Viruses Flashcards
What do viruses need to survive?
A host
What kind of nucleic acid can a virus have?
DNA or RNA
What is a bacteriophage?
virus that infects bacteria
What are viruses that do not have envelopes called?
Naked viruses
What kind of organisms do phages infect?
Hosts with cell walls
What is an early gene?
Expressed immediately after infection and includes any special enzymes required to express viral genes
What about a virus determines the specificity of the host it can infect?
the surface of the virus
How is a virus taken into a cell?
Receptor Mediated endocytosis or fusion
Why might antibodies have a hard time accessing a viral capsid?
due to the envelope as it contains host membrane components
What is the outcome of the lytic cycle?
The cell lyses
The early gene in the lytic cycle produces which enzyme?
hydrolase
Which enzyme is transcribed from the lytic cycle late?
lysozyme
What is the phage genome incorporated into the bacterial genome known as in lysogenic cycle?
prophage
What is the host called during the lysogenic cycle?
lysogen
What makes the prophage silent?
phage encoded repressors that bind to phage promoters
What is the outcome of the lysogenic cycle?
prophage activates and excises itself from the host genome. Then enters the lytic cycle
What is an advantage to the lytic cycle?
useful for rapidly increasing numbers but host cells are destroyed
What is a consequence of the lysogenic cycle?
By excising, it may take part of the host genome with it
What is transduction?
process of host genome being packaged with viral genome and can spread to new host. There will be a presence of new DNA
Are animal viruses phages?
no
how do animal virus enter animal cells?
endocytosis
What is the productive cycle of animal viruses?
enveloped virus exits host by budding through but does not destroy cell. The envelope becomes coated with membrane
What is a prophage called in animal cells?
Provirus
Is there a lysogenic cycle in animal cells?
Yes
Do positive RNA viruses need to encode RNA dependent RNA Pol?
yes
What kind of RNA genome does positive RNA viruses have?
single stranded RNA genome
When does translation occur for positive RNA viruses?
upon entrance into cell and acts directly as mRNA. The genome is effective
Negative RNA viruses must carry what polymerase?
RNA dependent RNA Pol and encode it
What is negative RNA a template for?
negative mRNA [roduction
If host ribosomes translate negative RNA what happens?
useless polypeptides are made
Where is the RNA dependent RNA Pol carried in the virus?
The capsid
What results from using negative RNA strand for template of RNA dependent RNA Pol?
Positive RNA strand
Retroviruses encode what enzyme?
Reverse transcriptase
What kind of RNA viruses are retroviruses?
Positive RNA viruses that undergo lysogeny.
What does Reverse transcriptase use?
Use RNA to make DNA
What are the three retroviral genes?
gag, pol, env
What does the gene gag encode?
capsid proteins
What does the gene pol encode?
Reverse transcriptase
What does the gene env encode?
viral envelope proteins
What are subviral particles?
infectious agents smaller and more simple than a virus
What are prions?
Subviral self replicating proteins that are shape based. It is a misfolded version of a protein that all ready exists
What makes prions hard to destroy?
Misfolded proteins are resistant to degradation by chemicals or heat
What makes prion diagnosis difficult?
long incubation periods
What are viroids?
short piece of circular single stranded RNA with excessive self complementarity that does not code for proteins
