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In total, the influenza virus has 4 types of antigens. Haemagglutinin (HA) and neuraminidase (NA) are found in the outer surface of the particle and the matrix (M) and the nucleoprotein (NP) are found in the inner surface of the particle. It is the type of the nucleoprotein (NP) which determines the type of the virus. There are three forms of the nucleoprotein (NP) and hence there are three main types of the influenza virus.
A lipid envelope forms the outer covering of the particle and two types of glycoprotein are projected from the envelope. They are haemagglutinin (HA) and neuraminidase (NA) which appear as rod-shaped projections of the particle. Haemagglutinin (HA) has two types of subunits, HA1 and HA2 respectively and they are responsible for the attachment of the virus to the receptor protein on the cell membrane. There are 13 major types of haemagglutinin (HA). On the other hand, neuraminidase (NA) is responsible for enzymic properties of the virus and there are 9 main types of neuraminidase (NA). It is also observed that there is a smaller quantity of neuraminidase (NA) surface proteins than haemagglutinin (HA) surface proteins.
The matrix protein (M) is found. The RNA of the virus is related to the nucleoprotein (NP) closely and they form a helical structure. The genome of the virus is segmented and there are 7-8 RNA fragments of ribonucleoprotein (RNP), all of which are needed for replication. (7 RNA fragments for Type C Influenza Virus) Ribonucleoproteins (RNP) are chemically binded to the matrix (M). The matrix protein (M protein) surrounds the nucleocapsid and makes up 35-45% of the particle mass.
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