dependent RNA polymerase.
-RNA viruses, except (+) RNA genome, must carry polymerases.
-RNA viruses are prone to mutation.
capsid types
helical
icosahedral
complex
naked capsid properties
-Are environmentally stable to the following:
Temperature;Acid;Proteases;Detergents;Drying
-Released from cell by lysis
(PROTEIN OUTERMOST SHELL)
naked capsid viruses consequences of the properties
-Spread easily e.g., on fomites, from hand to hand, by dust, by small droplets
-Dry out and retain infectivity
-Survive the adverse conditions of the gut
-Resistant to detergents and poor sewage treatment
envelope viruses properties
-Are environmentally labile, disrupted by the following: Acid;Detergents;Drying;Heat
-Modifies cell membrane during replication
-Are released by budding and cell lysis
(LIPID LAYER OUTER MOST)
envelope viruses consequences of the properties
-Must stay wet
-Cannot survive the gastrointestinal tract
-Spreads in large droplets, secretions, organ transplants, and blood transfusions
-Does not need to kill the cell to spread
VIrus life cycle summary
- attachment
- entry
- mRNA production
- protein and genome synthesis
- Viron assembly
- Egress
Attachment and entry phase
-binds plasma membrane receptor –> direct fusion of membranes
-binds receptors –> triggers engulfment of virus with cell plsama membrane (vessicle) –> virus released into cell
-(acidification of vessicle for completion prior to release
-non enveloped do same thing – instead of fusion they just lyse the vessicle
mRNA production phase
–>dsDNA - just use cells RNA pol
–>ssDNA - use cells DNA repair enzymes to make dsDNA then use cells RNA pol
–>+ssRNA (retrovirus)- rev transcriptase to make dsDNA then use cells RNA pol
–> +ssRNA (others) - dont need to do anything just make mRNA from their +ssRNA strand
–> –ssRNA - produce their own viral RNA dependent pol which uses their neg sense molecule to make mRNA
–>dsRNA - use viral RNA dep pol
biggest challenge for DNA viruses?
cellular DNA rep machinery s not avail at all times
different ways DNA viruses make cellular DNA rep machinery available
-SOLUTION 1: Make cellular DNA replication machinery available. Papovaviruses stimulate cell growth and DNA synthesis.
-SOLUTION 2: Encode viral proteins to synthesis genome. Poxviruses encode their own polymerase and enzymes to provide deoxyribonucleotides for DNA synthesis, replication machinery, and transcription machinery in the cytoplasm.
biggest challenge for RNA viruses?
no cellular RNA-dependent RNA polymerase (RdRp)
different ways RNA viruses make cellular DNA rep machinery available
-Solution 1- FOR +ssRNA viruses = encode a RdRp in genome, then since its + strand RNA the cells ribosomes will recognize your strand and make more RdRp which can make copies of genome
-Solution 2- FOR -ssRNA viruses = encode a RdRp in genome and carry the enzyme in your viron. your RdRp will work to make +ssRNA whcih is then recognized by cells ribsomes = more RdRP = more genome copies
viron assembly phase
1) Individual viral proteins form into capsid subunits
2) Subunits combine to form complete capsid.
3) Viral genome and other essential virion components are selectively packaged into capsids.
4) Envelope is acquired. (only for enveloped viruses)
5) Virus exits cell.
6) Virions mature. (only for certain viruses)
egress phase
1) budding - assembly same time as budding - a) cell plasma membrane modified to contain virus surface proteins. b) throw in whatever proteins if needed and genome c) pinch off from cell
2) lysis - cell died. Everything is assembled in house until ready to pop or cell cant hold anymore=pop
