Cienciaes.com: The thousand and one bases of DNA.

2021-02-11 13:42:41

Today, in the podcast, I am going to tell you a story. A story that gave rise to the title of my first popular science book that I published, in the Hélice publishing house, and which, like the story was titled: the thousand and one bases of ADN and other scientific essays. With this story he tried to explain the idea behind one of the first technologies for sequencing ADN, invented by the scientist Frederic Sanger, and which earned him his second Nobel Prize in Chemistry, in 1980. The first had been received in 1958 for his contribution to determining the amino acid sequence of proteins. Sanger was undoubtedly fascinated by the sequence of components of the most important molecules of life. His method was used to obtain the sequence of the first human genome, which was published in the year 2000.

He ADN It is made up of four small molecules (called bases of the ADN) attached to each other forming two long chains, coiled one over the other forming a double helix. These four small molecules, called adenine, thymine, cytosine, and guanine, are represented by the letters A,T,G, and C, and have the property that the A of one chain binds only to the T of the other, and the C through G. Thus, a string of sequences ACTGGG is attached to another sequence TGACCC. For this reason, it is said that the two chains of ADN They have complementary sequences. Knowing the sequence of one of the chains immediately knows that of the other. Moreover, this complementarity is the secret of the molecular reproduction of the ADN, since, from the sequence of one chain, the cell (and also a scientist in a tube) can make the other. Each chain thus serves as a template to manufacture another chain equal to its complement, and a molecule of ADN In this way, we have two.

So far, all good. But how do we find out the sequence of As, Tes, Ces, and Ges? I invite you to listen, in the podcast, to the tale of Princess Abdiena (also you can read the full text here )

The story explains the principle of the method that the scientist Fredecick Sanger and his team invented and which earned them the Nobel Prize. Taking advantage of the capacity of ADN to copy himself, they made fragments from an initial point that end in a certain letter, for example, A, and they measure their length with a simple method. They do this with the four letters, so they can know where they are from the starting point, thus achieving the complete sequence of letters. In this way, and using this method with many fragments of ADN different from the human genome, scientists have been able to obtain the sequence of its billions of letters. A herculean job.

That was the thing with respect to the sequencing technology of the ADN in the 1990s to 2000s. Since then, new generation technologies have made it possible to sequence entire genomes in just over a day. The technical details are complicated, but the idea is similar to copying a book of hundreds of pages in an hour. How can we do it? Well, one person alone couldn’t, but if we give a copy of that book to thousands and thousands of people and tell each one to choose a sentence at random and copy the end of the sentence that precedes it, the chosen sentence, and the beginning of the sentence that follows it, we will have in a few minutes thousands and thousands of copied sentences that in fact can mean, all together, several copies of the book. If these sentences are analyzed in a computer with the appropriate algorithm, they can be arranged in the same order in which they appear in the book simply by matching the endings and beginnings of the sentences that flank the complete sentences.

Something like this is done with the human genome and other species. Copies are first made and then cut into thousands and thousands of little pieces that are read at the same time. The order of the letters is extracted from that information by analyzing it by computer. Today we have the technology to sequence and analyze genomes at literally astronomical speeds. I have spoken about this on several occasions in previous Quilo programs. The development of artificial intelligence and new algorithms will make it possible, I believe, to extract information that is still hidden in the genomes of the species that will allow us to improve our understanding of how they work and why they are the way they are in each of them.

References:

The thousand and one bases of ADN

Works by Jorge Laborda.

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