micro - virus stuff Flashcards
What is an obligate intracellular parasite?
VIRUS!!!!
What is the point of vaccines?
generate enough anti-viral compounds to prevent multiplication within the body
What is a virion?
the infectious virus particle in viruses - contain nucleic acid genetic material surround by a protein coat (CAPSID); some viruses also have a lipd and glycoprotein ENVELOPE
What do you need to know about genomes?
- can be either DNA or RNA and ss or ds - ss RNA genomes can have the same (+) or complimentary (-) polarity as viral m-RNA (ie - if (+) polarity, can go straight to being made!!!!! if (-) polarity, the complimentary strand must first be made - may be linear or circular; some linear RNA genomes are segmented - viral genomes are usually haploid - just the retroviruses are diploid
What are capsids?
- The capsid and genome of enveloped viruses is called a nuceocapsid
- Capsids or nucleocapsids are composed of many copies of one or very few viral-encoated protein subunits
- Capsids function in packaging of the nucleic acid in viral assembly and protection of the nucleic acid
- Capsids of naked viruses contain the viral attachment protein (VAP)
What are the 2 shapes of capsids?
cylindrical (helical form)
cubic (icosahedron form)
How are capsomers arranged?
in penton capsomers (surrounded by 5)
in hexon capsomers (surrounded by 6)
What is the envelope?
- Composed of lipids, proteins and glycoproteins
- Specific glycoproteins act as VAPs for enveloped viruses
- Acquired from viral-modified cellular membranes during egress of virus from host cell
- Is disrupted in non-moist environments or by heat, acid and lipid solvents
How many virus families have human pathogens and now many contain DNA?
Human pathogens are found in 21 families; 7 families contain DNA
What is VAP?
viral attachment proteins found on the virion; allow virus to get into next cell
on envelope virus found in membrane
in naked virus (no membrane), part of capsid protein
(always what’s external)
Very important!
How are viruses classified?
basis of
nucleic acid
virion structure
replication strategy
Viruses in the same family can:
produce diverse diseases (chicken pox, herpes, mono)
Viruses in the same families can…
produce the SAME disease
Which is the only diplo virus?
retrovrirus - AIDS (2 strands of +sense DNA)
There are __________ for viruses to replicate.
there are DIFFERENT WAYS for viruses to replicate - more complex ways for RNA.
whole point = they must replicate to cause disease. We want to stop them.
What does host range depnd on?
1) can a virus enter a cell
2) can virus find appropriate cellular machinery
3) can virus exit cell
What is a productive virus?
one that yields new infectious viruses
What is a non-productive virus?
viral genetic material persists in a cell (latent state) but no infectious viruses is formed
Some non-productive infections can lead to oncogenic transformation of cells.
What are the phases of viral muliplication?
1- attachment
2- penetration
3- uncoating
4- virus component synthesis
5- assembly
6- release
- if not attached, won’t cause diease. Disease shows up where it’s possible to attach -
The synthesis of viral proteins and viral effects on host macromolecular synthesis often result in morphological changes to the host cell collectively known as cytopathic effects (CPE), ex., cell rounding, cell fusion, etc.
Antivirals inhibit some step in the viral multiplication process
Where do RNA viruses generally replicate and what are the exceptions?
in the cytoplasm - except for the Aids virus (retro-virus; must go to nucleus) and the influenza virus (needs enzymes found only in nucleus of cell).
Where do DNA viruses normally replicate?
in the nuclues
What are viroproteins?
small, hydrophobic virus-encoded proteins that oligomerize at host cell membranes where they are involved in enveloped virus budding and non-enveloped virus cellular lysis.
even without lysing the cell, they’ve just made the cell incapalbe of doing its job
have several cytopathogenic effects on the cell including
- formation of hydophilic pores
- alterations of calcium and hydrogen gradients.
Viral specific membranes host cytoplasmic membrane. Nucleocapsid migrates, buds, is released
Since virus messes with the cell membrane, now is recognized as foreign and killed by immune recepters. Dead cells cause disease…
What are the eclipse and latent periods in the 1-step growth cycle?
elclips = when its inside the cells…nothing is visible…
latent = right until the infectious disease is released
of infected cells you get from 1 virus depends on particular virus and particular cell (stage cell is in, etc. )
Which RNA viruses do not replicate in the cytoplasm of the cell?
orthomyxoviruses - flu & retro viruses
Are (-) sense RNA viruses enveloped or naked?
enveloped
Do RNA viruses make their own replicase/transcriptase?
Yes, because cells don’t have cytoplasmic RNA polyerase, so must make their own.
What kind of polarity do ss RNA viruses have?
(+) sense (messenger polarity)
(-) sense (antimessenger polarity)
and ambisence polarity (both + and -)
RNA virus genome Replication:
- (-) sense RNA viruses have replicase/transcriptase associated w/RNA within the virion
- all ss RNA viruses (excpet retro) replicate using a ds RNA intermediate
- retro have a nuclear phase, invovling a reverse transcriptase in their genomic RNA replication
The spontaneous mutation frequency of RNA viruses is higher than the DNA viruses because their RNA pol are not as accurate in duplication.
Expression of RNA genome
- transcrip. of orthomyxovirues and retrovirus mRNA occurs in the nucleus
- RNA viruses have deveoped unique mech. to produce indiviual polypeptides from polycistronic RNA (since that is not a propery of euk. cells)
- picornavirus synthesize polypeptides that are then cleaved by viral proteases
- individual initiation an dtermination signals appear throughout RNA of rabies virus
- all TX begins on 3’ end, but pol. slides over various size intervening sequences to yield transcript of various compositions and lengths
- orthomyxoviruses ad retroviruses have segmented genomes (each segment codes for 1-2 polypeptides that are necessary for replication) **REMEMBER**
- retroviruses have spliced transcripts
- Some RNA viruses use a combination of strategies
if a virus is (-) sense…
usually comes w/enzyme to make the + sense: all (-) sense have replicase: THE ENZYME THAT ALLOWS TX OF VIRUS TO OCCUR IS ATTACHED TO EACH OF THE SEGMENTS
and there are at least 2 THAT REQUIRE THE NUCLEUS OF THE CELL IN ORDER TO REPLICATE
ALSO THERE ARE SOME STEPS IN REPLICATION THAT ARE UNIQUE TO EACH VIRUS (think protease in HIV)
What is the differnece between early and late proteins in RNA synthesis?
- early proteins made = the ones invovled in replication of nucleic acids
- late proteins made = viral structural proteins; either envelope or capsid
where does replication of viral DNA occur?
in nucleus, except for POXVIRUSES - which replicate entirely in the cyt
Which phase is necessary for viral DNA replication?
the host functions expressed during S phase are needed
If not in S-phase, it is a NONPRODUCTIVE INFECTION
Which DNA viruses cannot transform cells?
Parvoviruses - all other DNA viruses can transform cells
What are the non-productive infections caused by some DNA viruses called?
latent
can’t cure in latent stages
what helps determine tissue trophism and host range of viruse in DNA viruses?
avail. of host cell DNA binding proteins for TX
What kind of nuclear DNA viruses have ds DNA?
Which of the 3 types can transform cells?
adenoviruses
herpesvirues
papovaviruses
(some strains of all 3 types can trasform cells)
What kind of nuclear DNA viruses have a PARTIALLY DOUBLE-STRANDED DNA genome?
hepadnaviruses
- these replicate their DNA in the nucleus via a RNA intermediate,
- involve a RNA-dependent DNA pol (reverse transcriptase) in their replication
- can transform cells
so, some strains of HepB can be treated using reverse-transcriptase inhibitors developed for AIDS virus.
envelope virus enters cell: paritally ds DNA goes into cell, after its uncoded into nucleus…from ds DNA is made pre-genome RNA -> used to make full-length copy of DNA -> reverse TX used to make DNA -> escapes from cell when partially complete. (Has to have pre-genomic DNA, so must go to nucleus)
Parvoviruses:
- have ss DNA genome
- enter nucleus thru nuclear pores
- ss DNA forms hairpin structures which self-primes cellular DNA pol to synthesize complimentary strand
- ds DNA uses cellular DNA pol and viral specific endonucleases to form genome DNA
SOME VIRUSES NEED A HELPER VIRUS TO REPLICATE THEMSELVES
Cytoplasmic DNA Viruses
ie POXVIRUSES
- have ds DNA genome
- provide their own mRNA and DNA synthetic machinery
- code for viral DNA dependent RNA plymerase and mRNA modifying enzymes for processes like capping and methylation
- Poxviruses synthesize their own envelope
Hepadnaviruses replicate in ____ using _______
nucleus; reverse TXase
Pox viruses replicate ______ using ________
cytoplasm, using DNA dependent RNA pol - this allows them to replicate in cyt. w/out going to nucleus
Do DNA tumor viruses transform permissive or nonpermissive cells?
DNA tumor viruses lyse permissive cells; they only transform non-permissive cells
Do RNA tumor cells transform permissive or nonpermissive cells?
PERMISSIVE
what is a permissive cell?
replicates totally in a cell
What is a nonpermissive cell?
just infects cell, can’t replicate
Do oncogenes go with DNA or RNA?
Some RNA tumor viruses carry oncogenes responsible for the transformation
Are tumor viruses DNA or RNA related?
All tumor viruses are DNA viruses or generate a DNA provirus (Retrovirus)
although,
Certain DNA and RNA viruses are associated or implicated in human cancers
what is cellular transformation?
Cellular transformation is a stable, heritable change resulting in poor or no control of cellular growth
Carcinogenesis is a multistep process involving multiple genetic changes
Cellular transformation results in the alteration of cellular processes and properties which can result in altered morphology, growth control and cellular and biochemical properties
Human papillomaviruses are in what family and what human cancers do they cause?
Papovaviridae
- genital tumors
- squamous cell carcinoma
What family are the EBV virus and Herpes simplex type 2 in, and what cancers do they cause?
What family is the Hep B virus in and what cancers does it cause?
hepadnaviridae; hepatocellular carcinoma
what family is the HTL virus in and what cancer does it cause?
retroviridae; adult T cell luekemia
What is the “master break” in the cell cycle?
the p-1-10-RV protein. So long as pRB is active, do NOT have unctrolled growth…so long as phosphorylated, its active.
what does inactive p53 do to pRB?
when active, it turns on p21, which turns on kinases, which phosphorylate master break protein, which turn it on
so, inactive p53 turns off pRB
What are c-onc?
mutated forms of normal cellular genes (proto-oncogenes
they code for a heterogeneous group of proteins that are invovled in normal cell division or differentiation pathways
abnormal expression/regulation lead to cellular transformation or cancerous growth
what are V-Oncs?
viral oncogenes: copies of cellular oncogenes that have been aquired by certain viruses during replication
present in the viral genome
responsible for the cellular transforming activity of those viruses which contain them
what are tumor suppressor genes?
negative regulators of celluar groth
sometimes called anti-oncogenes or growth supressor genes
cause cellular transformation if the functional activity of both allelles is lost
EXEMPLEFIED BY Rb GENE AND THE p53 GENE!!!!!!!!!!!!!!!
what do nonreceptor protein tyrosine kinases do?
when expressed in non-regulated form, will get unregulated growth downstream
what do receptor protein tyrosine kinases do?
when receptor is activated, will phosphorylate something (not linked to receptor)
what do oncogenes do?
cause unregulated growth
what is RB
codes for pRB protein, master brake of cell cylce. Invovled in retinoblastoma and bone, bladder, small cell lung and breast cancer
as long as active, have control
if not phosphorylated, it’s inactive, control is lost
what is p53?
codes for the p53 protein, which can halt cell division and induce abnormal cells to kill themselves. Invovled in a wide range of cancers.
Tumor virus - host cell interactions
SUMMARY
DNA tumor viruses transform non-permissive cells; they kill permissive cells
DNA tumor virus rarely produce tumors in the natural host (human DNA tumor viruses are the exception)
RNA tumor viruses transform both permissive and nonpermissive cells and do produce tumors in the natural host
Which cells do DNA tumor viruses transform?
NONPERMISSIVE; kill permissive cells
EBV, HBV, HSV, and HPV are associated with human cancers
What are the transformation characteristics of Adenoviruses?
Transform rodent cells (need more stuff to finish than rodent cells have…)
No association with human neoplasms
Types of Adenoviruses and oncogenic potential:
Vary in their oncogenic potential from high to not at all
Types 12, 18 and 31 are highly oncogenic
transforming proteins associated with Adenoviruses:
E1a – binds to p110Rb (represses cell proliferation)
E1b – binds to p53 (represses cell proliferation)
Do DNA tumor viruses transform permissive or nonpermissive cells?
NONPERMISSIVE
Which DNA viruses are associated with human cancers?
EBV
HBV
HSV
HPV
The interaction of what two things lead to or contribute to cell transformation?
Interaction of specific viral proteins with products of tumor suppressor genes
ADENOVIRUSES:
- cause GI and respiratory infections in humans
- transform rodents cells (NOT human cells!)
vary in oncogenic potential from high to none
what are the transforming proteins in Adenovirues?
E1a - binds to p110Rb (represses cell proliferation)
E2b - binds to p53 (represses cell proliferation)
only oncogenic in rodents
Papillomaviruses
- majority of genital cancers contain HPV DNA
- supsected cofacters includ tobacco smoke and coinfection with HSV
Viral DNA is episomal in normal tissues, but integrated in cancers and CIN
Transforming proteins:
E6 binds to p53
E7 binds to p110Rb
Polyomaviruses
different types do diff. things in rodents
transforming proteins:
SV-40 - large tumor (T) antigen has domains that bind to p110Rb and p53
1-2 of the 3 polyoma virus T antigens have transforming activity
Herpesviruses
some linked to human cancer:
EBV = linked to Burkitt’s lymphoma and nasopharyngeal carcinoma
proteins invovled in transformation include: EBNA2 (transcriptional transactivator), LMP 1 and LMP 2a and b (tyrosine kinases)
possible cofactors involved = malaria and c-myc proto-oncogene translocation (chrom. 8->14)
HSV-2 and CMV = implicated in cervical cancer and CIN
HHV-8 (KSHV; Kaposi’s sarcoma-associated herpes virus) - cause of Kaposi’s sarcome, implicated in multiple myeloma, contains 16 cellular genes including C-cylin and cytokines.
Hepadnaviruses
75-85% of primary human hepatocellular carcinoma cells carry human Hep B virus (HBV) genes
impaired immunity and alcohol-associated hepatic cirrhosis = co-factors
X-protein interacts with p53
latency period between infection and primary hepatocellular carcinoma = 9-35 years
What are the only diploid viruses?
retroviruses
What kind of RNA do retro-viruses have?
+ sense s-s RNA
Which of the three retrovirus subfamilies has oncogenic potential?
only the oncovirus subfamily. Duh
Lentiviruses cause HIV in people
Spuma viruses = 3rd type
What are the 3 ways that oncogenic viruses can cause transformation in permissive cells?
- introduce oncogenes
- insertional activation or promoter insertion
transcriptional activation
What kind of Virus
- contains a helical nucleoprotein complex inside an icosahedral capsid which is enveloped
- undergoes reverse transcriptase
- genome (as DNA) integrated into host DNA
- cause tumors
- some members carry oncogenes
- HIV-1, cause of AIDS?
this = retrovirus
What morphological type of oncovirus is mature?
Type C
Difference between
EXOGENOUS
and
ENDOGENOUS
type C virusus
exogenous:
- spread horizontally as infectious agents
- when ocogenic, mainly cause tumors of reticluloendothelial system ad hematopoietic systems (leukemia, lymphomas) or conective tissue (sarcomas).
endogenous
- Found in all cells of all individuals of a species
- Viral information – is a constant part of genetic constitution; not pathogenic for host; can be activated by radiation, chemical carcinogens or metabolic inhibitors
Retrovirus Replications invovles:
reverse transcriptase (get DNA copy of RNA) and sticking DNA into host cell DNA
- make mRNA from that DNA, and also make full-length genome of DNA
virual genes invovled in replication = virogenes
Viral-onc:
viral copies of cellular oncogenes invovled in cellular division or differentiation pathways.
Made by:
If virus DNA is integrated into host cell chromosome right next to an oncogene, when it makes the full leng virion + sense RNA, the pol can make a mistake and copy oncogene also. If the virus made from it then enters another cell, will make the product of the oncogene, because the cell is under viral control now, not cell control.
Once product of oncogene is made, the cell is transformed
what is the difference between NON-DEFECTIVE and DEFECTIVE VIRUSES:
when oncogene is formed, sometimes 1 of the viro-genes is left behind and not copied properly, so you get a DEFECTIVE virus.
Non-defective viruses form infectious progeny (leukemia, Rous sarcome) = have virogenes and an oncogene.
Defective viruses have lost part or entire virogene (copie oncogene instead). Require a helper virus to REPLICATE. (Can still infect, but can’t replicate.) They’re acute transforming viruses.
Rous Sarcoma Virus:
one of the non-defective, acute transforming virus - all transforming genes + SRC oncogene
causes sarcoma in chickens
Acute transforming genes:
introduce oncogene which is not downregulated
Mech 1 for transforming cells:
introduce oncogenes into cell that are not turned off - they’re on, and you get transformation.
Done by acute transforming viruses, non-defective and defective
Mech 2 for transforming cells
no oncogenes found here, just virogenes.
Gene inserted into host cell genome -randomly placed in section that normally is down-regulated in the cell.
Virus gets all viro-genes copied, and also happens to turn on a part that starts cell on path to uncontrolled growth.
This is chronic - takes much longer for cancer to appear.
Mech 3 for transforming cells
trans-activator proteins call for their RNA to be made - even tho they’re to activate the virus, sometimes they go and activate cellular oncogenes, causing cellular transformation
(seen in human t-lymphovirus 1)
