Hepatitis A Virus: Structure and Function

Instructor: Erika Steele

Erika has taught college Biology, Microbiology, and Environmental Science. She has a PhD in Science Education.

This lesson will describe the structure and function of the virus that causes hepatitis A. After the lesson, there will be a few questions to test what you have learned.

What Is Hepatitis A Virus?

Viral hepatitis is the most common cause of hepatitis worldwide. Hepatitis A virus is very common in areas of the world with poor sanitation. The disease is easily transmitted to others through blood, the oral-fecal route, anal sex, and contaminated food and water. The virus travels through the bloodstream to the liver where it infects hepatocytes, cells that form the liver's main tissue and make up most of its mass.

Like all viruses, the Hepatitis A virus is simple, made up of only nucleic acid and proteins, but it is still able to take over normal cell functions and convert them to make more viruses. This lesson will cover the structure, replication, and transmission of the virus that causes hepatitis A.

Viral Structure

Viruses contain only what's necessary to allow them to hijack the cells they infect. The nucleocapsid, the core structure of all viruses, contains protein and nucleic acid. The protein portion of the nucleocapsid, called the capsid, coats and protects the virus genome. In some cases, the capsid is also involved in viral entry. Other viruses contain an envelope that aids in cell entry, but also protects the virus from the host immune system. The nucleic acid contains the genes of the virus and can be RNA or DNA. The genome only has the genes needed to shut down the host cell and make more viruses. These features of Hepatitis A Virus (HAV) are described below.

Nucleocapsid

Figure 1:The capsid of the HAV is icosahedral in shape.
Nucelocapsid

Viral hepatitis is caused by a variety of viruses; each coming from different viral families. HAV differs from other hepatitis strains because it's a member of the picornavirus family. Picornaviruses are small, non-enveloped, icosahedron-shaped viruses containing a single strand of RNA. An icosahedron is a 3-dimensional figure with 20 faces resembling a soccer ball. The viral structure is further described below.

Capsid

Figure 2:The capsid of the virus is made of subunits called protomers. Each protomer is made of three proteins.
HepA Protomer

The capsid of HAV is made up of subunits called capsomeres as shown in Figure 2. Each capsomere is made up of five protomers. Each protomer of HAV is made of three proteins; VP1, VP2, and VP3, which have a role in cell entry.

Genome

Figure 3:The genome of HAV is a single strand of RNA that is divided into three sections.
genome

The genome of HAV is positive-sense, single-stranded RNA, written as ss(+)RNA. Because the virus is positive-sense RNA, it can be used as mRNA and converted (translated) into protein upon entering the cell. The genome has an attached protein VPg that acts as a primer for copying the genome (replication).

As shown in Figure 3, the genome is divided into three segments: P1, P2, and P3. The first segment encodes genes to make capsid proteins. The other two segments make other genes needed for replication.

Viral Replication

Figure 4:HAV enters the cell through endocytosis. Replication, translation, and assembly occur in the cytoplasm of infected cells.
Cycle

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