My Blog List

Tuesday, January 11, 2011

cellular angst

This is my first blog in this series.  This blog is primarily intended for my cell biology and microbiology students at The Master's College.  My background is in cellular immunology/microbiology and I have been teaching at the undergraduate level for 20 years.  However I am by no means an expert in this field....there is just too much to know and a lot of things yet to discover about these smallest pieces of life.

I intend on blogging at least once a week to share insights from our classroom lectures and discussions. 

Please feel free to contact me at jfrancis@masters.edu.

So what are cells and what is the advantage to having every living thing made of cells?  How do we define what a cell is anyway?  The traditional way to define them is to distinguish them from viruses.  Viruses are typically smaller than cells and do not have a lot of things which cells have.   Recently some very large viruses with membranes and cellular biochemistry have been discovered.  One of these is the Mimi virus... a pretty big virus. It is bigger than some bacteria.  It has metablic pathways to make amino acids and nucleotides.  So is this is virus or a cell? http://www.microbiologybytes.com/virology/Mimivirus.html



Then there is the issue of unicellular life.  I have a sneaky suspicion that unicellular life does not really exist.  Curiosity peaked.  Stay tuned.

Students please feel free to answer my questions with a reply.

41 comments:

  1. Woah! This mimivirus contains 911 coding genes...that's insane! God sure is amazing! :)

    ReplyDelete
  2. ^^oh and great first blog Prof. Francis!

    ReplyDelete
  3. Bethany, Thanks for being first. Whose next!

    ReplyDelete
  4. I would still say it's a virus because it is cannot survive or reproduce independently. It's amazing how much there is out there that we don't know or understand, like how would something like the mimivirus or unicellular organisms behave the way they do.

    ReplyDelete
  5. In my opinion, it must be considered a virus, because it can only "perform most (but not quite all) of the functions of living cells." If it cannot perform all of the functions of a living cell, then it cannot be a living cell.

    However, if the definition of living cell were to be broadened even slightly, then this virus would most likely make the "live" club.

    ReplyDelete
  6. Sam and Hannah,

    Good thinking. However if we use the "independent life" criteria to help us define cells, we could probably find a number of cell types in the human body which require other cells to survive. Are these entities considered non-cells by this criteria.

    ReplyDelete
  7. After all of the searching I have done about this mimivirus, I have just been flooded with so many other questions. It is amazing that God has made even these little microscopic cells (living and non living) so unique and different from each other. At every level of life, there is so much diversity, so much creativity which points us to a Creator!

    Concerning the mimivirus though, I know that there is no "right" answer but I will play the devil's advocate and say that the mimivirus should be considered a living cell. The mimivirus has qualities such as "genes coding for nucleotide and amino acid synthesis," that even some living bacteria lack. A human who cannot feed himself on his own or cannot reproduce is still considered a human even though it does not have those two functions. Same here. Just because the mimivirus is dependent on other cells for protein synthesis and energy metabolism and it replicates like all other viruses should not disqualify it from being a "living" bacteria.

    ReplyDelete
  8. Just when we think we have defined the limits of things, we find something that is totally unique and individual and breaks some of our set up limitations. God truly is wise and ingenious with HIs creation. It just shows us that however hard we try to limit and categorize things, we see how immense and never ending God's wisdom and creativity is

    ReplyDelete
  9. To answer your question from earlier Dr. Francis, it seems like we would be forced to consider some cells in the human body to be non-cells if we stick to "independent life" as a factor for being considered "alive."

    However, I like what Sean said about how we do not consider sterile or paralyzed people to not be "alive." There is almost a sense here that scientists have more than one definition of life at work: one that applies to organisms at the cellular level, and one that applies to organisms at the macro level.

    ReplyDelete
  10. I personally believe that the MimiVirus is a virus, based on how it reproduces. It does seem like a very general answer, but if you think about it, reproduction is a big factor in classifying one organism from another (just as how you can distinguish a plant from an animal based on how they reproduce [aside from the obvious appearance of course]). Since the MimiVirus reproduces through "self-assembly of preformed components," in my opinion, I believe it is a virus.

    ReplyDelete
  11. In my opinion, the MimiVirus should be placed in the virus category. When an organism is dependent on a host cell like the MimiVirus is, it functions like any other virus. From the link that is posted on this page, there is a pivotal quote that points to the fact that the MimiVirus is still only a virus: “It does however, lack genes for ribosomal proteins, making mimivirus dependent on a host cell for protein synthesis and energy metabolism.” In my opinion, the MimiVirus is still a virus.

    ReplyDelete
  12. vi·rus

    –noun, plural -rus·es.
    1.
    an ultramicroscopic (20 to 300 nm in diameter), metabolically inert, infectious agent that replicates only within the cells of living hosts, mainly bacteria, plants, and animals: composed of an RNA or DNA core, a protein coat, and, in more complex types, a surrounding envelope.

    From a strict dictionary definition standpoint, (I realize this isn't exhaustive, but still helpful) it seems that the MimiVirus meets all of these standards. It reproduces only with the help of another cellular host (not to be compared with a reproductive parasite, as those are multicellular, as are the hosts). It also cannot synthesize its own metabolic energy due to a lack of ribosomes to create the necessary proteins.(which also differs from parasites) Since we classify viruses as non-living, and these are a virus, it makes sense to classify them as non-living. Like Sam said, I think the biggest difference between the classification of viruses and parasites (or sterile paralytic humans) is their size.

    ReplyDelete
  13. Something that caught my attention was when the article said "...as well as raising questions about their evolution." I'm now wondering, that if an evolutionist would argue that this is a living organism, despite its similarity to already classified as non-living viruses, they could then say it makes a gap between non-living compounds and life? Just a thought.

    ReplyDelete
  14. The thing about using the analogy of a dependent is that it is a disfunction if a human cannot feed themselves and not the picture of your average human. that's like saying if one human loses his or her arms, thus becoming dependent that disqualifies that human. you're talking about an individual within a species, if the MimiVirus is living organism than we're talking about an entire species here.

    I agree with Sam, if the MimiVirus, as a whole, does not perform the functions that qualify a cell and it functions like a virus than it should be considered a virus.

    ReplyDelete
  15. This is so fascinating! I'm not sure whether to classify it as a living cell or a virus, but I suppose I'd lean toward the virus arguement as well...the mimivirus lacks serious vital components for self-sustained life. however, I loved reading the article about the complexity and high-functioning abilities of this virus, and its sheer size relative to other viruses. I aboslutely love how God creates complex and unique miniscule things just to glorify himself and prove his dominion. I love being able to read about something as small and seemingly minute thing as this and be able to praise the awesome creator as a result...

    ReplyDelete
  16. Oh, and in regards to the evolution comment, I thought the same thing eric did, I'm surprised they didn't try to use it as yet another of their "missing links"...

    ReplyDelete
  17. I don't understand how God thinks of this kinda stuff.
    I would classify this as a virus because it acts just like other viruses in the fact that it relies on a live host, and is dependant on other cells.
    I still don't understand how God creates these things. I know He is omniscience but still, incredible!

    ReplyDelete
  18. WOW Dr. Francis, this blog idea is just swell, I love it!! It amazes me how technologically advanced we are in the classrooms nowadays...
    So to be special and kind of unoriginal, I am going to comment on the MimiVirus. I found it interesting how they have found the virus in pneumonia patients...I want to know how this gigantic virus effects the system, if it does at all. What is its purpose since it said it is similar to another disease causing virus?

    -Sarah Gonzales

    ReplyDelete
  19. Hmmm. I would say that the Mimi virus sounds more like a virus than a virus than a cell, for various reasons. Also, since whoever decided to name this virus called it a virus knows more about it than me, so I am sure that they had a good reason for calling it a virus and not a bacteria! Interesting thought either way!

    ReplyDelete
  20. It seems to reproduce like a virus....

    ReplyDelete
  21. I think Mini would be a virus since it does not have genes for ribosomal proteins, lack of ability to metabolize, and reproduces through replication, which is different from the living cells.

    ReplyDelete
  22. Based on the definition we have today I would consider it a virus. But there is so much about the cellular world we just don't know about yet. The mimvirus could just be one of millions of types of these cells. This could just be the discovery of a new group of cells that neither fit in the bacteria or virus classification. We have so much more to learn and discover in this area of study that it is hard to have a hard and fast classification for anything.

    ReplyDelete
  23. I believe that it is a virus, as it cannot live independently. It also shares many of the traits as a virus, such as its method of reproduction. Just because it contains DNA that some bacteria do not have does not mean that it is more similar to a bacteria than a virus. Consequently, it cannot be alive.

    ReplyDelete
  24. Ok all these comparisons to human cells has got me wondering if maybe scientists should define "living" differently than whether or not the cell can survive "on it's own." Obviously if some epithelial cells get scraped off a person, then those cells die. If you remove all the nervous cells from a person then everything else in the body dies. If you kill all but one samonella bacteria, that last bacteria won't necessarily die as a result. A macro-organism human can survive with its own cells. A micro-organism like samonella can survive with its own cell. A mimivirus can not survive with just itself. As long as we don't count on "feeding" on other cells as a dependancy on them for life (which it kinda is) then this all works fine.

    ReplyDelete
  25. I agree with Micayla in that whoever named the mimivirus obviously believed it to be a virus, and normally those people that go around naming things normally know what they are talking about... just a thought.

    to expand on what Kaitlyn Preheim said, there is so much that we still don't know about cells and viruses. It contradicts my previous point, but just because the human race has given something a specified term doesn't make it a flawless. When things are named, it is often when they are first discovered and knowledge is minimal.

    I definitely agree with Jordan. Even rbcs or epithelial cells, like Jordan mentioned, die when they are separated from others.

    ReplyDelete
  26. Its important to remember classification is not a absolute science, it is based on what we already know in nature and how other things fit in with what we know. The mimivirus looks and acts like a virus, although it is more complex and bigger than most other viruses. Based upon what we know now, it would not fit into the classification of "cell."

    ReplyDelete
  27. I would the call MimiVirus a virus due to the fact that lives within a living host and it does not have any vital organs so it kinda of fit into the virus class if you ask me

    ReplyDelete
  28. A cell is a membrane bound physical entity that has genetic material which participates in its self-replication. Cells can interact with other cells forming tissues which are the base for macro organismal life. Some cells are more independent than others and do not require macro organismal life for survival. Some advantages of having everything made of cells are this multicelled state leads to specialization, modularity; they can modulate between different functions, and protection; if one cell is compromised the whole organism does not die. Even though the mimi virus is pretty amazing I still don’t believe it has all the qualities that encompass a cell. For one thing, the mimi virus could never form a tissue. Even though not all cells do this the mimi virus is also completely dependent on a host for survival.

    ReplyDelete
  29. I would say that the Mimivirus is a virus for a few reasons. Although it does have some capabilities of a cell it lacks major areas that are vital for a cellular definition. The fact that this virus cannot create it's own proteins I would say is a major factor for calling this a virus. It's division and reliability on a host cell restricts it of major cell functions.
    I would say that their is unicellular life. Although cells rely on other organisms, all organisms rely on other organisms to survive so this dependency is not new. Accordingly I would say that unicellular life exists.

    ReplyDelete
  30. The Mimi virus is dependent on a host cell and shows to function like other viruses. It also lacks ribosomal proteins, which makes it dependent on the host cell genome for protein translation and energy metabolism.
    These factors cause the debate on whether or not the Mimi virus is a distinct form of life.
    I think that becuase it lacks such vital components for life, it would be classified as a virus.

    ReplyDelete
  31. Cells are small living entities which make up living organisms and are made up of a variety of different components(a couple of which are the same between prokaryote and eukaryotes like DNA). This cell also will have some sort of membrance to keep its components inside. This is definitely a lacking definition but it was all I could come up with on the spot.
    Wow the Mimivirus is huge! I can't believe that a virus could be that large and have so many genes coding for it in such a small, by comparison to cells yet large as viruses go, virus. I think it is stil a virus because it has all the characteristics of a virus, just it is a super large virus obviously.

    ReplyDelete
  32. How do we define what a cell is anyway?
    1. The structural, functional and biological unit of all organisms.

    2. An autonomous self-replicating unit that may exist as functional independent unit of life (as in the case of unicellular organism), or as sub-unit in a multicellular organism (such as in plants and animals) that is specialized into carrying out particular functions towards the cause of the organism as a whole.

    3. A membrane bound structure containing biomolecules, such as nucleic acids, proteins, and polysaccharides.


    Supplement

    There are two distinct types of cells: prokaryotic cells (e.g. bacterial cells) and eukaryotic cells (e.g. plant or animal cell). The main difference between the two is a well-defined nucleus surrounded by a membranous nuclear envelope present only in eukaryotic cells. Despite this difference they share a number of common features: the genetic information is stored in genes, proteins serve as their main structural material, ribosomes are used to synthesize proteins, adenosine triphosphate is the main source of metabolic energy to sustain various cellular processes, and a cell membrane that controls the flow of substances into and out of the cell.
    http://www.biology-online.org/dictionary/Cell

    ReplyDelete
  33. Cell Definition:
    By definition a cell is a very small unit of living matter that makes up organisms and is made up of specific organelles that carry out functions vital to life of the cell and life of organisms. A way many scientists have defined cells is by certain ccategories, basically whether they contain a nucleus or not. Therefore you have either a prokaryotic cell or a eukaryotic cell.

    Mimi Virus:
    According to wikepeida the classification of mimivirus as a pathogen is tenuous at present as there have been only a couple of papers published potentially linking mimivirus to actual cases of pneumonia. One could say this is a virus over a cell because they lack genes for ribosomal proteins, making mimivirus dependent on a host cell for protein translation and energy metabolism. They also do not exhibit the following characteristics, all of which are part of many conventional definitions of life: homeostasis, response to stimuli, growth in the normal sense of the term (instead replicating via self-assembly of individual components) or undergoing cellular division. I would conclude the mimivirus as a virus.

    ReplyDelete
  34. 1) Cells are pockets of disequilibrium. They can reproduce, grow, adapt, and maintain homeostasis. All cells are contained by a membrane of some sort and have a storage location for their DNA, whether that be nucleus or nucleoid. Most cells work together to form bigger living organisms.

    2)The mimivirus is a virus. it cannot reproduce on its own or do many of the functions that cells can perform. It therefore is not technically alive. Which poses evolution and interesting question: what is a nonliving entity doing carrying around DNA. Why would it need DNA? in any case, if it looks like a duck but barks like a dog, it is most likely a dog wearing a duck costume. or a duck with a bad case of laryngitis.

    ReplyDelete
  35. I would say that the mimivirus is a virus because it a host of a protein. Cells aren't host of anything at least that's what I thought. Cells don't rely on other organisms the way viruses do.

    ReplyDelete
  36. The cell is the most basic units of life. There are millions of different types of cells such as brain cells, skin cells, liver cells; all of which have unique functions and features. Although cells have similarities, there are also major differences. Some cells are unicellular like bacteria, and some cells are multicellular like humans. There are two types of cells: eukaryotic and prokaryotic. The eukaryotic cells are usually found in multicellular organisms.
    After reading about the mimivirus, I would say that it is a virus because according to the linked article on mimivirus, it states that mimivirus “lack genes for ribosomal proteins, making mimivirus dependent on a host cell for protein synthesis and energy metabolism”.

    ReplyDelete
  37. mimivirus seems to have made quite and impact on many scientist with its unusualness. well like all viruses this particular also doesnt have a cell wall, and according to everyone else on here its a virus so im leading towards the fact that its a virus.

    ReplyDelete
  38. Wow there have been quite a few comments on this blog. So after doing quite a bit of research on this virus/cell/bacteria I think that biologists simply need to redefine what a cell and what a virus is, because obviously, as everybody has stated, there are reasons to call the mimivirus a cell and a reason to call it a virus. A cell has a nucleus, genetic material, and has some sort of membrane on the outside. Since there are arguments for both sides, once the definition of a cell or virus has been defined further, then we can all agree on the same thing:)

    ReplyDelete
  39. This comment has been removed by the author.

    ReplyDelete
  40. These mimivirus to be are still a virus, the name itself is obvious. Its just like regular coffee and decaf coffee, both a still coffee one just lacks caffeine. Another reason why I would consider them to be viruses is that they seem to have to rely on something, its as if a host is needed.

    ReplyDelete