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I understand that all life forms on the planet are made from adenine, gauatine, cytosine and thymine, which chemically joined together to form RNA or DNA (correct me if I'm wrong). This goes on to form all complex life as we know it.

I was wondering if it was possible- even studied theoretically- that other life forms could exist made of different elements and compounds, perhaps let's say iron, cobalt or tungsten? Or are the 4 bases the only possible way of life as we currently know it?

83457
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    If we think of a cell as the unit of life, these constructs are made up of lipids, carbohydrates, proteins and nucleic acids. Of course, viruses are considered non-living, and are composed typically of just nucleic acid and protein. At that, we have to make a cutoff between what is living, what's non-living, and what constitutes one or the other. For reference, nucleic acid is DNA/RNA. The take-home point though, is that you need more than nucleic acid to get a living organism as far as knowledge contends; ergo we'd need more than an element/polymer. – CKM Mar 03 '15 at 22:47
  • You seem to have a severe misunderstanding of biochemistry. The 4 nucleotides you mention A, G, T, and C are used to make DNA, but in RNA, the T is replaced with uridine, U. Additionally, RNA can contain many modified nucleotides. Of course, there are many many more compounds in living organisms than just the nucleotides. I recommend reading some wikipedia articles to get a better understanding, such as on DNA, RNA, how they're related. – user137 Mar 03 '15 at 22:49
  • possible duplicate of http://biology.stackexchange.com/questions/90/life-without-dna ? – Mithoron Mar 04 '15 at 00:18
  • Nobody knows for sure, but search Google News for "Life on Titan". – jamesqf Mar 04 '15 at 20:18
  • @user137 I was aware of the U base. When I said all life forms are made of the four bases, I just meant a large amount – 83457 Mar 07 '15 at 20:24

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So this question is difficult to answer because it has some errors in it, in that lifeforms being dependent on rarely used elements is a different question than lifeforms using different DNA bases, but I will answer both.

So for the question about whether or not organisms could exist that use DNA bases not found in organisms on earth, the answer is certainly yes.[1,2]

The above reference shows a very elegant example of completely synthetic DNA bases being incorporated into E Coli and propagated in culture without providing any noticeable negative effects. This provides strong support that life on Earth developed around the same 5 bases (CTGAU) by chance.

As for whether or not organisms could rely heavily on elements other than H,C,N,O, and P, this is certainly possible and evident already here on Earth. Extremophiles are a general class of organisms that have some pretty interesting properties to them. Some metabolize sulfur or metals, others live in really extreme temperatures or in areas of high radiation.

So really yes in both cases, life can really take numerous shapes and forms even when it seems completely impossible for them to do so.

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