The amazing ribosome

By Martín Bonfil Olivera
Published in Milenio Diario, October 14th, 2009

The chemistry Nobel prize thrilled me even more than the one for Medicine.

It was given to Venkatraman Ramakrishnan (Hindu, nationalized American, but living in Great Britain), Thomas Steitz (United States) and Ada Yonath (Israeli) because of "their studies about the structure and function of the ribosome".

If, like I mentioned last week, enzymes are amazing molecular machines that practically carry out all the functions of a living cell, ribosomes are an real automatized factories that manufacture, with absolute precision, each one of the thousands of different proteins we need to be alive.

A ribosome is a complex structure made of ribonucleic acid (the one-strand cousin of DNA) and many proteins.

It has some fixed parts, and other that move with robotic precision to assemble, in a matter of minutes, and from reading the information coming from DNA, proteins made up by thousands of amino acids, strung together as pearls in a necklace.

The achievement of the Nobel winners was to localize with great precision each one of the hundreds of thousands of atoms that form a ribosome, and this has allowed them to understand their functioning in atomic detail. They used X ray crystallography, a technique developed in the beginning of the 20^th century (and the same one that allowed Watson and Crick to discover the DNA double helix structure in 1953 --a structure, I might add, infinitely simpler than a ribosome).

To achieve this, they first had to obtain perfectly arranged crystals formed by pure ribosomes. It took them almost 20 years.

But to see atoms, one cannot use an optical microscope, not even an electron microscope. Only X rays have the necessary finesse. And no lens can focus them to form images: you have to gather the group of stains formed as the X rays travel through the crystals (originally the stains were captured on photographic film, but today they are captured by a couple charged device or CCD, the invention that this year won the Physics Nobel prize) and using computers to mathematically process data.

The result? Computerized models that reveal, with a very high level of detail, each screw and bolt of these wonderful molecular nano-factories.

As an additional benefit, these models are allowing scientist to develop new antibiotics that work like monkey wrenches tossed into the ribosomes of bacteria that make us sick.

Yes, I loved this year's chemistry Nobel. Too bad that Harry Noller, one of the giants of ribosome research, was left out of the prize, which can only be given to three persons.

(translated by Adrián Robles Benavides)

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The Nobel telomere

By Martín Bonfil Olivera
Published in Milenio Diario, October 7th, 2009

Nobel prizes are always exciting. This year's Physiology or Medicine prize reveals fascinating basic science about our cells which might have revolutionary applications in health.

It was awarded, according to the Nobel committee at the Karolinska Institute in Sweden, "for the discovery of how chromosomes are protected by telomeres and the enzyme telomerase", a discovery made by investigators Elizabeth Blackburn, her colleague Jack W. Szostak and her student Carol Greider.

The genetic information of living beings is written in the molecule of deoxyribonucleic acid, DNA, which form tangles called chromosomes within the nuclei on each of our cells.

Each chromosome is formed by a single, very long, DNA molecule. When it has to be copied, before the cell divides in two, the task is performed by an enzyme molecular machine made of protein.

Picture it like this: the famous DNA double helix is like a train railway. To copy it, both rails are separated and the enzyme slides over each one, reading the letters that form it and inserting the corresponding letters on the other side. Like a little train that advances in a rail, constructing the opposing rail. In the end, we have two complete and identical railways.

(http://www.youtube.com/watch?v=hfZ8o9D1tus)

But when the enzyme reaches the end of the rail, it cannot advance any longer, and does not construct the last span of the opposing rail. Each time that a chromosome is copied, their tips (telomeres, from the greek telos, end, and meros, part) would shorten!

Using a very ingenious experiment, Blackburn and Szostak discovered in 1982 that telomeres protect chromosomes so they are not destroyed. They constructed mini-chromosomes and added telomeres to some, but not all, of them. When they inserted the chromosomes inside cells, those with telomeres survived, but the ones that didn't have them were rapidly eliminated.

And in 1984 (Christmas day!), Blackburn and Greider discovered another enzyme that allows telomeres to maintain their size. It achieves it because it has a mold with the correct letter sequence (CCCCAA) that have to be inserted in each tip of DNA. They named it "telomerase" (the termination "ase" in biochemistry indicated an enzyme).

Today we know that telomeres and telomerase play a role in aging and cellular death (when telomeres are shortened) and influence the uncontrolled multiplication of cancerous cells (because their telomerase is very active and their telomeres are not shortened). There are even vaccines in development to try to fight cancer by inactivating the telomerase of tumors.

Basic science, motivated by simple curiosity, offers a new medical promise, although a far one.

(translated by Adrián Robles Benavides)

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