Anatomy
What are the characteristics of viruses?
You can describe viruses based on a number of features, including:
What they look like (their shape and size).
Genome properties.
Structural proteins and whether or not it has an envelope.
Virus shapes
Viruses can look very different from each other. Scientists often describe them by shape. Types of virus shapes include:
Icosahedral or polyhedral. This is a geometric shape with many sides, similar to a soccer ball. Most viruses that infect people are icosahedral.
Helical. This virus shape looks like a cylinder. Its genetic information is coiled up like a spring inside.
Spherical. Spherical viruses are helical or polyhedral viruses that have an envelope around them. They’re shaped mostly like a ball.
Complex.
Complex viruses combine more than one shape. Viruses that infect bacteria have a polyhedral “head” connected to a helix “body.”
Virus size
All viruses are very small — too small to see without a strong microscope. If you measure them under a microscope, most are between 20nm (nanometers) to 400nm. For comparison, the smallest viruses are about 2,000 times smaller than a grain of sand. They’re about 100 to 1,000 times smaller than the cells in your body.
But their sizes can vary a lot. For instance, the measles virus is about five times larger than Zika virus. Viruses also have varying weights (molecular weight).