Influenza viruses are about 100 nm in diameter, their outer membrane being the lipid bilayer membrane (elementary cell membrane). On the outer side of the membrane there are glycoproteins, which make the virus stick to the host cell membrane and make it difficult to be recognized by the antibodies. The main glycoprotein here is called Hemagglutinin. It has the shape of a spike, protruding perpendicularly from the viral outer membrane Outer part of this spike searches for the appropriate sugar chains on the host cell membrane and so adheres to the host cell. After the contact is established, the attack on the cell is triggered.
The second protein on the outer viral membrane is called the neuraminidase. It has the enzymatic activity and cleaves the sialic acid residues from the cell glycolipids or glycoproteins. This way it enables the detachment of the newly formed viruses from the host cell (the sialic acid residues are the points of attachment of the virus membrane to the host cell membrane). Neuraminidase is the target of some antiviral drugs.
On the inner side of the viral lipid bilayer membrane there is a coat of the M1 matrix protein which helps the viral RNA to be attached to the inner layer.
Inside the influenza virus there are eight RNA chains, each is accociated with the trimeric RNA polymerase (its three components named the PB1, PB2 and PA). RNA is coated with the nucleoprotein molecules (NP).
Influenza virus contains also the membrane protein M2 which forms a tetramer and functions as an ion channel, regulating the acidity within the virion particle.