Viruses Flashcards
What are the basic components of a virus?
Genome - contains DNA or RNA.
Capsid - made up of capsomeres.
Nucleocapsid = genome + capsid.
The nucleocapid +/- an envelope is known as a virion.
What are the 7 stages of a viral lifecycle?
Attachment. Penetration. Uncoating. Replication. Assembly. Maturation. Release.
What are the 3 ways in which viral penetration can occur?
Viral translocation:
> Virus translocates across the plasma membrane.
> Naked viruses only.
Surface fusion:
> Viral envelope fuses with the plasma membrane.
> Enveloped viruses only.
> pH independent process.
Receptor mediated endocytosis:
> Naked & enveloped viruses.
> pH dependent process.
> Virion binds to cell receptor > endocytosis > fusion with lysosome > decreased pH leads to uncoating & release into cytoplasm.
What enzyme is needed for the transcription of DNA viruses?
DNA-dependent RNA polymerase.
What is the aim of transcription?
To form mRNA.
What enzyme is needed for the transcription of SS (-) RNA or DS (+/-) RNA viruses?
RNA-dependent RNA polymerase.
What enzyme is needed for the transcription of SS (+) RNA viruses?
None, it acts directly as mRNA.
Does the mRNA have to be sense or anti-sense in-order for translation to occur?
(+) sense
What enzyme is required for viral DNA replication?
DNA-dependent DNA polymerase.
Explain how SS (+) RNA retroviruses are replicated?
SS (+) RNA > SS (-) DNA by RNA-dependent DNA polymerase > DS (+/-) DNA by DNA-dependent DNA polymerase > DS (+/-) > SS (+) RNA by DNA-dependent RNA polymerase.
Explain how SS (-) RNA viruses are replicated?
SS (-) RNA > SS (+) RNA by RNA-dependent RNA polymerase > SS (+) RNA > SS(-) RNA by RNA-dependent RNA polymerase.
Explain how DS (-/+) RNA viruses are replicated?
DS (-/+) RNA virus > DS (-/+) RNA virus by RNA-dependent RNA polymerase.
What is a retrovirus?
A SS enveloped RNA virus that forms DNA from RNA using reverse transcriptase. It then incorporates its DNA into the host cell genome using an integrase enzyme.
How do naked viruses release from the host cell?
Released due to cell lysis - viral multiplication inhibits cell survival signals.
How do enveloped viruses release from the host cell?
The nucleocapsid merges with the plasma membrane > acquires an envelope from the plasma membrane > released by exocytosis.