What happened leading up to the first single-celled organism?

[Realitycheck]

What is the state of theory regarding the steps leading to the creation of the first single-celled organisms? What I have come up with on my own are the development of organic compounds into pseudo-organisms that can't necessarily be classified as living beings, until cold fusion takes place or lightning strikes and the Frankenstein effect takes place or something like that. I hate to sound like a preacher, but I think there comes a point where you have to accept that there must be a grand design driving it all in order for it to take place, whether it is directly willed or simply an involuntary process in the growth timeline of a planet with the characteristics of ours. My knowledge on the subject is very limited, but I was wondering what other people believe.

[Realitycheck]

Looking for an example of almost-living things or potential preliminary components of "cells" that don't have DNA?

 

Check out these things:

 

http://en.wikipedia.org/wiki/Prions

 

Maybe we get some kind of symbiotic relationship going on with one of these things and something else like it but much different?

 

 

(I know what some of you are probably thinking. If there was a God, why didn't he do it much faster, like in 7 days? It's really a moot point.)

[bombus]

coacervates.

 

An on the other point. Maybe there is a grand design, but any God worth his salt would have put a design in place long before life emerged. God wouldn't go around designing slugs tongues, and cockroach legs, and fish gills, and monkey ears. He'd have just put in place some laws (like the Laws of Nature) and let nature do it all for him.

 

My God is very clever!

[ecoli]

No more talking about God... go to TFN for that.

 

Also, you may want to look up a couple of things.

 

Like the Miller-Urey experiment (http://en.wikipedia.org/wiki/Miller-Urey_experiment)

and protobionts http://biocab.org/Protobiont.html

[SkepticLance]

We are slowly learning possible ways biogenesis could have taken place. The Miller experiment showed that organic molecules will form in a world with methane, CO2, water etc, when energy is applied, such as by lightning, strong UV, asteroid collision etc. Thus, any planet that has such an atmosphere, and is of the right temperature, permitting liquid water, will end up with organic molecules dissolved in the pools of liquid water.

 

Beyond that, things are less clear. We know that certain minerals, such as calcite, will cause certain organic molecules to 'line up' on the mineral surface, allowing them to join to form simple polymers. This may have led to the first complex molecules.

 

Some of those complex molecules are likely to have acted as catalysts, to assist in the formation of more polymers. Fatty acids have a habit of forming into spheres, which can entrap some of these polymers, forming something similar to the membrane of a cell around cytoplasm.

 

This is about as far as we can go, with current knowledge, although there is a great deal more detail known than I have stated. Somewhere, the interacting mass of organic molecules and polymers have created a self-replicating molecule that can 'feed' on the organic material around it, and multiply. If such a molecule is subject to chemical changes that are passed on to the 'daughter' molecules, then evolution by natural selection becomes possible on a molecular level. And life has begun.

[Realitycheck]

The experiment used water (H2O), methane (CH4), ammonia (NH3) and hydrogen (H2). The chemicals were all sealed inside a sterile array of glass tubes and flasks connected together in a loop, with one flask half-full of liquid water and another flask containing a pair of electrodes. The liquid water was heated to induce evaporation, sparks were fired between the electrodes to simulate lightning through the atmosphere and water vapor, and then the atmosphere was cooled again so that the water could condense and trickle back into the first flask in a continuous cycle

 

At the end of one week of continuous operation Miller and Urey observed that as much as 10-15% of the carbon within the system was now in the form of organic compounds. Two percent of the carbon had formed amino acids, including 13 of the 22 that are used to make proteins in living cells, with glycine as the most abundant. Sugars, lipids, and nucleic acids (such as DNA, RNA, and ATP when phosphate was present) were also formed. As observed in all consequent experiments, both left-handed (L) and right-handed (D) optical isomers were created in a racemic mixture.

 

The molecules produced were simple organic molecules, far from a complete living biochemical system, but the experiment established that the hypothetical processes could produce some building blocks of life without requiring life to synthesize them first.

 

I have the hardest time seeing how such complex compounds as DNA could form from an experiment such as this.

[SkepticLance]

To agentchange.

 

DNA did NOT form as simply as the Miller experiment. The Miller process represents only the first stage. It is likely the origin of the simple organic compounds such as purines and amino acids, which for the building blocks for polymers etc, which after a number of other changes lead to something like DNA.

 

As in my previous posting, it takes minerals, fatty acids, simple polymerisation, catalyst formation etc to lead to even the simplest replicating molecule. It is the stages after the Miller experiment type reactions that scientists are still studying and trying to simulate, and which are the key to the first life.

[lucaspa]

What is the state of theory regarding the steps leading to the creation of the first single-celled organisms? What I have come up with on my own are the development of organic compounds into pseudo-organisms that can't necessarily be classified as living beings, until cold fusion takes place or lightning strikes and the Frankenstein effect takes place or something like that. I hate to sound like a preacher, but I think there comes a point where you have to accept that there must be a grand design driving it all in order for it to take place, whether it is directly willed or simply an involuntary process in the growth timeline of a planet with the characteristics of ours. My knowledge on the subject is very limited, but I was wondering what other people believe.

 

http://www.theharbinger.org/articles/rel_sci/fox.html

 

Simple chemical reactions lead to the first living organisms. These did not have directed protein synthesis. That evolved later.

[lucaspa]

I have the hardest time seeing how such complex compounds as DNA could form from an experiment such as this.

 

They didn't. What Miller-Urey got were the building block chemicals that compose proteins and DNA.

 

DNA and proteins are polymers of more simple molecules. Proteins are polymers of amino acids. DNA/RNA are polymers of nucleic acids. Nucleic acids, in turn, are composed of a sugar, a base, and phosphate joined together by covalent bonds. In RNA the sugar is ribose. In DNA it is deoxyribose (missing an -OH group). They then have the "bases" that are adenine, thymine, cytosine, uridine, and guanine.

 

Miller-Urey took methane, carbon dioxide, water, ammonia, and hydrogen and, thru simple chemical reactions, got sugars, amino acids, and bases. Other chemical reactions (in other circumstances) combine the sugars and bases to make nucleotides (then the nucleotides to make DNA/RNA) and the amino acids to make proteins.