I was discussing with Philo (in the vampire writing challenge) whether Red Blood Cells (erythrocytes) are alive or dead and it got me interested in fellow Hatrackers' gut call (or any other call) to answer that question.
The Poll question: Are Red blood Cells alive? Yes? No? Maybe? Can you give your reasoning or belief?
Clinically, they are not considered alive. they are essentially nature's selfreplicating 'bots.
viruses are DNA or RNA in a protein capsule that can enter a specific host cell and uses the cell's machinery to selfreplicate. Their exactly like a computer virus - a piece of selfreplicating material.
But it all depends on what definition you want to use.
Some keep it loose - any "ability to replicate". Some narrow the definition a bit - "ability to self-replicate"; some add "reacts or adapts to environment"; some add more "can maintain an internal environment" (homeostasis), etc.
look up life in wikipedia and they have 7 or 8 guidelines that biologists use to define life. By those guidelines a virus is not alive.
One interesting definition is living things "extract energy from it's environment." (which goes hand-in-hand with the energy needed to maintain homeostatis). Viruses don't do this.
[This message has been edited by billawaboy (edited March 19, 2010).]
RBC's are alive in the exact way that a terminally differentiated white blood cell, like a lymphocyte, is alive. It is a terminally differentiated cell in a complex organism...this cell has lost some of what it was 'born' with.
So, if you define a WBC cell as alive, then so is a RBC. However, WBC cell cannot create more WBCs only the stem cells in the marrow can do that, this is also true of RBCs. Usually, a cell the undergoes terminal differentiation loses the ability to reproduce, but I may be behind on my literature on this one. the field of stem cell biology is crazy right now and thank god for that!
When you compare life, it's not a fair comparison to talk about RBCs and viruses. An RBC is a component of a living organism. Is a mitochondria alive? I would not hazard a guess now, but it likely was at some point. Now a virus, that's one for the philosophers but it seems pretty clear that the definition of life is on a sliding scale.
[This message has been edited by LAJD (edited March 19, 2010).]
When dealing with RBCs and vampires, you are extracting them from their native system. So, in determining if they are alive for the vampires, you need to consider them outside of the system (as the vampires would be considering them). If you take say fibroblast cells out of the system and give them food, they replicate like crazy, which RBCs don't do. So, taken outside the system, it looks like they are dead.
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LAJD - differntiated yes, but RBCs are anucleated - no DNA! - and no organelles, especially mitochondria. WBCs still have all of thiers. That's a big difference between living cells and dead cells.
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Yes, RBCs in mammalian cells are anucleated. But they most definitely have nuclei in birds and reptiles, yet do not replicate and perform the same function.
To your point "Normal cells- eat, grow, adapt, replicate" Well, no. actually they do not. They definitely eat and grow and some can adapt but not all- many terminally differentiated cells just die in a new envrionment. Many cannot replicate- as I said above. Are those dead? No they are part of an organism.
You are comparing apples and apple orchards. Leslie
Actually, even terminally differentiated cells adapt - that's the whole science behind pathology of blood cells - how they adapt to environmental stimuli.
I think we maybe be thinking of different meanings of 'adapt.' I'm thinking adapt as used in the science of pathology - typically adaptation to cellular injury caused by noxious stimuli. Anucleated (i.e. dead) cells don't adapt.
Edit: Also differentiated cells can replicate - T-cell and B-cell proliferation to cytokines are one example.
Note that differentiated cells aren't permanently that way - they still have the original genome - it's just turned off. With the right nuclear signals you can turn them back on. It all depends on the stimuli. Also note there is a thing called dedifferentiation (not in humans though...)
So I still stand by eat, grow, adapt, replicate - even for differentiated cells. it all depends on the stimuli. Any cell can die in a noxious enough environment. Some cells are more sensitive. But they are alive.
Mature human (I had though human was implied, but i'll be explicit) RBCs don't adapt at all to noxious stimuli. They just get destroyed. In fact they don't eat, or grow, or adapt, or replicate.
It's cause they're dead.
[This message has been edited by billawaboy (edited March 20, 2010).]
Billawaboy, I will continue our conversation here - therefore I will post what I emailed you today:
I looked at the requirements you listed for a cell to be considered "alive". If all of these are required, then we might as well say thay we are all brain dead after about 25 years of age, which you may think about me at this moment. Brain cells (neurons) do not have many of the qualities that are listed here - such as homeostasis (since they do not exist independently), growth, adaptation (very limited, especially after age 25), or reproduction. I would suspect there are a variety of cells (other than RBCs) within living animals that also lack many of these qualitiies. These requirements would seem more appropriate for independent living organisms.
What appears to me to be the problem is the difference between the terms "alive" or "living" and the term "life" (not the insurance kind).
I will look into what you are stating some more, but I do not believe that RBCs would be considered dead, especially since they appear to actually go through a dying process after about 120 days. I could possibly be comfortable stating that they are organic vehicles, but normal RBCs do not meet my definition of death, which involves the collapse of cellular integrity.
i need to give you an example of homeostasis. The fact that a cell maintains an internal membrane potential of -60mV and a pH of ~7 means that neurons are homeostatic. They have to maintain an internal cellular environment - thats what homeostasis means: "keep same state" The fact that neurons transmit signals and return to it's original state is also homeostatis in action. When glucose is low, neurons express proteins to get energy from ketone bodies (this happens during starvation) - that's adaptation to maintain homeostatis! See?
Neurons do go thru all the guidelines of life - they grow and adapt - neural plasticity is an example nicely covers all those. the only thing it doesn't do on it's own is replicate -- but with the right signals it can be pushed from G0 state to G1 - but that is considered a pathology of neurons. Dead cells dont respond to signals. All the rules of life are there for every cell- it's just the proper signals keep everything in check.
RBCs don't 'die' - it's just bad phrasing - they just get damaged or oxidized. There's nothing there to die. After 120 days the cell membrane rips and hemoglobin spills out. It's just wear and tear on a bag of hemoglobin.
Yes I was thinking of evolutionary adaption and you were thinking environmental, but they do cross. And you do realize that this is like debating the length of a string, right? LOL.
You are correct on that blood cells do adapt, in a sense, in those cases. B & T Cell Proliferation is a very specialized kind of terminal differentiation and also requires marrow and stem-like progenitor cells. The cytokines trip the process to create specialized pools of differentiated B/T cells. Once those specialized cells are created they cannot go back to being non-specialized. There are also cells in the brain and gut that are actually a better example for your argument because they do not require a progenitor pool and probably other places that I do not know about. 8-)
And as you note dedifferentiation is not in humans and only very recently found in a planaria-like thing (I cannot recall what it was..). Also not all differentiated cells contain the full genome, many do not. There were a number of chimera studies in the early 90s that showed that during development in certain tissues genes were not just turned off during embryonic development but genetic material was lost. Those were in mice, mommies frown on freezing and slicing up little bobby.
However, I think my argument of blood cells as a part of a living organism and therefore the apples and apple orchards argument is the most reasonable.
Is a mitchondria alive? A nucleus? A panceas? Testes? (still reading?) All of those are living tissues. Blood is living tissue and RBCs are a component of living tissue. I don't think that the argument stands up because you are talking about something that is an integral part of a living tissue. It is complex and cannot be sustained outside of the body. Can you keep a glass full of blood alive or active or whatever, without some preservative outside of the body? No, you need something to keep it liquid and slow down the reactions. You cannot do that with compacted RBCs either, they turn into a mass of useless goo, even if you clean away everything else. It's because there are complex biochemical reactions (ATP is definitely--> ADP in a mature RBC), they have lysosomes and lytic reactions and are chowing through glucose in a manner that we call life for whatever is going on inside them. So if you want to keep them to play with outside the body you have to slow them down. They are definitely jumping around - at least biochemically.
Mature RBCs are sufficiently complex and integral part of a tissue to be considered alive.
Okay. I think we are getting very loose with the definition of alive here.
First I don't see the connection between Differentiation and the criteria for life. Second, just calling a tissue 'living' doesn't make it so. Is it the serum - the platelets, the proteins, the lipids, the sugars, etc - that's 'living'? Or did you mean the cells in blood tissue are 'living'? Just makin' a point...
But moving on...I'm getting the idea that you're trying to say using terms like 'alive' or 'dead' is moot since it's all biochemistry anyway.
But then why even call *any* cell alive at all? - just call the entire human body dead or inanimate since it's all molecular interactions anyway. We can say it's all bio-machinery - it's all inanimate stuff reacting to it's environment on a massive scale.
...Or is there a specific criteria beyond the sum interaction of biomoleclues that is defined as 'living'? I think you can agree there is. Then what is that criteria for living cells? - and do RBCs have it?
I'd wager they don't.
To me, homeostasis is the topmost necessary (but not sufficient) criteria for life - and RBCs don't even have that.
Mitochondria and gametes are definitely on the fence since they fit most of the criteria for life.
On those two I could swing either way and it would probably require refining the criteria to come to a definite conclusion.
It is really a matter of function. Like many other types of cells, they are made to perform a function. like hair, skin or fingernails.
Tree branches and bark are not alive. Plants only grow from certain regions within the plant (Meristems) the epidermal regions of humans are the same, our skin does not develop on the surface cells are produced, cease to function, and shed.
there are many cells within us that do not reproduce, just created.
Life (and death) are terms that originated long before the knowledge of cells, so there is a strong argument that they can only apply to entire organisms, and not to the components of those organisms - for cell activity we appear to need a whole set of different classifications than simply "alive/not alive". After all, some cells can carry on "living" after the death of the organism of which they are part, whlie other cells are "dead" yet remain an integral and structural part of a living organism.
It's rather like looking at one component of a clock and asking whether it is running or not. It might be working (e.g. pendulum swinging) but the clock hands might not be turning because of a failure elsehwere in the mechanism; or it might be a completely inert part (e.g. the face) of a working clock.
I'm with LAJD, she makes many excellent points.
Here is my take.
A. Red blood cells are cells whether they have a nucleas or not.
B. There is a big difference between a functional (live) RBC and a nonfunctional (dead) RBC.
c. Really the whole live or dead applies to the organism as a whole and not the parts of the organism. A cell is made of of proteins, DNA, lipids, carbohydrates, etc. All of these are dead by themselves but together they make a cell and are all crucial components to making the cell alive. Same with multicellular organisms. If you remove the blood from the person, the person is dead. It is a component that is essential for making the organism as a whole alive.
In a simplified version: Can a red blood cell live outside the human body? no.
When it no longer functions does it change? yes.
Therefore I agree with the person above who characterizes the blood cell as functioning or not functioning.
I don't think a heart is 'alive'. I think of it as operating. I certainly think of it as being comprised of living tissue and I think of blood as a living component of my body (as opposed to hair and nails.) because it is functioning, but I think alive indicates the means to exist independently.