How are viruses and cells similar?


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There are a number of similarities between viruses and cells. Both are too small to be seen with naked eyes and require a microscope for observation. Both contain genetic material, in the form of DNA and/or RNA. Both of them can replicate, that is, produce more organisms similar to themselves. Both of them are capable of causing diseases to other life forms.

The differences between the two far outweigh the similarities. For example, bacteria contain both DNA and RNA, while the viruses contain either DNA or RNA. Bacteria can replicate on their own and are capable of performing all the functions of living organisms. In comparison, viruses are not even considered living organisms. They require a host cell to carry out life processes, such as replication and carrying out genetic instructions, etc. Bacteria are relatively bigger in size than viruses.

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How are cells different from viruses?

To understand how cells are different from viruses, one must first understand what a virus is and how it functions. A virus is a small particle that exists as a capsid, which is generally defined as a protein coating that contains and protects the genetic material located inside. Viruses can only function inside a host cell, and while outside of a cell they lack the ability to generate the metabolic activity necessary for protein production and replication. Once a virus infects a host cell, it inserts its own genetic material, in the form of DNA or RNA, into the host cells genetic material, causing the host cell to create many copies of the virus, instead of the necessary proteins for healthy cell function and survival. These new viruses then leave the host cell, causing it to die, and go on to infect more cells. 

The main difference between a cell and a virus is that a cell, whether it is prokaryotic or eukaryotic, is metabolically active, and maintains all the necessary functions for self-replication. This is not possible in viruses. Cells are also different from viruses due to the presence of ribosomes, which are responsible for the process of protein synthesis. Various cell types can also contain many other organelles that are not present in viruses. Also, cells contain a cell membrane to hold in the cytoplasm and all of the components of the cell contained within it, while viruses, other than their external capsid protein coat, lack this feature. From an anatomical stand point cells are also much larger than viruses. 

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How are cells and viruses alike?

Cells and viruses are alike in several categorical as well as conceptual ways; meaning, they can be considered in terms of "have/have-not" components and properties, as well as ways that they behave which humans ascribe qualitative value to (such as what we consider to be "alive").

Cells and viruses both use nucleic acids to store their genetic information, and they encode this information in the same way; with specific, compatible nucleotide bases, organized into genes. Both use the same protein production "machinery" in order to transform this information into a metabolic product; specifically, they both use RNA as a "blueprint" for ribosomes to follow when making a protein. Both require energy in order to achieve this; in the case of the virus, it simply uses the cell's energy.

I would consider both cells and viruses to be evidence of life; cells obviously, but viruses because they depend upon things we consider to be "living" in order to complete their own "life" cycles. If we found a virus on Mars, I think most scientists would cautiously consider this to be evidence of life, even if that life wasn't immediately discovered. 

They are also alike in that we have no fossil record of their origins, nor the ability to synthetically create them at present. This leaves significant questions about how and when they formed, and to what degree their modern forms and properties are representative of their origins. 

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