Introduction to Viruses
What are Viruses Made Of?
Viruses are particles of nucleic acid surrounded by a protective protein coat; some viruses also have a membranous outer layer containing lipids. Genetic material consisting of the nucleic acid DNA or RNA makes up the core of a virus. The nucleic acid contains the genetic code that holds the instructions to make more copies of the virus. The nucleic acid core is surrounded by a shell made of protein, called a capsid, surrounds the genome and protects the genetic information. In addition to capsid proteins, other proteins may be included in a virus particle to facilitate its entry into cells and aid the early steps of replication.
Certain viruses have an outer membranous layer, called an envelope, that is derived from the lipid bilayer of the host cell and into which viral glycoproteins (proteins that are covalently linked to carbohydrates) are inserted. Key proteins on the envelope surface help these viruses recognize and invade their hosts. Examples of viruses with envelopes are HIV and influenza.
The diagram illustrates the structure of an enveloped virus particle (in cross-section). The genetic material is shown in the center in black. The capsid, composed of multiple copies of the same protein, is shown in red. And an envelope studded with viral glycoproteins (yellow) is present at the outer surface.
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Video and transcript courtesy of Wah Chiu, PhD, National Center for Macromolecular Imaging at Baylor College of Medicine. Funding for the video provided by NCMI, NIH.