Summary
Non-cellular infectious particles of genetic material in a protein coat that reproduce only inside host cells.
In depth
Viruses are obligate intracellular parasites, typically 20 to 300 nm, made of DNA or RNA and a capsid, sometimes an envelope. They lack metabolism and ribosomes. Hosts include all cellular life.
Classification uses nucleic acid type (Baltimore classification), shape and host range.
Viruses show host specificity from receptor use. Without ribosomes, they hijack host machinery. They are classed by genome type: dsDNA, ssRNA positive or negative, retroviruses.
Common mistake: viruses are not killed by antibiotics, and are not usually called living because they lack metabolism.
Frequently asked questions
What is Viruses?
Non-cellular infectious particles of genetic material in a protein coat that reproduce only inside host cells.
Which area of biology covers Viruses, and how advanced is it?
Viruses is one of the 52 topics in Immunology & Disease. It is rated Beginner, so it suits learners who are starting out in biology. Related topics in this area include Virus Structure, Bacterial vs Viral Infections, Retroviruses.
Can you give an example of Viruses?
Bacteriophages infect bacteria; SARS-CoV-2 is an enveloped RNA virus.
What should I learn before Viruses?
Viruses is a Beginner topic, so no earlier topic is required. Other Beginner topics in Immunology & Disease that pair well with it include Immune System, Innate Immunity, Adaptive Immunity.
What topics are related to Viruses?
The closest topics to Viruses are Virus Structure, Bacterial vs Viral Infections, Retroviruses, Viral Replication Cycle. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Viruses?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Viruses. To practise the whole of Immunology & Disease, use the Immunology & Disease quiz.
How is Viruses different from Virus Structure?
Viruses: Non-cellular infectious particles of genetic material in a protein coat that reproduce only inside host cells. Virus Structure: A nucleic acid genome enclosed in a capsid, sometimes with an outer lipid envelope and spike proteins. Read both side by side and note what each one explains.
What is a common mistake about Viruses?
Viruses are not killed by antibiotics, and are not usually called living because they lack metabolism.
How should I study Viruses step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Virus Structure and explain the difference aloud. Finally, take the Immunology & Disease quiz and come back to this page for any question you miss.