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Hepatitis B virion (a member of the Hepadnavirus family), also known as the Dane particle, has an outer lipid envelope and an icosahedral nucleocapsid protein core which consists of a viral DNA and a DNA polymerase with reverse transcription like retroviruses. The embedded proteins of the outer envelope bind the viruses with the susceptible cells for their entry. With a diameter of 42nm, it is the smallest among all other enveloped animal viruses but also exists in a pleomorphic form with filamentous, spherical bodies missing a core. These non- infectious particles are made out of the proteins and lipids that structures some portions of the surface of the virion, which is known as the surface antigen (HBsAg), and is delivered in overabundance amid the virus's life cycle.

It consists of HBsAg, HBcAg, HBeAg, Hepatitis B virus DNA polymerase, HBx.

HBx protein’s function is not well known, but some evidence implies that it aids in activating the process of viral transcription.

The HBV genome has an unusual circular DNA, as the DNA isn’t completely double-stranded. The viral DNA polymerase is attached to one end of the full-length strand. The full-length strand is 3020–3320 nucleotides long and the short length-strand is 1700–2800 nucleotides long. The non-coding strand is complementary to the viral mRNA. After infection of the cell, the viral DNA is found in the nucleus. The partially ds DNA is rendered to a complete ds by the fruition of the coding strand and expulsion of a protein particle from the non-coding strand and a short succession of RNA from the coding strand. Non-coding bases are expelled from the closures of the negative strand and the finishes are re-joined. The four genes coded by the genome are: C, X, P, and S. Gene C (HBcAg) encodes the core protein whose start codon comes before an upstream AUG start codon, which produces the pre-core protein. HBeAg is delivered by proteolytic handling of the pre-core protein. Gene P encodes the DNA polymerase. The surface antigen (HBsAg) is encoded by gene S is the quality that codes for. Although the HBsAg gene is a long open reading frame, it, however, contains three "start" (ATG) codons that separate the gene into three parts: pre-S1, pre-S2, and S. In light of the various start codons, polypeptides of three unique sizes called huge (from the surface to within: pre-S1, pre-S2, and S), center (pre-S2, S), and little (S) are delivered. The role of the protein coded by gene X is not completely analyzed but rather it is related to liver malignancy which incites genes that engenders cell development and deactivates growth factors.

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