Genetics of viruses Flashcards
What are the types of viruses?
- Bacteriophages
- Animal viruses
What are the types of animal viruses?
- Influenza - enveloped virus
- HIV - retrovirus
What genome does animal virus contain?
- Positive-sense RNA genomes -> HIV
- Negative-sense RNA genomes -> influenza
Is the genome of animal virus ss or ds?
single stranded RNA genomes
(+)-sense/ (-)-sense
Which ss RNA genome would translated?
- (+)-sense RNA genome
they are identical to the viral mRNA
What are the structures of influenza?
8 big structures
list starting from the inside to the outside
- (-)-sense RNA genome is segmented into 8 linear ss molecules, each associated with a nucleocapsid protein [(NP) - taken from host cell] , together forming ribonucleocapsid (RNP)
- Each RNP is associated with a viral RNA-dependent RNA polymerase.
- Nuclear export proteins
- Matrix protein (M2)
- Haemagglutinin (HA)
-
Neuraminidase (NA) **
7. Ion channel (M1)** - **Viral envelope **
What are the general steps in the reproductive cycle of influenza?
5 steps after ‘breaking in’
Virus settle on epithelial cells of mucous membrane -> NA break down mucoprotein, aiding penetration of mucous layer
- Attachement
- Penetration and Uncoating
- Replication
- Maturation
- Release
In INFLUENZA
What occurs in Attachment?
Haemagglutinin binds to sialic acid
HA has similar chemical shape to the body’s molecules
In INFLUENZA
What happens in Penetration and Uncoating?
5 steps :(
- Receptor bound viruses taken into cell by receptor-mediated endocytosis, CSM invaginates and pinch off, forming endosome
- Protons pumped into the endosome, acidifying it
- M2 ion channel pump H+ into virion interior.
- As the viral envelope fuses with the endosomal membrane, M1 proteins are released from viral RNPs and RNPs are released into the cytoplasm
- RNPs enter the nucleus of the epithelial cell.
2-4-> uncoating
1- >penetration
In INFLUENZA
What happens in Replication?
5 steps
- In the nucleus, ss (-)-sense viral RNA genome act as template and transcribed into (+)-sense mRNA via viral RNA-dependent RNA polymerase.
- mRNA transported out into the cytoplasm for translation of viral structural proteins (capsid,matrix proteins,glycoproteins) and viral enzymes using host ribosomes
- Newly synthesized viral proteins (HA and NA) transported to golgi apparatus for futher modification and incorported onto CSM.
- Nucleocapsid proteins transported back into nucleus to** bind with viral RNA to form RNPs**.
- (+)-sense mRNA remain in the nucleus to be used as template to** replicate (-)-sense RNA genomes** for new influenza virus.
In INFLUENZA
What happens during Maturation?
(matrix proteins containing) RNPs are transported to sites at the CSM where NA and HA are embedded in.
In INFLUENZA
What happens during Release?
- Mature virus remain bound to sialic acid receptors by haemagglutinin , detaching once their neuraminidase cleaves sialic acid residues from the host cell.
- Mature virus relased via budding.
- Host cell does not lyse immediately
How does lambda phage switch from lysogenic to lytic cycle?
due to environmental trigger (e.g uv light) that activates the virus
What is the steps of adsorption of HIV and host cell?
- Glycoprotein gp120 on the surface of the HIV binds to the CD4 receptor, a cell-surface receptor found on T helper cells and macrophages of the host immune system.
What is the steps for penetration of HIV into host cell.
- Upon binding to CD4, gp120 undergoes a conformational change, allowing it to bind to a co-receptor known as CXCR4 on the surface of T helper cells and CCR5 on macrophages.
- gp41 pulls the virus closer to the host cell. The co-receptor (CXCR4 / CCR5) facilitates the entry of the gp120-CD4 complex through the host cell membrane.
- The HIV envelope fuses with the host cell membrane, releasing the viral contents consisting of viral nucleic acid and enzymes into the host cell.
