Microbiology
Summary
Hepatitis B virus (HBV) initiates its life cycle by binding to hepatocytes using proteoglycans on the cell surface. Upon entry, the virus's partially double-stranded DNA is converted into a crucial form known as covalently closed circular DNA (cccDNA) through a process termed genome repair. The host cell's machinery, specifically RNA polymerase, then transcribes this cccDNA into four RNA intermediates. Two subsets of these, the subgenomic RNA (sgRNA) and pregenomic RNA (pgRNA), are crucial for producing core protein, viral polymerase, and surface antigens.
Within the hepatocyte, the pgRNA and the viral polymerase are packaged by the core protein, forming an immature viral core. Within this core, the viral polymerase converts the pgRNA back into viral DNA. This immature core is transported to the nucleus, where the viral DNA undergoes processes similar to cccDNA formation and transcription. Following these nuclear activities, the viral core acquires an envelope from the host cell organelles, maturing into an infectious viral particle. Notably, the hepatitis delta virus (HDV) leverages the HBV surface antigens to facilitate its own entry, assembly, and exit from hepatocytes.
Lesson Outline
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FAQs
The envelope of hepatitis B virus plays significant roles in the viral life cycle. It is primarily involved in ensuring successful entry of the virus into susceptible host cells. The envelope's surface antigens interact with specific receptors on the cell surface, allowing the virus to bind and gain entry into the cell.
HBV's viral polymerase plays a critical role in the replication of the virus. After the virus enters the host cell, the viral polymerase reverse transcribes the virus's RNA to DNA (specifically covalently closed circular DNA). This is a crucial step in enabling the virus to integrate into the host's genome and continue its life cycle.
HBV's covalently closed circular DNA (cccDNA) is integral for the viral replication phase. Once the viral genome is reverse transcribed into cccDNA by the viral polymerase, it takes up residence in the nucleus of the host cell. It acts as a template for transcription of sub-genomic RNA and a new round of viral replication, aiding in the perpetuation of chronic infection within the host.
Hepatitis delta virus (HDV) is a unique virus that requires hepatitis B virus for its replication and survival. Co-infection with HDV can complicate hepatitis B infection, leading to more severe liver disease, including accelerated progression to cirrhosis. Effective management of hepatitis B infection therefore also results in control of HDV.
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