A study of protein folds , structures that change little during evolution, in thousands of organisms and viruses, found folds shared across all and only 66 that were specific to viruses. This article is republished from Cosmos. You can access the original post here. Viruses lack many of the features that are the hallmarks of life.
Word Count: Why are viruses considered non-living? Viruses are responsible for some of the most dangerous and deadly diseases including influenza, ebola, rabies and smallpox.
The answer has been a subject of debate since the moment viruses were first named in There is no single undisputed definition of life. Does it multiply through cellular division? Does it have a metabolism? Read more: What came first, cells or viruses? They fail the second question for the same reason.
Unlike living organisms that meet their energy needs by metabolic processes that supply energy-rich units of adenosine triphosphate ATP , the energy currency of life, viruses can survive on nothing. In theory, a virus can drift around indefinitely until it contacts the right kind of cell for it to bind to and infect, thus creating more copies itself.
Scientist agree with the fact that organisms contain levels of organization, the ability to acquire materials and energy, maintain an internal environment, respond to stimuli, the ability to reproduce and develop, and the ability to adapt and evolve to changing conditions. After finding out a little about each one. Viruses are microscopic particles that invade and take over both eukaryotic and prokaryotic cells. They consist of two structures, which are the nucleic acid and capsid.
The nucleic acid contains all genetic material in the form of DNA or RNA, and is enclosed in the capsid, which is the protein coating that helps the virus attach to and penetrate the host cell. In some cases, certain viruses have a membrane surrounding the capsid, called an envelope. This structure allows viruses to become more. There are many living things in our world. However, there are many restrictions for it to be considered a living thing.
Virus is a big part of our lives, and there is a controversy whether it is a living thing or not. I believe that a virus should not be considered living thing because they lack many of the properties that scientists associate with living organisms.
A big reason of why viruses should not be considered. Are viruses alive? Life is the existence of someone such as a human, an animal, or a plant. Life can refer to the ability of an organism to develop, grow, and reproduce. Although all living things have all the reasons to be, all living organisms eventually die.
A recent study has investigated viral origins by analysis of the evolution and conservation of protein folds in the structural classification of proteins SCOP database. This work identified a subset of proteins that are unique to viruses. The authors conclude that viruses most likely originated from early RNA-containing cells.
If viruses made an evolutionary leap away from the cellular form, casting off its weighty metabolic shackles to opt for a more streamlined existence, did they cease to be life? Have they reverted to mere chemistry? They all have surprisingly complex replication life cycles, however; they are exquisitely adapted to deliver their genomes to the site of replication and have precisely regulated cascades of gene expression.
Viruses also engineer their environment, constructing organelles within which they may safely replicate, a feature they share with other intracellular parasites. Fundamental to the argument that viruses are not alive is the suggestion that metabolism and self-sustaining replication are key definitions of life.
Viruses are not able to replicate without the metabolic machinery of the cell. No organism is entirely self-supporting, however — life is absolutely interdependent. There are many examples of obligate intracellular organisms, prokaryote and eukaryote that are critically dependent on the metabolic activities of their host cells.
Humans likewise depend on the metabolic activity of nitrogen-fixing bacteria and photosynthetic plants along with that of our microbiota. There are very few if any forms of life on Earth that could survive in a world in which all chemical requirements were present but no other life.
So, what does define life? Some have argued that the possession of ribosomes is a key ingredient. This draws a neat distinction between viruses and obligate intracellular parasites such as Chlamydia and Rickettsia.
This definition also confers the status of life on mitochondria and plastids, however. The endosymbiosis that led to mitochondria is thought to have given rise to eukaryotic life. Mitochondria have metabolic activity on which we depend, they have machinery to manufacture proteins and they have genomes.
Most would accept that mitochondria are part of a life form, but they are not independent life. I would argue that the only satisfactory definition of life therefore lies in the most critical property of genetic heredity: independent evolution.
0コメント