The hepatitis B virus is a double-shelled spherical particle with a diameter of 42-47 nm (4). It consists of icosahedral nucleocapsid (protein core) enclosing a circular, double-stranded DNA genome. The outer lipid envelope contains embedded proteins (HB surface antigens) which are involved in viral binding of susceptible cells.
The hepatitis B virus genome is a relaxed circular, partially duplex DNA. This genome is unique in that the minus strand is full length and the plus strand is less than full length, leaving 15-50% of the molecule single-stranded (5). The genome is 3020-3320 nucleotides long (for the full length strand) and 1700-2800 long (for the shorter strand). Its circularity is maintained by 5’ cohesive ends linked to viral DNA polymerase (5).
Shortly after the virus enters the body of a new host, it’s initial response is to infect liver cells. The reason why the virus targets the liver and not any other organ in the body is because liver cells possess specialized receptors that can bind to the viral antigens and subsequently process its DNA.
First the virus attaches to a liver cells membrane via receptors.
The virus is then transported into the liver cell by receptor-mediated endocytosis and uncoats in the cytoplasm (6).
The core particle then translocates it’s contents of virion DNA and DNA polymerase into the hepatocyte nucleus. This DNA is then organized to form a viral mini-chromosome (6).
Once within the cell nucleus, the hepatitis B DNA causes the liver cell to produce, via messenger RNA: Hepatitis B viral surface proteins, viral core proteins, DNA polymerase, and hepatitis B e-antigen protein.
The cell then assembles live copies of the virus. The copies of the virus are released from the liver cell membrane into the bloodstream and from there can infect other liver cells and thus replicate effectively. Assembly within the endoplasmic reticulum is omitted for the sake of simplicity.