There has actually been quite a lot of interesting research and progress on both of those issues, but I'm too tired right now to go Googling for it (I've been up all night, about to go to bed now). Suffice to say that although the processes by which they arose are not fully understood yet, there are already plausible precursor systems, and biochemical evidence of the nature of the earlier stages.
And remember, in 1900 it was "difficult to see how" the Sun could produce so much endless energy. I actually read a creationist book from that era which argued that since no known (chemical) process could produce so much energy for thousands of years, it must be proof that God was actively running it. Needless to say, science went on to learn how such natural processes actually work without direct divine intervention to keep them running each day.
For now, here's a previous post of mine concerning research into the evolution of the Krebs metabolic cycle:
What do you have concerning the development of the Krebs cycle?Ooh, glad you asked, now I have a good excuse to post this cool animation of the Krebs cycle:
To read up on the evolution of the Krebs cycle (also known as the citric acid cycle), a good starting point is:
The puzzle of the Krebs citric acid cycle: assembling the pieces of chemically feasible reactions, and opportunism in the design of metabolic pathways during evolution, Melendez-Hevia E, Waddell TG, Cascante M, J Mol Evol. 1996 Sep;43(3):293-303A portion of the abstract:Study of the evolutionary possibilities of each one-taking the available material to build new pathways-demonstrates that the emergence of the Krebs cycle has been a typical case of opportunism in molecular evolution. Our analysis proves, therefore, that the role of opportunism in evolution has converted a problem of several possible chemical solutions into a single-solution problem, with the actual Krebs cycle demonstrated to be the best possible chemical design. Our results also allow us to derive the rules under which metabolic pathways emerged during the origin of life.From the body of the article:In the evolution of the metabolism, the achievement of the fundamental steps of the Krebs cycle was not difficult at all. Almost all of its structure previously existed for very different purposes (anabolic), and cells had to add just one enzyme (succinyl-CoA synthetase for the transformation of succynol CoA into succinate) to convert a collection of different pathways into the central cyclic pathway of the metabolism. This is one of the most clear cases of opportunism we can find in evolution.Also see (link goes to full text):[...]
The Krebs cycle has been frequently quoted as a key problem in the evolution of living cells, hard to explain by Darwin's natural selection: How could natural selection explain the building of a complicated structure in toto, when the intermediate stages have no obvious fitness functionality? This looks, in principle, similar to the eye problem, as in 'What is the use of half an eye?' (see Dawkins 1986, 1994). However, our analysis demonstrates that this case is quite different. The eye evolved because the intermediary stages were also functional as eyes, and, thus the same target of fitness was operating during the complete evolution. In the Krebs cycle problem the intermediary stages were also useful, but for different purposes, and, therefore, its complete design was a very clear case of opportunism. The building of the eye was really a creative process in order to make a new thing specifically, but the Krebs cycle was built through the process that Jacob (1977) called 'evolution by molecular tinkering,' stating that evolution does not produce novelties from scratch: It works on what already exists. The most novel result of our analysis is seeing how, with minimal new material, evolution created the most important pathway of metabolism, achieving the best chemically possible design. In this case, a chemical engineer who was looking for the best design of the process could not have found a better design than the cycle which works in living cells.
A mitochondrial-like aconitase in the bacterium Bacteroides fragilis: Implications for the evolution of the mitochondrial Krebs cycle, Anthony D. Baughn and Michael H. MalamyWhile on the subject, I can't resist providing a link to this nifty site I ran across while digging up the above links. It's a multi-page animated tutorial on cellular respiration (including the Kreb's cycle), and it's a great introduction to the whole subject. It also makes fascinating observations like, for example, the fact that our critical dependence upon oxygen, and our lungs, red blood cells, and all related systems, don't actually play any direct role in our cellular metabolism -- they exist solely in order to remove electrons from the mitochondrial electron transport system, a minor (but vital) sideshow in the actual core metabolic processes of the cell. We don't need oxygen for energy or metabolism, as many people presume, we just need it to keep the assembly line clear...That same website has other cool biology tutorials, hit the "outline" link at the bottom to see an index.
Yet more reconstruction of the evolution of the Kreb's cycle:
The Molecular Anatomy of an Ancient Adaptive Event: Protein engineering identifies the structural basis of a 3.5 billion-year-old adaptation, Antony Dean, American Scientist, Volume: 86 Number: 1 Page: 26 DOI: 10.1511/1998.1.26In short, the Krebs cycle arose as a relatively minor modification to pre-existing cellular biochemical processes which were being used for amino acid synthesis and early iron-based metabolism.Since the next question will undoubtedly be, "where did the iron-based metabolism come from", next we will visit:
The universal ancestor was a thermophile or a hyperthermophile: tests and further evidence, Di Giulio M., J Theor Biol. 2003 Apr 7;221(3):425-36...which is only one of the recent confirmations of this model of the origin of life as we know it:On the origins of cells: a hypothesis for the evolutionary transitions from abiotic geochemistry to chemoautotrophic prokaryotes, and from prokaryotes to nucleated cells, William Martin and Michael J. Russell, Phil. Trans. R. Soc. Lond. B, DOI 10.1098/rstb.2002.1183A related observation is:"The oldest of these proteins was ferredoxin, a biosynthesis enzyme that contains iron-sulfur clusters and that transfers electrons (hydrogen-atom equivalents). This protein he reconstructs as having a negatively-charged tail; this can stick to positively-charged objects like mineral surfaces with their metal ions -- which is consistent with the view of Gunter Wachtershauser that life originated from iron-sulfur-associated chemical reactions on mineral surfaces, and that the Krebs Cycle dates from this time. Note that the Krebs Cycle's members are all acids -- negatively-charged ions -- meaning that they can stick to mineral surfaces."In short, life most likely originated in iron monosulphide pockets around hydrothermal ocean vents.
-- from this webforum discussionFinally, since someone is bound to mention the creationists' favorite biochemist Behe, it seems appropriate here to point out one of Behe's many whoppers. In his book "Darwin's Black Box", he wrote:
"There has never been a meeting, or a book, or a paper on details of the evolution of complex biochemical systems."What planet is *he* living on? There have been countless statements by biochemists expressing their bafflement at how Behe could make such a transparently false claim.
[...]
"In effect, the theory of Darwinian molecular evolution has not published, and so it should perish"One web author points out that a simple MEDLINE search turns up *thousands* of such papers -- so what's Behe's excuse? But my main reason for bringing up this particular web page is that it's a really decent compilation of links to papers on various aspects of molecular evolution, and a good starting point for finding answers to the kind of question you pose. That page is Behe's empty box: alive and published -- Some published works on biochemical evolution.
