pgrmdave Posted February 5, 2005 Report Share Posted February 5, 2005 I think that it may depend on how basic life starts. If it starts as simple self-replicating proteins, than I think that the probability is quite high, if it starts as DNA, then I think that the probability is quite low. Link to comment Share on other sites More sharing options...
TeleMad Posted February 5, 2005 Report Share Posted February 5, 2005 I think that it may depend on how basic life starts. If it starts as simple self-replicating proteins, than I think that the probability is quite high... Why do you think it is high? 1) No prebiotically plausible experiment has yet to produce a self-replicating protein. 2) If you already have self-replicating proteins, it's difficult to explain how nucleic acids would get added into the system (one reason being that proteins are much better catalysts than RNA). It makes more sense (and there are lines of circumstantial evidence that support the notion) for life to have started as self-replicating RNA, with many of the ribozymes being replaced over time by "better" proteinaceous enzymes that happened to evolve. Link to comment Share on other sites More sharing options...
alxian Posted February 9, 2005 Report Share Posted February 9, 2005 titan is how far from the sun?? how much radiant energy is titan producing? forget titan look at the heated moons of jupiter like europa for anaerobic bacteria and io for possible traces of sulphur bacteria (but io for now seems to lack a liquid solvent) venus's atmosphere, jupiters atmosphere (which according to science fact and fiction has an earth normal layer (temperature and pressure)). other extraplanetary places in sols domain? um.. i'd say the upper layers of the mercurian crust, where asimov claims their may be solvents in the form of liquid metals. but pretty much anywhere else i can think of would be far too cold (for solvents to flow freely amoung volatile and complex chemical compounds (like amino acids)(which would require at least some amount of heat (which can still be below freezing tempatures, as long as there is a solvent present)) Link to comment Share on other sites More sharing options...
TeleMad Posted February 10, 2005 Report Share Posted February 10, 2005 pgrmdave: I think that it may depend on how basic life starts. If it starts as simple self-replicating proteins, than I think that the probability is quite high... Telemad: Why do you think it is high? 1) No prebiotically plausible experiment has yet to produce a self-replicating protein. 2) If you already have self-replicating proteins, it's difficult to explain how nucleic acids would get added into the system (one reason being that proteins are much better catalysts than RNA). It makes more sense (and there are lines of circumstantial evidence that support the notion) for life to have started as self-replicating RNA, with many of the ribozymes being replaced over time by "better" proteinaceous enzymes that happened to evolve. Another problem with the idea of self-replicating proteins is their polymerization, in that their amino acid monomers do not form complementary pairs like the nucleotides of nucleic acids do. When Watson and Crick determined the double-helical structure of DNA and its use of comlementary bases, they immediately realized these made replicating DNA quite straightforward. Nature just has to unzip the double helix and use each single strand as an informational template to reform its missing, complementary partner. Proteins don't behave this way. Unlike DNA, where an A is 'always' paired with T and a C is 'always' paired with a G, proteins don't have monomers that form complementary pairs. Proteins can't simply unzip and then use each half as an informational template to reform the missing halves. Link to comment Share on other sites More sharing options...
alxian Posted February 10, 2005 Report Share Posted February 10, 2005 so where did proteins come from? someone whispers god.. Link to comment Share on other sites More sharing options...
TeleMad Posted February 10, 2005 Report Share Posted February 10, 2005 so where did proteins come from? someone whispers god.. According to the RNA World theory, from RNA. The enzymatic portion of ribosomes - the part that possess peptidyl transferase activity - is composed of RNA, not protein. So the idea is that once self-replicating RNA arose and started evolving accessory functional sequences, RNA molecules catalyzed the polymerization of amino acids into proteins (RNA would have also coded the amino acid sequences). From this all-RNA construct arose a full fledged ribosome. Over time, many of the RNA molecules were replaced by proteins; present ribosomes consist of both RNA and proteins. Link to comment Share on other sites More sharing options...
alxian Posted February 10, 2005 Report Share Posted February 10, 2005 mitochondria? developed in cells or symbiotic relationship formed way back when? Link to comment Share on other sites More sharing options...
pie Posted February 10, 2005 Report Share Posted February 10, 2005 I suspect that if there is life in the universe, it's only jurasic in nature. - The change of intelligent life is a freak event. - As life on earth, we are the freak, and the universe is our "freak show." Link to comment Share on other sites More sharing options...
Tormod Posted February 10, 2005 Report Share Posted February 10, 2005 mitochondria? developed in cells or symbiotic relationship formed way back when? Please, alxian, are you capable of writing slightly more insightful posts? This is a discussion forum, not a hit-and-run fun fair. Please take part in the discussion or stay out of it. There is a fine line between being funny and acting funny. Link to comment Share on other sites More sharing options...
TeleMad Posted February 12, 2005 Report Share Posted February 12, 2005 mitochondria? developed in cells or symbiotic relationship formed way back when? According to Lynn Margulis's endosymbiont theory (endosymbiotic hypothesis, or similar), which is now "accepted as textbook orthodoxy", mitochondria were once free-living prokaryotes that were engulfed by another prokaryote: but instead of being digested, the two formed a mutualistic symbiotic relationship. Over time, each evolved such as to become so heavily dependent upon the other - host on endosymbiont and endosymbiont on host - that they both lost the ability to live separately: hence was born the mitochondrion. Chloroplasts are also formerly free-living prokaryotes - probably cyanobacteria - that formed a mutualistic symbiotic relationship with their engulfer. Link to comment Share on other sites More sharing options...
MortenS Posted February 12, 2005 Report Share Posted February 12, 2005 The theory of endosymbiosis is well supported by evidence along several lines, some are indirect and circumstantial, others are more direct. 1. DNA in mitochondria and chloroplasts are circular, just as in prokaryotes.2. DNA in mitochondria and chloroplasts are naked (no histones), just as in prokaryotes3. rRNA in mitochondria and chloroplasts resemble the bacterial rRNA more than the eukaryote rRNA.4. Phylogenetic analysis of of several genes in the mtDNA strongly indicates a close relationship to alpha-proteobacterias such as Rickettsia 5. Phylogenetic analysis of several genes in chloroplast DNA strongly indicates a close relationship with cyanobacteria.6. The inner membrane of mitochondria and chloroplasts have enzymes and transport systems that resemble those on modern prokaryotes. There are still data pouring in on the relationship between organelles such as mitochondria and chloroplasts and the prokaryotes, and there are still much to be learned. While the support for the relationship between the organelles and the prokaryotes are strong, there is still some ambiguity when it comes to the ancestor the eukaryotic cell itself, and the origin of the nucleus, and the eukaryotic genome. The most recent theory, supported by both molecular evidence and other lines of evidence, is that the eukaryotic cell originated from Archaea. Link to comment Share on other sites More sharing options...
TeleMad Posted February 12, 2005 Report Share Posted February 12, 2005 And if anyone thinks the idea of one microbe engulfing another but not digesting it, but instead the two forming a symbiotic relationship, is implausible... "Some strains of the complex ciliated protist called Paramecium that we have met earlier have engulfed tiny, single-celled green algae. Hundreds of algae can live happily inside a single Paramecium, photosynthesizing and providing themselves and their host with essential nutrients. When the paramecia are grown in the dark, they eventually lose their algae, but if light is reintroduced and they are presented with new algae, the symbiosis is reestablished." (The Spark Of life: Darwin and the Primeval Soup, Christopher Wills and Jeffrey Bada, Persus Publishing, 2000, p193) The authors give other examples of such endosymbiotic relationships that can be directly examined in the lab: the discussion runs from page 192 to 198. Link to comment Share on other sites More sharing options...
C1ay Posted February 15, 2005 Report Share Posted February 15, 2005 Are WE the only life in the Universe? IMO, NO! I think it is a conceited view for mankind to think that he alone is the only intelligent life in an infinite universe with infinitely many planets like our own. Casting infinity aside though, one must still concede that the finite universe as we know it contains billions of galaxies each with billions of stars. The odds would seem to be greatly in favor of there being many worlds like our own. Link to comment Share on other sites More sharing options...
ldsoftwaresteve Posted February 15, 2005 Report Share Posted February 15, 2005 Clay, I'm jealous. That's the best quote I've ever seen. I think you should correct it to say, "There are only 11 kinds of people in the world. Those who understand binary, those who don't, and those who think they do but don't." Did you create it? If you did, I am totally humbled. Link to comment Share on other sites More sharing options...
C1ay Posted February 15, 2005 Report Share Posted February 15, 2005 "There are only 11 kinds of people in the world. Those who understand binary, those who don't, and those who think they do but don't." Did you create it? If you did, I am totally humbled. I actually believe there is a future for tertiary logic. At times I have used a quote very similar to your suggestion, ie, "There are only 10 kinds of people in the world. Those who understand trinary, those who don't, and those who think they do but don't." Link to comment Share on other sites More sharing options...
ldsoftwaresteve Posted February 15, 2005 Report Share Posted February 15, 2005 C1ay, lmao! Beautiful, just beautiful. Now I understand your avatar. Very nice to meet you. Link to comment Share on other sites More sharing options...
C1ay Posted February 15, 2005 Report Share Posted February 15, 2005 C1ay, lmao! Beautiful, just beautiful. Now I understand your avatar. Very nice to meet you. Glad you like it. Nice to meet you too. BTW, a fun screen saver and conversation starter is to set the moving text in your screen saver to 1 + 1 = 10. I find many family and friends just can't think outside of base 10 even if you explain it to them. Link to comment Share on other sites More sharing options...
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