Are Viruses Actually a Life Form?

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not even be alive unlike other disease  carrying agents like bacteria protozoans and   fungi viruses occupy a hazy region between life  and non-life which side of the line they fall on   depends entirely on who you ask it is a fierce an  ongoing debate one which raises one of the most   fundamental questions in biology what even is life  anyway so is a virus a life form let's dive in   shall we to understand whether viruses are alive  or not we must first understand what a virus even   is while viral diseases like smallpox rabies polio  and influenza have been with us since the dawn of   humanity it's only very recently that scientists  have come to understand the peculiar pathogens   which cause them following the development of the  germ theory of disease by robert cougley pasteur   and others in the mid-19th century scientists  embarked on a quest to hunt down and isolate   the bacterial agents responsible for every known  disease among these was tobacco mosaic disease an   affliction which stunts the growth of tobacco  plants and causes their leaves to develop a   mottled mosaic-like pattern in 1892 russian  botanist dmitry ivanovsky ground up the leaves   of infected tobacco plants and passed the sample a  porcelain filter whose pores were too small to let   even bacteria through he then used the filtered  sap to inoculate uninfected plants to his surprise   the plants still developed the disease bionovsky  concluded that the disease was caused by some kind   of chemical toxin which could pass through the  filter but he didn't pursue the matter any further   six years later dutch microbiologist martinez  bearing repeated diebanovsky's experiments and   confirmed his puzzling results however he also  took the experiment a step further after infecting   one plant then it ground up its leaves filtered  the sap and used it to infect another plant   and so on and so forth if the infectious agent  was a toxiny reason then its potency would be   reduced as it was diluted from plant to  plants but no matter how many times he   transferred the disease it remained as infectious  as before her first bearing simply assumed that   the infectious agent was simply an incredibly  small bacterium but no matter how hard he tried   he cannot get it to grow on a nutrient medium  the standard method for culturing bacteria in the   laboratory it was also impervious to alcohol which  killed nearly all known bacteria strangers still   the agent whatever it was only seemed to grow and  multiply in the presence of other dividing cells   baffled as to what this age could be bearing dubs  it contagium vivieum fluidum or contagious living   fluid and later filterable virus after an old  word meaning toxin over the following decades   scientists would discover many more viruses using  the porcelain filter method including a pathovirus   the cause of foot of mouth disease in 1898 and  the yellow fever and rabies viruses in 1932   but the first major breakthrough in understanding  what viruses actually were came in 1935 when   american chemist wendell stanley determined  that the tobacco mosaic virus was a particle   not a fluid like bayern could hypothesized and was  composed entirely of protein stanley even managed   to purify the virus particles into needle-like  crystals which could be stored indefinitely on   the laboratory shelf without losing any of  their infective potency this discovery sent   shock waves through the scientific community  as a 1914 new york times article reported   when dr wendell stanley of the rockefeller  institute's princeton station crystallized   the virus which produces the mosaic disease of  tobacco there was a great hullabaloo among the   biologists and rightly so were these crystals  alive apparently no more so than diamonds glass   sand or other crystals with which we are familiar  yet when virus crystals were put on a tobacco leaf   the mosaic disease spread like a slow fire over  the whole field just as if it had been infected   by living bacteria stanley's discovery which won  in the 1946 nobel prize in chemistry seemed to   deal a death blow to the centuries-old doctrine of  vitalism which held that organisms contains arms   order vital essence or divine spark which made  them come alive the chemical hypothesis of life   by contrast held that life was simply a chemical  process like any other and stanley's discovery   that an apparently inner protein particle that  could multiply and spread like a living organism   seemed to confirm this but many mysteries  remained in the same year as stanley's discovery   the invention of the electron microscope allowed  viruses to be directly observed for the first time   and revealed why they had eluded microbiologists  for so long most virus particles are on the order   of 100 nanometers across that's 10 to 100 times  smaller than the average bacterium and too small   to be seen using a regular light microscope but  this did not explain how a mere protein particle   could behave as though it were alive yet be  unable to grow in a laboratory environment   in 1926 american biologist thomas rivers proposed  an explanation stating in a presentation before   the society of american bacteriology that viruses  appear to be obligate parasites in the sense   that their reproduction is dependent on living  cells in other words viruses did not reproduce   on their own via cell division like bacteria  protozoans fungi and other microorganisms but   instead they hijack the molecular machinery of  other living cells to produce more virus particles   but how did viruses accomplish this hijacking  as it turned out a major piece of the puzzle   was still missing as later research by wendell  stanley revealed the tobacco mosaic virus was not   in fact composed only of protein but also of  ribonucleic acid or rna in the 1930s and 40s   a great scientific debate raged over the agent of  heredity which allowed genetic traits to be passed   down from one generation of organisms to the next  while the laws of heredity had been discovered by   czech monk gregor mendel in the 1860s and refined  by american biologists thomas hunt morgan and   herman mueller in the 1910s the specific molecule  which encoded and transferred genetic information   remained unknown some scientists suspected nucleic  acids like rna or its cousin deoxyribonucleic acid   or dna to be the agent of heredity most believe  the more likely culprit to be proteins which were   far more complex than nucleic acids and could thus  store more genetic information viruses would play   a key role in determining which hypothesis was  correct in 1952 american bacteriologists alfred   hershey and martha chase conducted a series of  now classic experiments using t2 bacteriophages   viruses that infect the bacterium e coli at this  point it was known that viruses inject one part   of themselves into the host cell leaving the other  part behind but the question remained was it the   nucleic acid or the protein which was injected  to find out hershey and chase first cultured a   batch of viruses in a cell medium tagged  with radioactive sulfur which would   only be incorporated into the protein of the  virus the next batch of viruses was cultured   in radioactive phosphorus which would only be  incorporated into the nucleic acid both virus   batches were then allowed to infect clean e  coli cells and the resulting cultures spun   in a centrifuge to separate the infected cells  from the discarded non-coding part of the viruses   when hershey and chase measured the radioactivity  of the infected cells they discovered that those   tagged with phosphorus were radioactive whilst  those tagged with sulfur were not this confirmed   that it was the nucleic acids not proteins  which the viruses injected into the cells   subsequent work by scientists such as rosalind  franklin james watson and francis crick would   go on to reveal the structure and function of  dna and rna starting a genetic revolution that's   still shaping the world to this very day today  it's understood that all viruses consist of two   basic components a strand of nucleic acid like  rna or dna encased in a protein coat or capsid   or as british biologist peter meadow or eloquently  put it a piece of bad news wrapped up into protein   viruses come in all shapes and sizes ranging  from 27 nanometers for the poor science circa   virus to 1.5 micrometers for pithovirus and from  long and tubular like the tobacco mosaic virus   too spherical like coronaviruses in addition to  their protein coats many viruses also incorporate   a lipid envelope derived from their host cell  membrane the life cycle of the virus begins when   it enters a host and makes contact with its  cell membrane if the cell is susceptible to   said virus then the virus latches on and like a  miniature syringe it injects its genetic material   along with a number of enzymes into the cell  cytoplasm leaving the capsid behind once inside   the genetic material begins the nefarious process  of taking over the cell's metabolic machinery and   converting it from an independent organism into a  tiny biological factory with a single purpose to   produce more virus particles viruses accomplish  this hijacking in several different ways in dna   viruses the virus's genetic material takes the  place of the cell's own dna and uses the cell's   own enzymes to transcribe this invasive genome  into messenger rna or mrna this mrna is then   read by cellular organelles known as ribosomes  which use its genetic instructions to assemble   amino acids into proteins only instead of the  regular proteins normally used by the cell to   keep itself running the ribosomes now produce  components for new viruses rna viruses on the   other hand contain mrna that is directly read by  the ribosomes skipping the dna transcription stage   entirely and yet a third variety of viruses known  as retroviruses pull off an even neater genetic   trick retroviruses which include hiv contain an  enzyme called reverse transcriptase which takes   the viruses rna and incorporate it into the host  cell's own dna this embedded viral genome known   as a provirus can remain dormant within the  host's genome for a long time invisible to   the immune system and passed along from cell to  cell as they divide and multiply they can then   spontaneously reactivate causing the cells  to start producing the virus again this can   make infection by retroviruses very difficult to  combat but the importance of retroviruses goes   far beyond human disease a full eight percent of  the human genome consists of pro viruses acquired   throughout our long evolutionary history and  as we shall see these genetic hitchhikers have   had a significant and under-appreciated impact  on the development of life on earth once the   new virus particles are assembled they must then  escape the host cell for many viruses that infect   bacteria and other single-celled organisms this is  accomplished via the lytic cycle in which the cell   membrane is ruptured or lysed killing the host  cell and releasing the new generation of viruses   into the environment however as killing every cell  a virus encounters would quickly lead to the death   of the host and the viruses with it most viruses  instead exit the cell by either ectocytosis   or budding passing through the cell membrane  without rupturing it but whatever the process   the end result is the same the newly assembled  viruses are released into the environment   ready to infect new cells and start the whole  process over again now that we know what viruses   are and how they reproduce let us return to the  original question are viruses actually alive the   answer as with so much in biology depends on how  exactly one defines life unique among the sciences   there is no firm consensus within biology as to  what exactly it is that biologists actually study   while at first glance the question of  whether something is alive or not might   seem straightforward throughout history a concrete  testable definition of life has eluded even the   greatest scientific and philosophical minds with  the common consensus essentially boiling down to   well we know it when we see it but as the lack of  such a definition did not prevent biologists from   carrying on with their work for many years the  subject remained a mere philosophical curiosity   however as humanity began to explore the cosmos  and search for life on other planets the question   what is life suddenly became a much greater  priority over the years various scientists have   attempted to draw up lists of properties unique  to living organisms such as this one from the nasa   website living organisms have the ability to take  in energy from the environment and transform it   for growth and reproduction organisms tend toward  homeostasis an equilibrium of parameters that   define their internal environment living creatures  respond and their stimulation fosters a reaction   like motion recoil and in advanced forms learning  rife is reproductive as some kind of copying   is needed for evolution to take hold through a  population's mutation and natural selection to   grow and develop living creatures need foremost  to be consumers since growth includes changing   biomass creating new individuals and the shedding  of waste however many of these properties are   also exhibited by non-living systems crystals for  example can spontaneously organize into incredibly   complex and ordered shapes self-replicate and  transfer this internal order from crystal to   crystal even more in response to external stimuli  similarly a dark stone can convert solar energy   into thermal energy and then into kinetic energy  by heating the air around it while radioactive   elements can spontaneously turn nuclear energy  into thermal energy this definition even breaks   down when applied to certain biological systems  for example prions the agents responsible for   bone vines spongiform encephalopathy better known  as mad cow disease are even simpler than viruses   consisting of rogue misfolded proteins devoid  of any genetic information nonetheless prions   can mutate spread from host to host and multiply  though not by passing on genetic information but   rather by causing adjacent proteins to misfold in  a deadly chain reaction for more on this please   check out our previous video the gruesome tale of  the laughing death epidemic a more sophisticated   set of properties unique to living organisms was  set forth by austrian physicist irvin schrodinger   best known for putting hypothetical cats in  hypothetical boxes same dude in his 1944 book   what is life schrodinger remarked upon quote  an organism's astonishing gift of controlling   a stream of order on itself and thus escaping  the decay into atomic chaos in other words   living organisms appear to defy the second law  of thermodynamics which states that in a closed   system entropy variously defined as disorder or  energy which cannot be used to perform useful work   always increases in the face of natural forces  which are constantly trending towards greater   disorder organisms not only manage to maintain a  high degree of internal order and complexity but   do maintain said order over multiple generations  with very little loss of fidelity of course   organisms do not actually violate the second  law since they are not closed systems rather   they are semi-bounded systems closed off enough  from the outside world to maintain internal order   but permeable enough to allow this increase in  order to be counterbalanced by a decrease in   order outside the organism for example through  the release of waste heat nonetheless these   observations allowed schrodinger to postulate that  such a semi-bounded structure was essential to the   functioning of living organisms more importantly  he further postulated that in order to accurately   transfer their internal order and complexity to  subsequent generations organisms required some   form of code script containing instructions for  building that particular organism this prescient   prediction would of course be vindicated less than  a decade later by the discovery of the structure   and function of dna in the wake of schrodinger  scientists like british biologist john maynard   smith suggested that the fundamental property  of life was its ability to undergo darwinian   natural selection in which heritable traits  which increase in organisms reproductive   capacity are selected for and preferentially  passed on to subsequent generations allowing   species to gradually evolve over time eventually  this notion was combined with previous definitions   to produce the so-called nasa definition of life  which states that quote life is a self-sustained   chemical system capable of undergoing darwinian  evolution on the second count viruses certainly   fit the bill as the rapid mutation of covert 19  into multiple variants clearly demonstrates but   it is on the first part of the definition that  the argument for viruses being alive stumbles   for unlike other organisms viruses are unable to  replicate in the absence of other living cells   without a host cell's molecular machinery to  hijack a virus is just an inner bit of protein   and genetic material thus according to gerald  joyce of the salk institute quote according to the   working definition a virus doesn't make the cut  but for not being alive viruses certainly play an   outsized role in the natural environment while it  is impossible to know for sure biologists estimate   that there are some 10 to the power of 31 viruses  in the world as a number so mind-bogglingly large   that if laid end and these viruses would stretch  some 200 million light years well past some of   the farthest known galaxies viruses are found in  every environment on earth and in fact every known   organism though the vast majority are benign and  do not cause harmful illnesses nonetheless they   have a tremendous impact on the evolution of  life on earth particularly via the reverse   transcription of viral genes into the host's dna  for example blood oranges exist thanks to a viral   gene called tcs2 which in response to cold weather  switches on a gene called ruby that gives the   fruit its distinctive deep red hue closer to him  an ancient viral gene called ervw is responsible   for the development of a fused cell structure in  the human placenta called a syn site eotrophoblast   wow which is vital for the transfer of nutrients  to the developing embryo thus all of us so are   very existent to a virus that infected an  african mape millions of years ago for this   and other reasons certain scientists believe  the nasa definition of life is overly narrow   and should be expanded to include borderline cases  like viruses among these is french microbiologist   patrick forter of the pasteur institute who  argues that quote life and living processes   are simply names for complex evolving forms of  matter that are now present on our planet forte   conceives of viruses not simply as assemblies of  protein and nucleic acids but as organisms with   two distinct phases in their life cycles the  inert virion or virus particle and the virus cell   the living cell which has been taken over by the  virion and converted to producing more variants   in forte's model the virus cell is contrasted with  the ribosome the regular healthy form of the host   cell the difference between the two being whereas  the dream of a normal cell is to produce two cells   the dream of a viral cell is to produce a hundred  or more viral cells thus according to forte the   virine is to the viral cell what a seed is to  an oak tree and viruses are no different from   any other parasite that depends upon its  host to grow and reproduce they are simply   more dependent than most other scientists argue  that any attempt to rigorously define life is   inherently unproductive as it might prevent  us from recognizing as yet undiscovered exotic   forms of life on earth or other planets as carol  cleland a philosopher of science at the university   of colorado explains definitions tell us about  the meanings of words in our language as opposed   to telling us about the nature of the world in  the case of life scientists are interested in the   nature of life they are not interested in what  the word life happens to mean in our language   what we really need to focus on is coming up with  an adequately general theory of living systems as   opposed to a definition of life despite its  amazing morphological diversity terrestrial   life represents only a single case the key to  formulating a general theory of living systems   is to explore alternative possibilities for life  i'm interested in formulating a strategy for   searching for extraterrestrial life that allows  one to push the boundaries of our earth-centric   concepts of life on the other hand i don't think  that defining life is a very useful activity for   scientists to pursue since it is not going to  tell us what we really want to know which is   what is life a scientific theory of life will be  able to answer these questions in a satisfying way   and do the same for fringe cases merely defining  life in such a way that it incorporates one's   favorite non-traditional living entity does not  at all advance this project and so the debate   rages on with nearly every biologist being firmly  convinced that the matter has already been settled   in one way or another all we can say for sure is  that given their impact on the past the present   and the future of life on earth alive or not  viruses deserve nothing but our utmost admiration   and respect so i really hope you found  today's video interesting if you did   please do hit that thumbs up button below don't  forget to subscribe and thank you for watching

Channel: Today I Found Out

Views: 117,430

Keywords: today i found out, tifovidz12, tifo, awesome, facts, didn't know

Id: g6_ZWr0NRBA

Length: 23min 6sec (1386 seconds)

Published: Mon Feb 28 2022