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29 Cards in this Set

  • Front
  • Back
Do viruses contain DNA and RNA?
They can contain EITHER DNA or RNA, but not both.
What is the name of the classification system used to describe viruses?
baltimore's classifications
How many classes of viruses are there under the baltimore classification system?

What are they?
There are 6
I: dsDNA
IV: ssRNA+
V: ssRNA-
VI: RNA viruses requiring DNA intermediates for replication
Which class of viruses has the capacity to act as mRNA all on its own?

Which class COULD act as mRNA, but require something else? What is that something else and where is it found?
Class IV: ssRNA +

ClassV: ssRNA - could act as mRNA, but requires RNA dependent RNA polymerase.

This must be found in the virion b/c humans don't have it!
What is an example of a Class VI?
a retrovirus--HIV
What is a capsid made of?

What is its function?
Made of protein structural subunits or capsomers

What are the shapes of a capsid?
icosahedral or helical
Do all viruses have an envelope?

What does the envelope cover?
not all viruses have envelopes

covers the nucelocapsid
The envelope is part host part virus.

Which part is host and which is virus?
Contains host derived phospholipid bilayer

Contains virus-derived proteins and glycoproteins-for attachment and viral fusion
Which is more fragile a naked virus or a one with an envelope?
More fragile= envelope b/c they are inactivated by detergenets--lipid solvents.
What is the function of a matrix (M)protein? Where are they found?
aid in viral structure--found in the inner layer of the envelope
Where are F proteins found and what do they do?
on the envelope surface--cause viral membranes to fused cellular membranes
How many DNA families of viruses are there?


13 RNA
What determines physiochemical classification of human viruses? (5)
• Chemical nature of the nucleic acid
• Symmetry of the nucleocapsid
• Presence of an envelope
• Dimensions of the virion and capsid
• nucleic acid sequence similarities
What are the steps of viral entry?
Attachment to the host cell

Entry of virus into the host cell

Synthesis of viral proteins and genome

Assembly and release
In the eclipse phase of synthesis are there infectious particles inside? outside?

What about during the latent stage?
eclipse: no infectious particles INSIDE host cell; none outside

Latent: infectious particles are inside the host cell. None outside

after latent phase can detect extracellular virus particles.
What is a protease need for?
viruses can produce a big mRNA which can produce a big polyprotein and then proteases are needed to cleave into smaller proteins.

This conserves energy!!
What are the two ways that viruses are released?
burst--kill infected cell

slow release: membraned or enveloped viruses that bud from the host cell. budding doesn't harm the host cell.
What is the most important factor in virus attachment?
presence of viral receptors on the cell surface is the most important determinant of host specificity.
What receptor is needed for H. influenza a and b virus?

sialic acid


I don't think she's actually going to ask...just good cross review
How do enveloped viral cells enter the host cell?
ONE way: fusion of viral and cell membranes mediated by viral F protein

ANOTHER WAY: phagocytosis and fusion of the viral membrane with the membrane of phagosome (or endosome)mediated by a viral F protein.
What must precede protein synthesis in cells infected with DNA viruses?
synthesis of viral mRNA
What do most DNA viruses depend on?
cellular RNA polymerase II, the enzyme that produces cellular mRNA.
What is a retrovirus?
• Retroviruses are RNA viruses, but their genomes are reverse transcribed into DNA and RNA pol II produces mRNA.
What transcribes Poxviruses?
• Poxviruses are transcribed by viral DNA dependent RNA polymerase and viral accessory proteins. This process is an exception.
What does the synthesis of viral proteins require? viral messenger RNA and host machinery?
viral messenger RNA and host machinery
Are naked ssRNA- and dsRNA infectious?
No, they do not have the enzymes needed to produce ssRNA +.
Do ssRNA + carry a viral RNA polyerase in the viral particle?
No, they don't need it. The proteins translated from ssRNA + will produce the enzymes it needs.

Therefore ssRNA + is infectioous on its own
Is the release of viruses by bursting a host cell more common in naked or enveloped viruses?
in naked