Происхождение жизни / The Origin of Life: Происхождение жизни

The Origin of Life
Author: Stanislav Mitichkin (Russia, 2010)

staswiz 29.08.12 в 09:47

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.

staswiz 29.08.12 в 09:49

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

staswiz 29.08.12 в 09:57

It appeared very simply, 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 nearby volcanoes. The Earth goes round the Sun and spins round its own axis, so there are days and nights. It's enough.

staswiz 29.08.12 в 10:02

And now a miracle happens.

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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 free nucleotides as bricks. They connect together by weak hydrogen bonds according to the principle of complementarity.

staswiz 29.08.12 в 10:14

A day is dawning, the Sun is warming the water up to ~80 degrees Celsius (it's a hot spring, right?) and hydrogen bonds are broken. Now we have two separate but complementary chains. The Sun is shinning with ultraviolet radiation and the chains are growing with 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 bricks, in the day they separate. Connecting the bricks at nights, separating at days. We have a REPLICATION by natural way.

staswiz 29.08.12 в 10:22

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

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At night it creates a complementary chain:
AGUC
UCAG

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At day the water warms, the hydrogen bonds broke and it divides into two chains: AGUC and UCAG.

staswiz 29.08.12 в 11:00

Next night it again creates a complementary chain, but now two of them:
AGUC
UCAG
and
UCAG
AGUC.

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

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And a replication started...

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2. Then ribozymes appear.

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Now the chain becomes longer and starts to join itself by complementary bonds. One tail of the chain joins another. Or the second quarter joins the third quarter. In result we have a secondary structure of the molecule, which folds in a definite way and has a catalytic ability. It accelerates its own replication (or the replication of its unfolded neighbours).

staswiz 29.08.12 в 11:28

How really it was in detail maybe no one would learn. Let's 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 approach them later.

staswiz 29.08.12 в 12:12

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

staswiz 29.08.12 в 12:22

3. Mutations and the natural selection. We already have an ancient camera/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 they survive who can replicate and do it FASTER. It means they have a more perfect catalytic ability of their own replication.

staswiz 29.08.12 в 12:28

4. Now let's assume one of "error" replicator's copies gained an ability to cut itself (self-splicing). There is no any fantastic here. It is proven that some RNA molecules can cut itself. Tested in vitro.

staswiz 29.08.12 в 12:38

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 the 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.

staswiz 29.08.12 в 12:48

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

staswiz 29.08.12 в 12:53

* 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.

staswiz 29.08.12 в 13:09

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

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

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

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

staswiz 29.08.12 в 13:29

Then DNA appeared as a reliable storage of information.

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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.

staswiz 29.08.12 в 13:45

Gradually a protocell appears.

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

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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).

staswiz 29.08.12 в 13:50

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

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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.

staswiz 29.08.12 в 14:09

An epoch of cooperation and competition comes:

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

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

staswiz 29.08.12 в 14:21

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

staswiz 29.08.12 в 14:23

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.

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

staswiz 29.08.12 в 14:39

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

staswiz 29.08.12 в 14:40