livescience.com — A bacterium living in special cells inside an insect has the smallest genome of any known cellular lifeform, a new study finds. With only about 160,000 base pairs of DNA, the genome of Carsonella ruddi [image] is less than half the size thought to be the minimum necessary for life.
Oct 12, 2006 View in Crawl 4
langfordOct 13, 2006
This creature does reproduce on it's own however. It may not produce all the proteins it needs to live, but neither do humans. What it lacks, it gets from it's food, which would be the insect's material. It still fulfills the requirements to be considered living, if only barely. <a class="user" href="http://en.wikipedia.org/wiki/Life#A_conventional_definition">http://en.wikipedia.org/wiki/Life#A_conventional_definition</a> Some might say that a virus deserves to be called living too, but what can I say, untestable definitions are subject to interpretation, and the line has to fall somewhere. I don't think a viruse resonds to stimuli either, except for maybe chimical based stimuli.
democracysucksOct 13, 2006
Theoretically, the smallest living organism would consist of 124 proteins. This is much smaller than what we've actually found, but this is what scientists guess would be the smallest. Now, living organisms consist ONLY of L-amino acids, and no D-amino acids (just has to do with orientation). Outside of a living thing, the proteins change to 50% L and %50 D, no matter what we do to try to stop them. Even if we START with all L-forms, they change to D-forms. So somehow, without intelligence (even though we can't do it today WITH intelligence), 100% L-forms would have to be found and maintained and put together just right to create a chemical similarity to living organisms. So let's say we had 1031 earths in the universe. That's 100000000000000000000000000000000 earths in the universe, each with oceans of, instead of water, amino acids. EVERY molecule in these oceans, we'll say, is an amino acid. Let's say every single amino acid in each ocean of each earth combined with another amino acid every second for 10 billion years, non-stop. The likelihood that 100% L-amino acids would ever form to create the smallest 124 proteins is 1 to 1078436 against. I don't have enough time to type all those zeros, but you get the picture. And that's not even being picky about which proteins you get (very few of the thousands of proteins we know could be used in these living organisms that supposedly formed). Now, the law of probability says anything that is 1 to 1050 against will never happen, though it's been recently accepted that anything 1 to 1020 against will never happen, no matter what. Looks like even just L-proteins could never form. That's forgetting about D-sugars, cell organelles, atmospheric conditions that would destroy anything that DID form the instant it happened, etc.
xirtoOct 13, 2006
@Anpheus: Introns are not considered "junk DNA" anymore. There is now evidence that introns have many functions such as gene expression regulation.
rbowesOct 13, 2006
The human genome is about 3 BILLION base pairs long. Good luck compressing that to 150,000, thats a 20,000 fold compression.
hegemonyOct 14, 2006
Actually he's not very well versed in biochemistry, kakapu4u (your name makes me giggle).@democracyWhere would you get these ideas? Have you taken a degree in biochemistry? I'd bet not since that was entirely wrong. Here are the main problems with your argument (which I suspect is copied and pasted). The conversion of L-Amino Acids to D-Amino Acids is not complete. In fact it's not close. It exists in an equilibrium governed by Le Chatelier's Principle. I have a jar of L-Arginine in my lab if you don't believe me.Also, your assumption that an amino acid forms a bond every second is WAY off. An entire protein (even globular proteins) folds completely in about 1 microsecond. Most of the folding takes place in the first 60 nanoseconds. Things happen very fast on the molecular level. Next, you completely ignore any catalytic action taken by any of these proteins. And you skipped right from your Amino Acid sea to 124 proteins with no explanation. And finally, your misunderstanding the number of conformations a protein can have. Sure you can calculate all these different orientations (phi-psi angles) that amino acids can take on. But most of them are impossible because of steric hindrance. Only thermodynamically favored bonds will form and bonds can sample conformations at the rate of 10^13 per second. This is known as the energy surface model in which functional conformation is obtained as proteins approach their lowest energy state.
Closed AccountOct 14, 2006
Chloroplasts and mitochondria are symbiotic bacteria living inside eukaryote cells, much like this reported bacterium does. The mitochondrion genome is about 15000 bases, one tenth of this "smallest genome".Also, as has been pointed out, these organisms have minute genomes because they a) have no redundancy in the genome and b) have outsourced a lot of their protein production to the host cell.Has anyone managed to get DNA out of a nanobacterium yet?
tmcdiggOct 14, 2006
there is still alot we don't know about the requirements of life, much less to say "ultimate minimum requirements"NoOne has invented equipment to see micro life, much less understand how it works or issue wonderfully intelligent ideas on the subject