Mitochondria and Alien life

[Neverfly]

Someone mentioned mitochondria in another thread.
I recall what I learned in high school about mitochondria, but did a quick brush up on Wikipedia.
http://en.wikipedia.org/wiki/Mitochondrion

Mitochondria are considered to be related to aging and death.
They are also symbiotic organisms, not originally part of cell structure but tagged in at some point, leading to (essentially) a big part of life as we know it.

It really got me thinking about how unique this feature is.
And wondering: What would life on another world develop into if they had a very different process of cell biology?

Is it possible that they would experience death and aging very differently?

A pure speculation topic, I know.

[Joe Boy]

Someone mentioned mitochondria in another thread.
I recall what I learned in high school about mitochondria, but did a quick brush up on Wikipedia.
http://en.wikipedia.org/wiki/Mitochondrion

Mitochondria are considered to be related to aging and death.
They are also symbiotic organisms, not originally part of cell structure but tagged in at some point, leading to (essentially) a big part of life as we know it.

It really got me thinking about how unique this feature is.
And wondering: What would life on another world develop into if they had a very different process of cell biology?

Is it possible that they would experience death and aging very differently?

A pure speculation topic, I know.

It shouldn't be all that hard to research--as you know there are aliens living among us right now . . .

[Neverfly]

It shouldn't be all that hard to research--as you know there are aliens living among us right now . . .

Yeah, but the gub'mint silences them.

[grant hutchison]

Well, the relationship to ageing and death is because mitochondria are the site of aerobic metabolism. They do all that powerful stuff with oxygen which produces free radicals, which attack DNA (primarily mitochondrial DNA, since it's nearby) and eventually cause the shut-down of mitochondria as well as more general errors in DNA transcription. Or so the "free radical" theory of ageing goes.
Maybe alien cells could keep their oxidative metabolism and their DNA (or its equivalent) better separated, if they didn't do the eukaryote trick of importing another DNA-based organism to do the aerobic work.

Grant Hutchison

[Joe Boy]

Well, the relationship to ageing and death is because mitochondria are the site of aerobic metabolism. They do all that powerful stuff with oxygen which produces free radicals, which attack DNA (primarily mitochondrial DNA, since it's nearby) and eventually cause the shut-down of mitochondria as well as more general errors in DNA transcription. Or so the "free radical" theory of ageing goes.
Maybe alien cells could keep their oxidative metabolism and their DNA (or its equivalent) better separated, if they didn't do the eukaryote trick of importing another DNA-based organism to do the aerobic work.

Grant Hutchison

See how easy that was Nev, Grant just beat me to it, alas . . .

[Neverfly]

Well, the relationship to ageing and death is because mitochondria are the site of aerobic metabolism. They do all that powerful stuff with oxygen which produces free radicals, which attack DNA (primarily mitochondrial DNA, since it's nearby) and eventually cause the shut-down of mitochondria as well as more general errors in DNA transcription. Or so the "free radical" theory of ageing goes.
Maybe alien cells could keep their oxidative metabolism and their DNA (or its equivalent) better separated, if they didn't do the eukaryote trick of importing another DNA-based organism to do the aerobic work.

Grant Hutchison

I was under the impression that mitochondrial DNA lives in the nucleus with the cells DNA. Roommates.

[grant hutchison]

I was under the impression that mitochondrial DNA lives in the nucleus with the cells DNA. Roommates.

No, it lives in the mitochondria, which is why it's first in line to take the free-radical hit. (IIRC, mitochondria don't have the same DNA repair mechanisms as the nuclei, either.)

This is why mitochondrial DNA (largely) traces the female lineage. The egg cell carries its own mitochondria, which of course come from the mother. The sperm cell (usually) leaves its mitochondria outside the egg along with the sperm tail, while the sperm head enters the egg. So the fertilized egg contains paternal and maternal nuclear DNA, but (usually) only maternal mitochondrial DNA.

Grant Hutchison

[eburacum45]

They are also symbiotic organisms, not originally part of cell structure but tagged in at some point, leading to (essentially) a big part of life as we know it.
It really got me thinking about how unique this feature is.
And wondering: What would life on another world develop into if they had a very different

Perhaps not that unique, since chloroplasts probably have a similar origin;
http://en.wikipedia.org/wiki/Chloroplast

In general, they are considered to have originated as endosymbiotic cyanobacteria (previously known as blue-green algae).

So every plant has symbiotic chloroplasts as well as symbiotic mitochondria.

[Neverfly]

Perhaps not that unique, since chloroplasts probably have a similar origin;
http://en.wikipedia.org/wiki/Chloroplast
So every plant has symbiotic chloroplasts as well as symbiotic mitochondria.

Perhaps.
But it also happened very early in the development of life on this planet.

[eburacum45]

Perhaps.
But it also happened very early in the development of life on this planet.

More than a billion years ago, but proabaly well after the emergence of life. For billions of years there may have been no chloroplasts. Maybe early lifeforms regularly assimilated each other, like microscopic Borg; we only see the ones that survive.

[aastrotech]

The "mitochodrial relationship" of cells probably formed early in the history of life as some cells were able to use the excretions (waste) of other cells as food. As cells evolved one of the cells involved in the "relationship" became "protective" of the other cell. Likely the cells were almost identical and almost certainly closly related both geneticly and environmentaly. Eventualy one cell domesticated (brought into the home, the body, of the cell). The cell became us. The mitochondria became the "powerhouse" (supplying neccesary proteins to our DNA as their waste) of our cells.

Off topic

Mitochodria mutate at a regular rate. That's how we can tell the ancestry, through the female line, of people. Some recent research on mitochondria indicates that mutations of mitochondia, over time, result in mitochondria that, over the life of a creature, lessen their contribution to the needs of cells. It is (very recently) speculated that this reduction of needed mitochondrial contribution to cells causes the aging and death of cells.

In short, the aging of cells resembles starvation of cells. Our cells are not getting their food from the too far mutated mitochondria. Recent speculation is that by either resetting the clock (or mutation state) of mitochondria or by finding other life forms with mitochondria of a "compatible" state of muation we may be able to stop aging.

In the literature there is some speculation that mitochodria get "damaged" over time. Undoubtedly they do. However damage is irrelevant to their structure as they reproduce by fission and it doesn't matter weather they are in an individual or in the reproductive path. The mutations are part of their resistance to damage over time. So far (3 billion years) that resistance has been succesfull. Thus changes in mitochondria resulting in bad results for the individual are not neccesarily "damage".

[nildor]

This discussion assumes that aerobic respiration, requiring mitochondria, would be the ideal mode of energy generation by "aliens". This also assumes that the ecosystem for alien evolution is similar to earth. If that was not the case, and the alien ecosystem had reduced carbon compounds available (much like we have oxygen) then alien cells could evolve without the need for these energy factories. For example, a high methane content on a planet with temperatures allowing liquid water might just result in life based on anaerobic respiration instead.... Although less efficient than aerobic (mitochondrial based) respiration, sufficient concentrations of methane would allow life.

[Vultur]

Perhaps.
But it also happened very early in the development of life on this planet.

It's happened multiple times. And some species have learned the trick of 'stealing' chloroplasts from others; the sea slug Elysia chlorotica has not only done this, but introduced enough algal genes into its nuclear DNA (since the chloroplast DNA is not entirely 'self-sufficient') that the chloroplasts survive for the slug's whole lifetime, and are used to photosynthesize (feeding the slug).

It's been argued that the supposed unlikeliness of the events that produced mitochondria/chloroplasts make complex life unlikely, supporting the 'rare Earth hypothesis'; but there's no reason to think endosymbiosis events are really that unlikely (given billions of years and millions of species to work with), since they've happened repeatedly on Earth.

For us to make that same journey would require generation ships, a solution that raises significant moral questions.

Perhaps a bit OT, but why? I don't see any reason why life on a generation ship would be worse than on Earth. Most human beings throughout history have lived and died within a tiny area of their birthplace.

[coreybv]

Perhaps a bit OT, but why? I don't see any reason why life on a generation ship would be worse than on Earth. Most human beings throughout history have lived and died within a tiny area of their birthplace.

Right, but at least they had the option to wander off. Here on Earth, if I decide to move from a city to a remote, small town, once my children grow up they can pack up and move right back to the city if they want to.

Someday we'll be able to build a suitable ship, but that's a long, long way off. Anything that's even remotely feasible with near term technology would be a miserable life. Cramped quarters, no fresh air, no "outside"... The people who arrived at the destination would probably have little psychological resemblance to humans back on Earth.

Down the road if we can build, say, a Babylon 5 sized ship, complete with garden areas, etc..., then it's less of a problem. But even then, it's a smaller environment, the children born there would have fewer options about what to do with their lives.

Then at the end of the journey, the people on the ship will have to be settlers on an unfamiliar world, with all the hardships that come along with that. While they're hunting dangerous animals for food, folks back home are having a pizza delivered right to their door.

I guess I just don't feel that I have a right to make that decision on behalf of all of my descendants.

I'm not saying "I'm right", or that there aren't other ways of looking at it. But that's my personal opinion on it.

[Vultur]

Right, but at least they had the option to wander off.

Not really. I mean, yes, they had the physical capability to walk off, but usually they wouldn't have survived. It's a very recent development (on the scale of human history) for people not to be dependent on a tight-knit social group for survival. Through most of human history over most of the inhabited world, strangers were enemies almost by default.

In this, as in many things, our era is very much the exception.

Someday we'll be able to build a suitable ship, but that's a long, long way off. Anything that's even remotely feasible with near term technology would be a miserable life. Cramped quarters, no fresh air, no "outside"

Consider, however, that we are becoming a more and more computer-mediated, indoor society. Most people of the generation which is currently being born will probably be more-so than anyone today. And if you were *raised* there, it would certainly not be a problem.

And how small a ship are you imagining? I'm thinking something a mile or two across, that *looks* 'outdoors' (since the life support is all done by a closed-cycle ecosystem, as on Earth). Probably heavily modified from a small asteroid, with colossal light sails (or your favored means of propulsion) added on.

Then at the end of the journey, the people on the ship will have to be settlers on an unfamiliar world, with all the hardships that come along with that. While they're hunting dangerous animals for food, folks back home are having a pizza delivered right to their door.

On the other hand, no disease that could infect them, and freedom from all the conflicts and traumas built up over thousands of years of Terran history, and a whole new planet.

I guess I just don't feel that I have a right to make that decision on behalf of all of my descendants.
.

I don't see it as being any bigger than other decisions people generally make which will affect their descendants. Every decision we make about what paths to follow in our society affects the world our descendants will inherit, often in irreversible ways. There were paths open to us 50 years ago which are now forever closed.

[grant hutchison]

Perhaps not that unique, since chloroplasts probably have a similar origin;
http://en.wikipedia.org/wiki/Chloroplast
So every plant has symbiotic chloroplasts as well as symbiotic mitochondria.

Chloroplasts are a subset of a general class of plant endosymbionts called plastids, used for photosynthesis and storage. The plastids, interestingly, also have their own internal genome, usually inherited from only one parent. (The exact inheritance pattern varies according to the reproductive method of the plant.)

Grant Hutchison

[Ara Pacis]

Interesting. I was just reading about endosymbiosis last night after being lead there by research into The Force from Star Wars (midichlorians is supposed to be a portmanteau of mitochondria and chloroplast).

What I find interesting is that mitochondria suffer damage but still continue to fission and serve our needs. I know we think of it as the cause of death in use, but in reality, that collection of chemicals represents a single lifeform that has lived continuously for billions of years. That's all but immortal. Actually, all our cells are like that, in some sense, although we don't think of it that way.

However, I don't know that endosymbiosis must occur in all life-forms. It may be possible for alien life to develop those characteristics in-house. Even if they don't develop it through direct mutation and evolution, they might obtain it using a plasmid type of genetic transfer or via viruses or viroids.

[Ara Pacis]

doublepost

[agingjb]

I see no necessary reason to suppose that examples of replicative complex carbon chemistry elsewhere (if any) have any analogues of cells, let alone mitochondria.

[centsworth_II]

I see no necessary reason to suppose that examples of replicative complex carbon chemistry elsewhere (if any) have any analogues of cells, let alone mitochondria.

Cells are simply a means of separating the machinery of life from the surrounding environment -- a border (membrane) with an inside and an outside. Are you saying that extraterrestrial life (if any) would likely be cellular, but with different machinery? Or are you saying that there is no reason to believe that such life would even be in a form that could be called cellular?

[agingjb]

I simply don't think we know enough to do more than guess. Nothing would surprise me.

So I would only guess that there could be an almost unimaginable variety of phenomena, because carbon chemistry is demonstrably complex and potentially rich, some of which might be analogous to our biosphere. But I accept that others are more positive in their speculations.

[DrWho]

I simply don't think we know enough to do more than guess. Nothing would surprise me.

So I would only guess that there could be an almost unimaginable variety of phenomena, because carbon chemistry is demonstrably complex and potentially rich

But surely that complex carbon chemistry must take place within minimally confined region for stability of operation. We call these cells, and while I can't prove it, I'd be very surprised if alien life didn't operate on a similar principle. Cell like structures and/or lipid membranes do form spontaneously in nature and would seem to be ideal places to set up a chemistry lab.

[Disinfo Agent]

It surprises me to see mitochondria referred to as symbiotic organisms. I thought the standard term was organelles. Maybe it's changed.

Endosymbiotic theory

"Life did not take over the globe by combat, but by networking" Lynn Margulis and Dorion Sagan.

[agingjb]

It may be that analogues of cells are "common" ; but I wonder if our single example is enough to do more than guess at rules for the rest of the universe - the chemistry yes, the structures perhaps not.

[eburacum45]

Another possible scenario is that the various plastids and mitochondria-analogues that come together to make an alien cell form a colonial organism rather than become endosymbiotes. A slime-like mass filled with freely moving semi-independent organelles, which extrude the mass for protection and external storage of nutients could evolve into a complex volvox-like structure with specialised parts, an internal skeleton and transport system, but no permanent internal cell walls. The problem with an organism with no cell walls it that it could suffer extreme fluid loss if it is punctured in any way. Basically a macroscale single-celled organism. The largest ones on Earth include the 3cm Gromia. Could they grow to whale-size on other worlds?

Multicellular organisms do stand a better chance of survival if they suffer trauma, as they have many smaller, self-contained units to retain fluid (but animals, at least, run the risk of death by bleeding circulatory fluid, something which is not such a threat to plants). If macroscale single cells are possible, they would need some system of rapid response to trauma to prevent excessive fluid loss.

[centsworth_II]

Another possible scenario is that the various plastids and mitochondria-analogues that come together to make an alien cell form a colonial organism rather than become endosymbiotes....

As Disinfo Agent said a few posts back, "It surprises me to see mitochondria referred to as symbiotic organisms. I thought the standard term was organelles."

Mitochondria may have begun as endosymbiants a couple of billion years ago, but it is wrong to refer to them as such now.

What you describe seems more like a giant cell with many organelles rather than a colonial organism which would be formed of many individual cells. The colonial organism would not suffer the leakage of contents problem you describe, the giant cell would.

[centsworth_II]

It may be that analogues of cells are "common" ; but I wonder if our single example is enough to do more than guess at rules for the rest of the universe - the chemistry yes, the structures perhaps not.

I don't understand your point. The chemistry is the rules. As far as structure goes, there are a myriad of cell types represented in Earth life.

There are even so many body types represented on Earth that, if the chemistry is the same, it's hard to imagine an extraterrestrial life form that won't resemble some Earth organism.

[eburacum45]

An interesting piece in New Scientist about one possible location for the first emergence of life; the extreme chemical gradients around an alkaline thermal vent. The conditions for certain organic chemical processes are so favourable here that , according to Bill Martin and Mike Russell, bubble-like temporary protocells might have formed and dissolved in the vent enviroment. Only when permanent cells with self-sustaining metabolisms are formed can life move away from these vents; an event which may have happened twice, once to form the Archaea, once to form the Eubacteria.
http://rstb.royalsocietypublishing.o...nt/358/1429/59

If so, we might find some, or many worlds up there where life is still obliged to remain in close contact with thermal vents- and which only forms cells on a temporary basis.

[coreybv]

Is it possible that they would experience death and aging very differently?

A pure speculation topic, I know.

Even further into speculation, but this also brings up the logical follow up question (which I am by no means the first to ask):

Would a species where individuals have a lifespan of 100,000 years view interstellar travel as being as impractical as we do? (But that's probably an entirely separate discussion in its own right.)

[Nick Theodorakis]

Even further into speculation, but this also brings up the logical follow up question (which I am by no means the first to ask):

Would a species where individuals have a lifespan of 100,000 years view interstellar travel as being as impractical as we do? (But that's probably an entirely separate discussion in its own right.)

Perhaps having such a long lifespan might make one much more risk-averse than we are. For example, I would guess that if your natural lifespan was 100,000 years, you would probably give up traveling by car, since you would have a high probability of dying in a car accident before old age claimed you. Similar reasoning might forestall space travel.

Nick