All viruses are characterized by these structural characteristics. Each virion is composed of an outer capsid consisting of proteins and an inner core of nucleic acid. Keep it simple. Viruses consist of genetic material contained within a protective protein capsid The protein capsid and nucleic acid core can together be referred to as the nucleocapsid. In some viruses an outer lipid bilayer envelope is also present.

Viruses are categorized based on morphology. The capsid may be helical or icosahedral. Furthermore, enveloped viruses cover themselves in a modified form of cell membrane (which they can pick up from the outer plasma membrane of the infected cell or, in some cases, the nuclear membrane or ER.). Some viruses, lastly, are morphologically complex, such as bacteriophages.

Viruses are also categorized based on the type of genetic material they contain, whether it is single or double stranded, and their mode of replication. Viral genomes may be double stranded DNA, single stranded DNA (during part of the life cycle), or RNA. Retroviruses are RNA viruses that replicate through DNA intermediates.

As you learn viruses, keep in mind the primary means of classifying them. Make it a habit to reflect on any new virus in terms of morphology, type of genetic material, and mode of replication.

The WikiPremed MCAT Course is a comprehensive course in the undergraduate level general sciences. Undergraduate level physics, chemistry, organic chemistry and biology are presented by this course as a unified whole within a spiraling curriculum. Please read our policies on Privacy and Shipping & Returns.  Contact Us. MCAT is a registered trademark of the Association of American Medical Colleges, which does not endorse the WikiPremed Course. WikiPremed offers the customers of our publications or our teaching services no guarantees regarding eventual performance on the MCAT.

Creative Commons License
WikiPremed is a trademark of Wisebridge Learning Systems LLC. The work of WikiPremed is published under a Creative Commons Attribution NonCommercial ShareAlike License. There are elements of work here, such as a subset of the images in the archive from WikiPedia, that originated as GNU General Public License works, so take care to follow the unique stipulations of that license in printed reproductions.