The Origin of Life

Author: Stanislav Mitichkin (Russia, 2010)

Summary: * The origin of the first cells from simple replicators. * The transition from the RNA-world to the protein-world. * The key role of RNA-splicing as a producing factory.

1. In the beginning, there was a primordial soup, where a REPLICATOR appeared. It was already alive.

It appeared very simply and naturally. Imagine the ancient Earth. It has water with various simple organic molecules (nucleotides, amino acids), which can't replicate themselves. There are hot springs of water in nearby volcanoes. The Earth goes around the Sun and spins around its own axis, so there are days and nights. That's enough.

And now a miracle happens.

In the water under the ultraviolet radiation, the nucleotides (A, G, U, C) join together into a chain by covalent bonds. The Sun is setting and the water is cooling. The chain stops growing and the second chain starts assembling out of the free nucleotides as bricks. They connect together by weak hydrogen bonds according to the principle of complementarity.

A day is dawning, the Sun is warming, the water temperature is up to ~80 degrees Celsius (it's a hot spring, right?) and the hydrogen bonds are broken. Now we have two separate complementary chains. The Sun is shining with ultraviolet radiation and the chains are growing with the next nucleotides by covalent bonds.

A night is coming and the water is cooling. The chains are again connecting complementary bricks. And it goes on. In the night the chains connect to the bricks, during the day they separate. Connecting the bricks at nights, separating during the days. We now have a REPLICATION form through the natural way.

Another simple example. Let's assume we have a short RNA-chain: AGUC. Say, it appeared during the day by a random combination of molecules (this is quite probable).

At night it creates a complementary chain: AGUC UCAG

During the day the water warms, the hydrogen bonds break and divides them into two chains: AGUC and UCAG

The next night it again creates a complementary chain, but now two of them:




During the day they separate again and start growing under the ultraviolet radiation: AGUCAGUC UCAGUCAG

And now we have a replication process started…

2. Then ribozymes appear.

So, the chain becomes longer and makes complementary connections to itself. The tails of the chain join each other. Or second quarter joins the third quarter. Now we have got a secondary molecular structure as a result. It's able to fold up and take part in the catalysis. The molecule accelerates its own replication (or do it for the unfolded neighbours)

How really it was in detail maybe no one would know. However, lets just assume that the replication accelerated. Before we had only 2 chains around the clock, now we have 2000 chains during the same time. Accelerating of a chemical reaction by 1000 times is a trifle. The modern protein enzymes speed up chemical reactions by millions or hundreds of million times, but we will get to them later.

So, the process is speeding up. The replication accelerated amazingly and it doesn't depend on a day-night cycle anymore. However, it needs the energy income from the hot water and the ultraviolet radiation of the Sun.

3. Mutations and the natural selection. We already have an ancient copier/xerox that multiplies molecules in a Positive-Negative-Positive way. However, sometimes errors happen. Not always the complementarity keeps on at 100%. Therefore we get a variety. The natural selection begins to act. Only the ones, who can replicate and do it FASTER, survive. It means they have a more perfect catalytic ability of their own replication.

4. Now lets assume one of «error» replicator's copies gained an ability to cut itself (self-splicing). This is not any fantasy here. In fact, it is proven that some RNA molecules can cut themselves in various ways (Tested in vitro).

Let's look at intermediates results. We have a PRODUCING system, that can theoretically produce any product in a form of RNA molecules, including such of them that have catalytic abilities (we are interested only in such molecules, because a life itself is an amazingly accelerated chemical reaction). This producing system, or in other words a FACTORY, started to produce (cut away from itself) various kinds of RNA, that didn't code proteins yet. The RNA-factory gradually diversified its assortment.

Thanks to some key events the transformation to a protein world happened slowly:

* Ribosome RNA has been produced, which makes an active center of ribosomes. It catalyzes the forming of a peptide bond between amino acids. In the beginning it worked without any program, connecting amino acids by chance.

* Transfer RNAs have been produced, which transport amino acids to a proto-ribosome and implements a genetic code (nucleotides to amino acids). The proteins started being produced by program coded in RNA.

* Nucleoproteins appeared, which are complexes made of RNA and proteins. They became more and more sophisticated because of new kinds of proteins.

Ineffective ribozymes made of RNA are replaced by effective protein enzymes, produced by the program written in RNA. It is increasing the speed and the accuracy of RNA copying, and the accuracy of protein reproduction.

The transformation to a protein world finished. However, even today RNA takes part in the key and vital processes in every single cell.

Then DNA appeared as a reliable storage of information.

5. RNA turns into DNA by changing one nucleotide (uracil to thymine) and one simple sugar (ribose to deoxyribose). The single-chained RNA turns into the double-chained DNA. It increases the security of information, its chemical resistance, and provides an opportunity to correct mistakes, restoring the data from the second spiral by the principle of complementarity.

Gradually a protocell appears.

6. The whole factory surrounds itself by a lipid membrane and comes out of some porous mineral structure like clay.

7. A nuclei separates itself from the rest of the cell (in eukaryotes). The protein biosynthesis (ribosomes) moves out from the nuclei. Only DNA and RNA processing remain in the nuclei, where all kind of RNA are being processed, including mRNA (messenger RNA) or non-coding RNA (ribosomal, transfer, snoRNA and others).

8. A variety of proteins increases, the accuracy and speed of DNA copying grow, thanks to protein enzymes. A protein splicing appears…

9. Different organelles (parts of a cell) appear, which made of proteins. They specialize on their functions, taking part in the general process of replicator's copying. The main goal remains the same — the multiplication of replicators, more accurate and faster.

An epoch of cooperation and competition comes:

10. Unicellular organisms start eating each other, the first predators appear.

11. A symbiogenesis happens, that is a merging of big unicellular creatures with small ones: mitochondria and chloroplasts.

12. Simple multicellular organisms appear, which consist of identical or similar unicellular ones.

13. A cell specialization started by regulating of gene expression. The somatic cells are generated to form various tissues of a multicellular organism. They have a limit of their reproduction cycle, Hayflick limit. Gametes appear.

14. Species appear. Further read Darwin's «The origin of species».

Excuse me for I couldn't manage in a week of Creation, but two weeks are quite good, too.