Week 3 - Viral Structure, Classification, and Replication - Ziegler Flashcards Preview

Med Year 1 - Foundation > Week 3 - Viral Structure, Classification, and Replication - Ziegler > Flashcards

Flashcards in Week 3 - Viral Structure, Classification, and Replication - Ziegler Deck (37):

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?


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?

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?

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?



What is the cytoplasmic DNA virus?


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

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:


Viral Oncogenes


Describe the differences between non-defective and defective viruses:

-retains virogenes along with an oncogene
-involved in chronic tumors

-Part or all of their virogenes have been replaced by oncogenes
-involved in acute tumors
-require helper virus for replication