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Self-Replicating Molecules.
How did certain chemicals combine to produce the first self-replicating molecules?
Answers
We don't know. Writings on the subject are still full of the words 'possibly' and 'perhaps'.
17:56 Wed 13th Nov 2013
Here's a puzzler for you
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I argue in favour of random reactions having the potential for building complex molecules but hotch-potch polypeptides made up some L and some D amino acids evidently failed to send their 'descendents' down to the present day. Maybe they didn't fold up in the right way to be biologically active?
Presumably, a protein sequence made entirely from D amino acids could fold itself into a complete mirror-image enzyme but that would only function on the corresponding mirror image ligand(s). It therefore has no purpose in the L amino acid world. If any life forms ever arose from them, these also seem to have gone extinct.
http://
I argue in favour of random reactions having the potential for building complex molecules but hotch-potch polypeptides made up some L and some D amino acids evidently failed to send their 'descendents' down to the present day. Maybe they didn't fold up in the right way to be biologically active?
Presumably, a protein sequence made entirely from D amino acids could fold itself into a complete mirror-image enzyme but that would only function on the corresponding mirror image ligand(s). It therefore has no purpose in the L amino acid world. If any life forms ever arose from them, these also seem to have gone extinct.
Hypo; I find what you say about mirror-imaged amino acids really fascinating, I've just been trying to find an article about LH and RH amino acids, - one of them potentially arriving on Earth via meteorites, but I can't lay my hand on it, do you know more?
SIQ; No intention to be discourteous, I just think spontaneous life from primeval soup theories have been discredited, and there really is no evidence for its support.
SIQ; No intention to be discourteous, I just think spontaneous life from primeval soup theories have been discredited, and there really is no evidence for its support.
@Khandro,
the space dust aspect is specifically mentioned in the wiki article and the citation points to this article: -
http://
hope that helps
the space dust aspect is specifically mentioned in the wiki article and the citation points to this article: -
http://
hope that helps
http://
The above article may be of help. Interestingly it mentions that the amino acids present in genetic material with the oldest 'pedigree' are those produced by the Miller-Urey experiment. Although dozens of amino acids have been found in material from extra-terrestrial sources (meteorites and comets) these do not match the 'life' amino acids so well. The indication is that life did originate on Earth.
The above article may be of help. Interestingly it mentions that the amino acids present in genetic material with the oldest 'pedigree' are those produced by the Miller-Urey experiment. Although dozens of amino acids have been found in material from extra-terrestrial sources (meteorites and comets) these do not match the 'life' amino acids so well. The indication is that life did originate on Earth.
jomifl; Let us smoke the calumet and continue. :-)
You conclude from your Miller-Urey link that //The indication is that life did originate on Earth.// but I fail to see it in the article, what is that based on? Have you read Hypo's New Scientist link ? the French experiments seem to favour more an extra-terrestrial source of life.
You conclude from your Miller-Urey link that //The indication is that life did originate on Earth.// but I fail to see it in the article, what is that based on? Have you read Hypo's New Scientist link ? the French experiments seem to favour more an extra-terrestrial source of life.
jomifl; I have re-read the wikipedia Miller-Urey experiment again as you suggested and I still fail to see how you form your conclusion that it indicates "that life did originate on Earth." In fact the strongest assertion in there is under the heading; 'Extraterrestrial sources' which points to the Panspermis Hypothesis, indicating that life on Earth originated outside of its confines.
There is good support for this; "Life could spread from planet to planet or from stellar system to stellar system, carried on meteors. ”
—Stephen Hawking, Origins Symposium, 2009
There is good support for this; "Life could spread from planet to planet or from stellar system to stellar system, carried on meteors. ”
—Stephen Hawking, Origins Symposium, 2009
Khandro, I'll make it easy for you;
In recent years, studies have been made of the amino acid composition of the products of "old" areas in "old" genes, defined as those that are found to be common to organisms from several widely separated species, assumed to share only the last universal ancestor (LUA) of all extant species. These studies found that the products of these areas are enriched in those amino acids that are also most readily produced in the Miller–Urey experiment. This suggests that the original genetic code was based on a smaller number of amino acids – only those available in prebiotic nature – than the current one.[28]
I am not ruling out panspermia, I just think the Miller Urey experiment points toward the more likely origin of life. So far all is conjecture but who knows what some gem of scientific creative thinking might reveal.
In recent years, studies have been made of the amino acid composition of the products of "old" areas in "old" genes, defined as those that are found to be common to organisms from several widely separated species, assumed to share only the last universal ancestor (LUA) of all extant species. These studies found that the products of these areas are enriched in those amino acids that are also most readily produced in the Miller–Urey experiment. This suggests that the original genetic code was based on a smaller number of amino acids – only those available in prebiotic nature – than the current one.[28]
I am not ruling out panspermia, I just think the Miller Urey experiment points toward the more likely origin of life. So far all is conjecture but who knows what some gem of scientific creative thinking might reveal.
Ty for defending the scientific efforts from those of us.
I'd like to plod on and chat with Khandro later.
It's easier to understand now we've reached the DNA stage.
DNA is the only known "self-replicating" molecule in the universe although evolution has proceeded to introduce helper factors which keep in more accurate in it's function.
Many other molecules can be replicated many times but they need an independent template to copy from.
So let's stick to the "soup" theory although this "soup" may even have been solid (see later) and keep the chemistry primitive and hence easier to occur and then evolve from the basic origins.
Oh, I'm writing everything off the top of my head, based on my old learned bits - no reference-checks - in fact I've currently got one eye on the footy.
Regards,
SIQ.
I'd like to plod on and chat with Khandro later.
It's easier to understand now we've reached the DNA stage.
DNA is the only known "self-replicating" molecule in the universe although evolution has proceeded to introduce helper factors which keep in more accurate in it's function.
Many other molecules can be replicated many times but they need an independent template to copy from.
So let's stick to the "soup" theory although this "soup" may even have been solid (see later) and keep the chemistry primitive and hence easier to occur and then evolve from the basic origins.
Oh, I'm writing everything off the top of my head, based on my old learned bits - no reference-checks - in fact I've currently got one eye on the footy.
Regards,
SIQ.
We have seen that DNA is a double polymer of only 4 molecules: A,G.T,C. currently plus linker molecules. A & G form one chain and T & C the other. "A" hydrogen-bonds with "T" and "G" with "C".
So hydrogen bonds act as a "zip". So when they "unzip" they can select their complementary molecule and "zip" together to form 2 DNA molecules.
In primitive times "unzipping" and "zipping" could have occurred by heat changes or other simple physico/chemical changes.
But we need to speed up the rate of DNA chain formation to increase the credibilty of its formation and primitive evolution. Many factors can do this, including:
(a) Catalysis. You know all about this from cars' catalytic converters rapidly changing the exhaust fumes to more harmless chemcals;
(b) Concentating potential reactants mechanically or bagging them in semi-permeable bags;
(c) Heat at optimal temperatures e.g sunlight, volcanoes etc;
(d) Electromagnetic irradiation e.g. microwaves, UV etc.
Bye for now,
SIQ.
So hydrogen bonds act as a "zip". So when they "unzip" they can select their complementary molecule and "zip" together to form 2 DNA molecules.
In primitive times "unzipping" and "zipping" could have occurred by heat changes or other simple physico/chemical changes.
But we need to speed up the rate of DNA chain formation to increase the credibilty of its formation and primitive evolution. Many factors can do this, including:
(a) Catalysis. You know all about this from cars' catalytic converters rapidly changing the exhaust fumes to more harmless chemcals;
(b) Concentating potential reactants mechanically or bagging them in semi-permeable bags;
(c) Heat at optimal temperatures e.g sunlight, volcanoes etc;
(d) Electromagnetic irradiation e.g. microwaves, UV etc.
Bye for now,
SIQ.
