Hepatitis B Virus: Structure and Function

Instructor: Jeremy Battista
Hepatitis B is part of a family of similar viruses that affect the liver. It can be deadly, but is often treatable, and for the past 30 years we've had a vaccine for it. This lesson will further explore the structure and function of the hepatitis B virus.

What Is Hepatitis B?

The hepatitis B virus (HBV) is a virus of the hepadnavirus family that causes hepatitis B, an infection of the liver. HBV is generally transmitted between people through bodily fluids, such as blood, semen, and vaginal fluids. Dirty needles from drug use can also easily spread the disease, as can dirty needles from non-sterile tattoo shops. The latter problem here is less common, as more tattoo shops have moved to better cleaning standards thanks largely to stricter regulations. Unprotected sex is another prime way the virus can spread--again, through bodily fluids.

While it might seem like a scary virus, HBV cannot spread through holding or shaking hands, sneezing, coughing, and so forth. Even sharing cups and utensils won't spread the virus. As long as someone steers clear of dirty needles and unprotected sex, and otherwise avoiding contact with bodily fluids, the risk of HBV transmission and infection is low.

Symptoms and Complications of Hepatitis B

The HBV virus most often causes issues with the infected person's liver, often leading to a yellowing of the skin called jaundice. Vomiting, a feeling of extreme tiredness, and dark urine can also occur. What infected persons often feel are typical flu-like symptoms of infection. In more severe cases, people may develop bigger problems, such as cirrhosis of the liver and liver cancers. In rare cases, people can die from hepatitis B complications, but antiviral medicines and other drugs known as interferons are typically effective at treating the infection.

Structure of the Virus

The viral structure of hepatitis B is similar in many ways to other viruses. In the core of the virus is the genetic material, DNA, and the enzyme DNA polymerase, which are surrounded by a capsid (a protein shell). The entire virion (virus structure) is then surrounded by the envelope.

hHBV structure

Now let's explore each of these components. The DNA is the blueprint for the virus. It provides a recipe for making more of the viruses upon infection of the host cells. As it begins to copy itself, it uses an enzyme, DNA polymerase, to create more DNA strands. This helps it infect and attack other cells.

The capsid that covers the DNA is a protector, keeping out anything that would destroy the DNA. The shape of it is referred to as icosahedral, which means it's a 20-sided polyhedron. The capsid of HBV is unique in that is carries HBcAG, or the hepatitis B core antigen. This is a special protein that helps the virus replicate and indicates that, indeed, replication is occurring.

Holding and protecting the virus is the envelope. It works to protect the virus from all of the exterior elements that could destroy it. The envelop contains additional hepatitis B surface antigens that come in the form of small (S-HBsAg), middle (M-HBsAg), and large (L-HBsAg). These antigens help to detect and attach to host cells.

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