Creatures similar to life, but not quite the same as our own?

[JonM]

I don’t know much about genetics so forgive me if this question is futile,

 

But lets imagine for an moment that on some distant planet somewhere, hydrocarbons (or hey why not other types of molecules) formed something similar to DNA and RNA, but not quite the same, but still being able generate something similar to life, just not life as we see it. Maybe their DNA is not a double helix and uses some other form to hold its genetic information? Maybe life can be made out of non-carbon based molecules? Perhaps that 'life' would have unimaginable characteristics…

 

Sorry if this question is stupid, I just thought to myself why is it only DNA and RNA as we know it that is responsible for life?

[ecoli]

What exactly is the question you're trying to ask?

 

And yes, it is possible that alien life could've have some sort of hereditary code in a molecule much like our own DNA.

[bascule]

Sorry if this question is stupid, I just thought to myself why is it only DNA and RNA as we know it that is responsible for life?

 

It's because all life on Earth is really just one enormous chemical chain reaction, so we all share heredity with the progenotes, which likely started as entirely RNA based ("RNA world") then later adapted to incorporate DNA and proteins. No other variants on this model managed to have descendants which survived to this day (to our knowledge)

 

As to the feasibility of non-DNA/RNA/protein based life, I'm not a chemist so I don't even want to venture a guess.

[Xyph]

On the base-element part of your question, Silicon (or Silicon-Oxygen) or Phosphorus-Nitrogen bases are the most commonly proposed alternatives to carbon for life elsewhere in the universe, as far as I know. Both, however, suffer from a far lower cosmic abundance than carbon, the latter especially.

 

Beyond that, I don't know nearly enough to say how well non-carbon bases would work, or whether there are alternatives to DNA-based life. I would guess, however, that the vast majority of extraterrestrial would be carbon-based, due in part to its sheer cosmic abundance but also because, from what I've read on the subject, it's just the element most suited by far to forming the complex molecules necessary for life to occur.

[Kermit]

I've read somewhere that it was possible to make variations of DNA that had a few tweaks here and there:

 

- Different amounts of strands. Triple helix. Quadruple helix?

- Different sugars instead of pentose, like hexose and such.

- Different nucleotide languages.

 

But in all those experiments they weren't as successful as DNA itself.

 

Hope that helped. As always there's Wikipedia.

[RyanJ]

Kermit, as far as I am aware all of those you have stated can be done too soem degree, right now we are still learning about oour own DNA so writing our own DNA code system is for the moment out of our ability I would think - or atleast in any useful scale.

 

Multiple helixes is interesting because it allows you to store more informaiton in less space... a very useful prospect.

 

As for the topic question, as posted by everyone else, shoure its possible though its unlikley that anything close too our DNA structure would be formed elsewhere.

 

Cheers,

 

Ryan Jones

[starbug1]

but does genetic information have to be stored in a helix, whether it is two-, three-, or four-stranded? Or does it even have to be composed of nucleic acids?

[RyanJ]

Or does it even have to be composed of nucleic acids?

 

I would not think so, I suppose you could develop your own system but it would probably not be very effective for life on Earth as ours has eveolved to perfectly suit our environment but shure I guess you could develop your own DNA system

 

Also, I don't see why it would have to be a helix, a helix is just a very efficient use of space

 

Cheers,

 

Ryan Jones

[Ophiolite]

I present an analogy: before the Pioneer and Voyager craft reached the outer planets we had very little idea about the character of their satellites. The consensus was that the larger ones would be pretty much like the moon. When we actually saw the diversity there, it blew fuses in the minds of every geologist, planetologist and astronomer. We just aren't to good at imagining, in any reliable and detailed way, what might be.

When we detect our first alien life, I think the same thing will happen. We sill be staggered and amazed by its diversity of character.

The good news is once we are faced with these realities we get pretty good at explaining them. It's our predicitive powers that are comparatively lacking.

 

And just to emphasise why we only have DNA based forms here [which isn't strictly true]. We DNAers ate up all the others.

[ecoli]

Thats a good analogy, Ophiolite. It certainly makes the desired point from a real situation.

 

We humans lack imagination, but perhaps because there are so many possiblities out there, that the though of finding something like ourselves out there is comforting. It's true that there an infinite variations for alien life, so it's not really possible for us to consider them all, so the work of an exobiologist would obviously need somewhere to base life forms off us... which would be us. Also, I'm sure Hollywood contributes to this as well.

 

I think the only movie that did a good job explaining why people and the aliens looked the same was Mission to Mars (I think that's right) where the humans were actually descendents of the martians.

[starbug1]

I'm not refuting that the realm of disverse alien life is beyond our comprehension; it probably is. But, when I was thinking about the componenents needed to trigger life, as it were, aren't the ingredients relatively similar? Meaning, a planet has to be within strict bounds and everything has to be just right (temp, atmosphere) to even start life. So wouldn't that mean an alien race would have to start from what we started from? Of course, this doesn't mean evolution works the same way, so we may not come out looking the same, but speaking of origins only.

 

And as ecoli mentioned, in Mission to Mars, even with remarkably homogeneous DNA, we, the descendents of Martians, evolve into something completely different in terms of appearance, and less sophisticated as well. So, with what we can comprehend, I think that as far as humans have evolved, if we were to encounter aliens, they wouldn't be completely unimaginable or incomprehensible. Science fiction writers, for one, have expanded greatly on this area as well as media and Hollywood. They may not be right, but just because of these things, we have at least a little experience in the matter.

[bascule]

I think it's certainly possible that there is life on other planets which uses mechanisms fundamentally the same as our own cells: DNA, RNA, and protein, encapsulated in a cellular container with complex, multicellular lifeforms built out of these cells.

 

Of course, I doubt the machinery of these cells would look anything like the eukaryotic cell...

[Ophiolite]

Part of the problem is that a lot of the really serious experimentation took place microscopically, very early in the Earth's history. There simply is no record (as yet detected) of what alternate pathways or chemicals were tried that failed either through pure chance or because in Earth's precise environment they were marginally less fit.

Maybe these alternate pathways are so poor they never even get started.

Maybe they get started, but are quickly overwhelmed by DNA etc.

We simply do not know --- yet. That's what makes it fun.

 

And bascule, we may be displaying the limits of our imagination if we restrict ourselves to thinking of cells.

Imagine viral like entities that inhabit lipid coated, organic rich, water droplets long enough to generate a few more of their ilk before the droplets dry out and the spores are spread on the wind till they encounter their next water droplet.