MadSci Network: Science History

Re: What is the importance of Cech and Altman's work to understaning life?

Date: Tue May 25 17:02:28 2004
Posted By: Steve Mack, Post-doc/Fellow, Molecular and Cell Biology
Area of science: Science History
ID: 1081723509.Sh

Hi Malcolm,

Thanks for asking such a great question. I hope that this answer helps you understand how studying chemistry can teach us about the origins of all living organisms.

Sidney Altman and Thomas Cech received the 1989 Nobel Prize in Chemistry for their discoveries of the catalytic abilities of RNA. Prior to their discovery, biomolecules (the molecules found in the cell) were divided into a few distinct categories. Nucleic acids (DNA and RNA) were thought to be molecules of heredity, which served to only store genetic information (in the case of DNA) and direct the synthesis of new proteins (in the case of RNA), while proteins were thought to be the molecules of function, providing structure for the cell and carrying out the catalytic reactions (in the case of enzymes) necessary for metabolism, the synthesis of new proteins, and nucleic acid replication (among other tasks).

Given this viewpoint, it was not at all clear how modern organisms could have evolved from a simpler biological system, because proteins could not store the genetic information that directed their synthesis, and nucleic acids could not catalyze the reactions necessary to copy themselves (or any of the myriad other reactions that need to occur in a cell). Both types of molecules seemed to be absoloutely necessary for a living system.

Altman and Cech demonstrated that some RNA molecules could function as catalysts; that is to say that these RNA molecules could cause a reaction to occur without being changed by that reaction, just as enzymes (protein-based catalysts) do. Altman showed that the RNA-cutting activity of the RNAse P enzyme resided in the enzyme's RNA cofactor; one RNA molecule was catalyzing the clevage of another. Cech discovered a self-splicing RNA molecule. This is an RNA molecule which can cut itself (much as RNAse P cut another RNA molecule) and then re-connect the cut pieces, in a process known as splicing. In both cases, the reaction was carried out by RNA molecules and not by proteins. To distinguish these RNA-based catalysts from protein-based enzymes, the RNA catalysts are known as ribozymes.

The discovery of ribozymes changed the way in which biomolecules were categorized. Where RNA had previously been restricted to the category of heredity molecule, it is now seen as both a molecule of heredity and function. This in turn changed the viewpoint on the possible nature of a simpler biological system. It was possible that the roles played by DNA and protein in modern organisms could have been played by RNA alone in more primative organisms. This has given rise to theories of an ancient (billions of years ago) RNA world, in which the organisms were primarily RNA based, rather than DNA and protein based (as today).

So, while the Nobel Prize-winning work of Altman and Cech does not bear so much on the start of life on Earth so much as on the origins of modern DNA-protein based organisms, it has given those scientists who think about the start of life on Earth a molecule that can function both to store information and to catalyze chemical reactions, and these are two requirements of the first living organisms.

It might be a little advanced for you, but if you want to know more about this topic, I suggest taking a look at The RNA World, 2nd Edition (2001) by Raymond F. Gesteland (Editor), Thomas R. Cech, John F. Atkins. This should prove to be a thorough and up-to-date synopsis of the ideas that I've touched on here, and some of the introductory chapters might address your questions.

Keep asking questions!

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