Question

1a)Describe the structure of the flu virus capsid and the type of nucleic acid enclosed within the capsid. What else is contained in the capsid?

1b) How does the flu virus replicate its genome?

Answer 1

The flu virus also known as Inluenza virus is typically spherical,with a diameter of 80-120 nm but pleomorphism is common.The virus core consists of ribonucleoprotein in helical symmetry.The negative sense single stranded RNA is segmented and exists as 8 pieces.The nucleocapsid is enveloped which has an inner membrane protein layer and outer lipid layer.The membrane protein consists of two components M1 and M2.Protein part of the envelope is virus coded and the lipid layer is derived from modified host cell membrane.There are two types of spikes projecting from the envelope: hemagglutinin and neuraminidase peplomers.

Within the capsid is the single stranded RNA which is segmented and exists as 8 pieces.RNA dependant RNA polymerase is also present which helps in the transcription of viral RNA in the host cells.

Replication of Viral genome:

The virus enters the host cells and bind to the glycoprotein or glycolipid receptors on the host with the help of the spikes.Later the virus changes the shape and fuses with the endosomal membrane of the host.In the host nucleus the virus undergoes primary transcription and produces proteins and the enzymes required for the replication.This is followed by the synthesis of 8 positive complementary sense RNA strands from negative sense RNA segments.A negative sense RNA is produced from this cRNA which is transported to the cytoplasm of the host cell.The virus particles are then assembled to form complete viruses.