My name is LUCA - How single cells could have evolved

LUCA

It seems that one of the biggest problems with evolution theory is to answer the question of the development of a single cell. Oparin, the arch evolutionist claimed that this was the single biggest problem for evolutionists to answer. I have trawled through Wiki to find the best theories of the formation of the single cell and have read up on the Wachterhauser theory and its modified black smoker/LUCA theory – LUCA standing for Last Universal Common Ancestor as the best theory so far. It would be nice to invite comments as I am playing the devil’s advocate.

LINK

Miller and Urey experiment

Miller and Urey’s famous experiment copying the very early environment on the Earth showed amino acids (the building blocks of proteins found in muscle; and in large molecules called enzymes which control cell metabolism) were made in a mixture of gases - methane, ammonia and hydrogen with a bit of lightning thrown in.

PROBLEM: These experimental results were under threat when other experimenters postulated that the levels of oxygen theoretically present in the ‘real’ scenario would have destroyed the amino acids as they formed. Despite modifications to the experiment there is no overwhelmingly convincing further development.

Wächtershäuser's iron-sulfur world theory

"Wächtershäuser systems" come with a built-in source of energy, sulfides of iron and other minerals (e.g. pyrite). The energy generated from redox reactions (giving of electrons by some ions and receipt of electrons by other ions) should be available for the formation of small chains of amino acids joined together with peptide bonds (peptide bonds are strong covalent bonds linking chains of amino acids together).

Wachterhauser’s experiment hypothesised that the peptides would start to speed up the reactions to make other newer and novel sets of peptides. This chain of events that would lead to the first cell life form.

PROBLEM: The experiment turned out a tiny amount of dipeptides (two amino acids joined together) and an even tinier (0.1%) of three amino acids joined together (tripeptides). The dipeptides were quickly broken down under their experimental conditions – the experiment had NOT yielded long-lasting building blocks for life.

Black smokers lead to LUCA

The latest modification of the iron-sulfur-hypothesis was provided by Martin and Russell in 2002. According to their scenario, the first cellular life forms may have evolved inside so-called black smokers at seafloor spreading zones in the deep sea. The above researchers imagined caverns coated in thin layers of iron sulfide walls to solve the problems faced by Wachterhauser:

The model allows for a succession of different steps of cellular evolution (prebiotic chemistry, monomer and oligomer synthesis, peptide and protein synthesis, RNA world, ribonucleoprotein assembly and DNA world) in a single structure, facilitating exchange between all developmental stages. These steps would all take place in the micro-caverns as a protective structure where chemicals would be much more likely to collide with each other to form chemical reactions. There would be a flow of water bringing in fresh chemicals and large temperature zones of high or low temperature to encourage formation of the building blocks of life.
The last evolutionary step would be the synthesis of a lipid membrane that finally allows the organisms to leave the microcavern system of the black smokers and start their independent lives.

PROBLEM: Even if we get to the point where a LUCA is ready to leave as a single cell, where does the membrane come from and how does the cell perform cell division without the enzymes needed to copy the genetic material.

Very interesting reading, thank you. I'm looking forward to the day when they figure out what the event that sparked life on our planet was.

How do we know that one of the many meteorites and comets that smashed into the early earth wasn't carrying life in an encysted or spore form, from somewhere else? Of course that doesn't solve the problem of where THAT life came from and how IT evolved, but it could explain how life seemed to spontaneously start here.

We may actually never know HOW it started. Even with the best equipment, I am not entirely convinced that scientists can fully recreate the conditions of the early earth. There may be something they are overlooking that is not present on earth today.

Please keep posting these hypotheses about how life began on earth. It is such an intriguing puzzle.

I just thought I'd take a break from meta-analysis of evolutionary flaws and appreciate some of the good science that is out there. This is the best account that I have read of the how a single cell could have evolved. I don't have to agree with it but I can admire a beautiful hypothesis - the same as the next man.

In a sad and desperate attempt to boost some interest in this post, I am forced to insert a link to Suzanne Vega's song called 'My name is Luka' but I don't think it was about Last Universal Common Ancestor theory (but you never know...)
My name is Luka

Interesting topic. I read it a few days ago but didn't have time to reply here until now.

I think that life obviously existed before cells, under the form of replicating molecules that predated RNA and DNA. A bit like some cristals that can replicate but are not yet lifeforms.

Again I think cellular structures are the result of a long evolution to protect the replicator/pre-DNA. The first cells would have been merely a simple spherical shapy thing around the replicator, with no membrane, no organs, no cytosqueleton , etc.

To think the first cells would be similar to the cells we observe today would be like thinking the wright brothers would have built an F-35 instead of their flying piece of wood

Definitaly the most difficult question we have to answer, after where the universe came from, and where whatever was before the universe came from, and whatever was before the thing that made the thing that made our universe come from too

[edit on 1-6-2007 by DarkSide]

We have all evolved from very very small things in the sea. Why i think that well because it just makes more sense to me rather than a tall white guy with a robe and long hair creating 2 people called Adam and Eve. Oh and he not create the dinosaurs when we no they existed. Evolution

You ever noticed how people who believe in Creationism look really unevolved? You ever noticed that? Eyes real close together, eyebrow ridges, big furry hands and feet. "I believe God created me in one day" Yeah, looks like He rushed it.