TL;DR Q&A on Viruses

In this post, I will briefly answer common questions about viruses. Some of the answers I provide are summaries of information from other sites; these are my “too long; didn’t read” (TL;DR) sections. First the question is presented, then one or more reference links are given; finally the TL;DR box below would have the shortened and brief answer. Some questions and answers can be found abundantly on the internet; therefore I didn’t go the extra mile to put any reference links. Have fun!

Are viruses living organisms, like bacteria?

No, viruses are not alive They do not have any cells. They cannot reproduce (without a living host). They do not produce energy. Although both viruses and [some] bacteria cause infections and diseases, bacteria are living, single-celled (prokaryotic) organisms.

Why do viruses “infect”, and who are their targets?

Introduction to the Viruses (Berkeley University of California Museum of Paleontology)

Viruses infect living host cells for replication purposes. Viruses are basically made of a protein-shell that surrounds genetic material- the blueprints for replication. Viruses do not have the tools necessary for replication, and therefore hijack a living host for those tools. That living host is the cell(s) of an organism.

Do viruses replicate or reproduce?

This PDF I found on Google has a sensible answer. It’s actually four pages from a Biology Glencoe/McGraw-Hill textbook; unfortunately I don’t know which textbook that may be.

Viruses use the host cell to replicate, or create an exact replica of the virus. However, the terms replicate and reproduce can be used interchangeably.

Where did viruses originate from?

Virus — Wikipedia (Section: Origins)
21.1B Evolution of Viruses — Biology LibreTexts
Three hypotheses on origin of viruses — The DONG-A ILBO

There are three hypotheses that explain the origin of viruses:
1. Regressive hypothesis- viruses were parasitic cells (like the bacteria rickettsia and chlamydia) that developed into genes covered in a protein coat. 
2. Progressive hypothesis/escape hypothesis- pieces of DNA and RNA from a larger organism "escaped" and formed a protein coat [that protected them from the outside environment].
3. Co-evolution hypothesis- viruses evolved from complex proteins and nucleic acids during the same time cells first evolved.

What makes viruses different from each other- what is their taxonomy?

This PDF by the Community Colleges of Spokane clearly outlines virus distinction and classification (taxonomy). It also goes further into virus reproduction strategies and other virology topics. (This easily became one of my favorite PDF’s that I found on the internet.) Thanks, Community Colleges of Spokane!

Viruses are classified by nucleic acid/genetic information, presence of a protein envelope, shape, and size. The International Committee on Taxonomy of Viruses (ICTV) is responsible for taxonomy: 
Order (-virales)
Family (-viridae)
Subfamily (-virinae)
Genus (-virus)
Species (-virus)

How do different types of viruses emerge?

Check out this YouTube video by Stated Clearly. It explains how the recent COVID-19 virus possibly emerged.

Sometimes, genetic material from the virus mutates while virus replication takes place in the host cell. The result can be a whole new type of virus, which goes on to replicate as well.

That’s all, folks! I might update this post by adding more Q&A sections, or I’d just start a new one. I hope you enjoyed it; be sure to check out other posts on the site. Don’t forget to stay curious!