5. Viruses(2) Flashcards
What type of virus can integrate into the host rather than escape from it?
Lysogenic viruses
What type of virus escapes host?
Lytic virus
What is the role of repressor proteins during lysogeny?
-Repressor allows the virus genome to be integrated into host chromosome
(Inactivation of repressor results in lysis)
In what phage is the virus genome is integrated into host chromosome?
λ phage
Describe the integration of λ into the host DNA? (3)
-The viral genome integrates at the attachment site attλ (it requires an enzyme, λ integrase)
-Linear double strand injected into host, DNA becomes circular,
sticks together through red complementary overlapping ends
-It creates staggered ends, DNA ligase closes it up
What kind of replication is included in the lytic pathway?
rolling circle replication
Describe rolling circle replication? (2)
- One strand of circle is nicked, a long single-stranded concatamer is made, using the unbroken strand as a template
- A second strand is made, using the single-stranded concatamer as a template, the double-stranded concatamer is cut into genome-sized lengths at the cos sites, giving cohesive ends
What happens to double stranded segments that come off in rolling circle replication?
Pushed into head and assembled into virion
Where else can you come across rolling circle replication?
Genomes of bacteriophages
Where does DNA replication and transcription take place in eukaryotic viruses?
Nucleus
Where does protein synthesis take place in eukaryotic viruses?
Cytoplasm
what does eukaryotic RNA have?
Introns and Exons
Describe the (+) strand RNA viruses of animals? (3)
- Core genetic material is RNA
- Single + strand of RNA encodes everything the virus needs to get started for replication and protein synthesis in host
- Typically these are very small (~30 nm) except coronaviruses
(poliovirus, rhinovirus (common cold), hepatitis A)
Describe a Poliovirus? (3)
- polio has a single linear ssRNA genome
- the genomic RNA also acts as the mRNA but note that there is no capping
- instead the RNA at the 5’ end folds into stem-loops and has a protein, Vpg, bound. This mimics a cap
Describe protein synthesis in a Poliovirus? (3)
- The genomic RNA acts as the mRNA
- Viral protein is synthesised as one large polyprotein- this is a common strategy
- Polyprotein cleaved by proteolysis into different active proteins
Describe Poliovirus replication? (2)
Where does it occur?
- MRNA is copied by RNA replicase
- Genome is (+) strands as it is translated into proteins but when copied complementary strand makes (-) strand
Replication occurs in the cytoplasm
Why does polio have to encode its own RNA replicase?
Why does polio synthesise a polyprotein?
-Host can’t replicate viral genome
