Week 3 - Viral Structure, Classification, and Replication - Ziegler Flashcards
What is a virion? What are its components?
the infectious virus particle
-Contains genetic material surrounded by a protein coat (capsid)
some viruses also have a lipid and glycoprotein envelope
What does positive or negative polarity mean in reference to a viral genome?
+ polarity: Can immediately be translated into a protein as if it were mRNA
- polarity: Must make a complimentary strand of RNA from the original RNA genome in order to translate it
Where do VAP’s attach on naked viruses and enveloped viruses?
Naked virus - on the capsid
Envloped - on the envelope itself
(becuz its gotta be on the outside)
What is a viral peplomer?
Its a glycoprotein that acts as a VAP. IT sticks out of the viral membrane’s bilayer to interact with where it wants to attach.
Virus infections that yield new infections?
productive
latent is non-productive
Phases of virus multiplication:
1) attachment
2) penetration
3) uncoating
4) virus component synthesis
5) assembly
6) release
Give an example of a cytopathic effect caused by a virus
One example is the Herpes virus. After infecting the host cell it causes it merge with neighbors creating a big multinucleated cells. These can easily be seen in a smear of the infected cells.
What is the goal of an antiviral?
STOP mutliplication
Why can viroporins really rain on a cell’s parade?
They are small virus-encoded proteins that can actually cause hydrophilic pore to open in the host cell’s membrane. This ruin’s the cell’s Ca and H+ gradients and the cell’s whole day in general.
How do virion’s generally exit the host cell?
They usually form a bud and pinch off to form a free infectious virion.
What’s the difference between the latent period and the eclipse period in the virus growth cycle?
Latent period = amount of time it takes before virions are released extracellularly
Eclipse Period = amount of time before virions are produced inside the cell
RNA virus replication occurs where?
CYTOPLASM except orthomyxoviruses (influenza) and retroviruses (HIV) occur in the NUCLEUS
Positive or negative sense RNA viruses have envelopes?
All negative-sense RNA viruses are enveloped
Spontaneous mutations in RNA viruses are more common than in DNA viruses because:
their RNA polymerase are not as accurate in duplication
How do RNA viruses produce individual peptides from polycistronic RNA since this is not a property of eukaryotic cells?
- Viral proteases can cleave larger proteins
- many initation and termination signals can lie within the viral RNA
- Orthomyxoviruses and retroviruses have segmented DNA, each segment cooding for 1 or 2 proteins
DNA virus replication occurs where?
THE NUCLEUS
except poxviruses replicate in the CYTOPLASM
For DNA virus replication to occur, what host functions must work properly?
The S Phase is needed to make things work
Can DNA viruses transform cells?
YES. All of them can except for parvovirus
Hepadnaviruses have a partially double-stranded DNA genome. Describe some specifics about this:
- replicate their DNA in the nucleus via a RNA intermediate
- involve a RNA-dependent DNA polymerase (reverse transcriptase) in their replication
- Can transform cells
REMEMBER: They can be treated with the same antiretrovirals as HIV, because of reverse transcriptase
Parvoviruses have what kind of DNA genome?
Single-stranded
What is the cytoplasmic DNA virus?
Poxviruses
They actually synthesize their own envelope, and provide their own mRNA and DNA synthetic machinery
What does cellular transformation mean?
Some RNA and DNA viruses cause a stable, inheritable change result in poor or no control of cellular division
Do DNA or RNA viruses transform permissive of non-permissive cells?
DNA tumor viruses lyse permissive cells and ONLY transform non-permissive cells
RNA tumor viruses transform both permissive cells & nonpermissive
(They can also carry the actual oncogenes responsible for transformation)
What virus is responsible for human gentital tumors and squamous cell carcinoma?
Human papillomavirus
EBV virus is responsible for what human cancers?
nasopharyngeal carcinoma
African BUrkitt’s Lymphoma
B-cell Lymphoma
What virus causes cervical carcinoma?
herpes simplex type 2
What cancer is caused by Hepatitis B virus?
Hepatocellular carcinoma
HTL virus causes what human cancer?
Adult T cell leukemia
The two important breaks in the cell cycle that cuase big problems with cancer when they get messed up:
P53 – when activated, turns on kinases which phosphorylate the master protein and stops cell cycle from going crazy
P-110
pRB protein, when it is phosphorylated it is the MASTER break in the cell cycle, keeps uncontrolled growth from occurring
Cell oncogenes stem from?
Mutated form of normal cellular genes (proto-oncogenes. Its just the abnormal regulation or expression that cuases BIG problems
Viral oncogenes
Copies of cellular oncogenes that have been acquired by viral genomes during replication, can be introduced to create cellular transformation
Outline the:
tumor virus/host cell interaction.
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
Explain Hepadnaviruses’ link to cancer:
- 75-85% of liver cancers carry Hep B virus
- alcohol-associated cirrhosis and imparied immunity are cofactors
- X-protein interact with p53
- Can have LONG latency period
Three mechanisms by which viruses can cause transformation:
-Introduction of oncogenes
-insertional activation or promoter insertion
(viral promoters on a cellular oncogene
-transcriptional activation
(transactivator proteins like TAX protein enhance transcription of viral and cellular genes)
What sub-family of retrovirus can transform cells?
Onco viruses - Types B, C, and D
this means that lentiviruses like HIV cannot do this
Viral genes involved in replication are called:
Cellular oncogenes that become part of the viral gemome:
Virogenes.
Viral Oncogenes
Describe the differences between non-defective and defective viruses:
Non-defective
- retains virogenes along with an oncogene
- involved in chronic tumors
Defective
- Part or all of their virogenes have been replaced by oncogenes
- involved in acute tumors
- require helper virus for replication
