Yellow Fever Virus: Structure and Function

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  • 0:03 What is the Yellow…
  • 1:05 Yellow Fever Virus Structure
  • 2:49 Infection Route and…
  • 4:21 Symptoms and Treatments
  • 5:20 Lesson Summary
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Lesson Transcript
Instructor: Amanda Robb

Amanda holds a Masters in Science from Tufts Medical School in Cellular and Molecular Physiology. She has taught high school Biology and Physics for 8 years.

In this lesson, we'll discuss the parts of the yellow fever virus' structure and what functions those parts perform during infection and replication. We'll also learn about symptoms and treatment of the disease that the yellow fever virus causes.

What Is the Yellow Fever Virus?

Imagine coming down with the flu. You get a fever and your body starts to ache. You might feel nauseous or have spells of vomiting. Your head hurts and you shiver and curl up under a blanket, even though your face is covered in cold sweat. Normally, you consume soup or tea or both, perhaps some pain reliever, and recover in a few days. Your immune system fights off the flu virus and you're back to your old healthy self.

However, this isn't always how the situation plays out. Some viruses are far more deadly than those that cause the flu. The yellow fever virus causes acute hemorrhagic disease in which your fever worsens and your internal organs start to bleed, despite the initial symptoms resembling those of the flu.

Risk areas for yellow fever
yellow fever virus risk areas

Yellow fever virus is transmitted through mosquito bites and is mostly prevalent in Africa, although some cases have been recorded in tropical South America. Today, we'll examine the parts of the yellow fever virus' structure and their functions in causing these life-threatening symptoms.

Yellow Fever Virus Structure

Although they are so small they cannot be seen through the lenses of an optical microscope, viruses can be quite deadly. All viruses have a similar structure; all viruses have a genome and a nucleocapsid, and some have an envelope, too.

The nucleocapsid is a protein coat that protects the genome of the virus. A genome is the genetic material of the virus. Some virus' genomes are composed of DNA, while others are made of RNA. Yellow fever virus is a single-stranded RNA virus, meaning only one strand of RNA comprises its genome. Like those of some other viruses, yellow fever virus' envelope is a flexible coat made of lipids, or fats, that cover the nucleocapsid.

Structure of an enveloped virus
viral structure

Yellow fever virus is a type of flavivirus, a small, enveloped virus whose diameter ranges in size from 40 to 60 nm. That means flaviviruses are 40,000,000 times smaller than a centimeter, which is about the width of a small screw.

Yellow fever virus particles under a transmission electron microscope
yellow fever virus

Yellow fever virus has three main types of proteins: E, M, and C proteins. The function of the virus' E proteins is to attach the virus to receptors on host cells; they initiate the biggest immune response from the host. The M proteins appear to keep the E proteins functional during the assembly of new viruses, but M proteins have been studied less than E proteins. C proteins are found in the virus' nucleocapsid.

All flaviviruses have a positive-sense RNA genome, meaning the RNA is in the correct order for the host cell to copy directly to produce protein. It doesn't need to be copied into other forms to be used as instructions for protein.

Infection Route and Replication

Viruses are specific to their hosts. Not all viruses infect all organisms. Yellow fever virus specifically infects humans, particularly liver cells, or hepatocytes. Once yellow fever viral particles reach the liver through the bloodstream, their E proteins attach to the hepatocytes. A hepatocyte brings the virus inside it in a sphere called an endosome, or membrane-bound vesicle. The virus then breaks out of the endosome by fusing its membrane with the endosomal membrane. The virus' RNA genome is then freed into the cell, where host cell machinery copies it to produce protein, creating more viruses.

You might be wondering why a host cell would make more of the thing that is killing it. The virus is clever and tricks the host cell into thinking that the viral RNA is host cell RNA. The cell unknowingly copies the viral RNA in the rough endoplasmic reticulum (ER), a structure made of membranes that produce proteins. From the ER, new viruses bud out, cloaking themselves in the cell's ER membrane. Soon, the host cell contains so many viruses that the host cell dies and the viruses escape to infect other host cells.

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