Chemists fine-tune ideas on how life evolved

By Carol Clark

An iPod can store a music library in a wafer-thin device that fits in your palm, providing a vast amount of data at your fingertips. But a human cell, only a few microns across, contains all of the information that made you. And even more remarkable, the first complex cells are thought to have somehow self-assembled from the fundamental building blocks of life.

The Accounts of Chemical Research (ACR) devoted its entire December issue to ideas about this self-assembly process, and how it could have enabled life to emerge from the chemical soup of early Earth and grow increasingly complex. By understanding this process, chemists hope to boost our ability to bioengineer living systems in ways that benefit us, just as computer engineers do with digital devices like iPods.

“Chemists have spent a long time breaking down cells and looking at their individual components,” says Emory chemist Anil Mehta. “Now we have a fantastic understanding of these parts. So how do we put them together? How can we, as chemists, get new complex networks to emerge from these components that communicate with each other? We are right on the verge of achieving this.”

The special ACS issue was edited by three Emory chemists – Mehta, Jay Goodwin and David Lynn, who are all also part of the NSF/NASA Center for Chemical Evolution – and a University of Utah chemist, Cynthia Burrows.

“We’re trying to figure out how to get from inanimate matter to living matter,” Goodwin says. “It’s one of science’s greatest challenges, and a problem the scientific community has been working on for centuries.”

The quest has heated up during the last decade, largely driven by genetic sequencing technology and our growing understanding of the minimum amount of information needed for evolution.

Fossils from Western Australia indicate that the earliest life may have been primitive bacteria going back about 3.4 billion years. “But it wasn’t until the ribosome appeared, around 3 billion years ago, that life exploded,” Mehta says. “Everything seems to have radiated from the ribosome.”

Ribosomes are essentially little machines that churn out proteins from nucleic acids. And proteins and nucleic acids are two biological macromolecules that learned to collaborate in encoding, transmitting and expressing genetic information.

In a paper included in the ACR issue, the Emory chemists use a digital-to-analog converter model to explain how the polymer cooperation of ribosomes may have helped the first dynamic functional networks reach the critical threshold for the emergence of cellular life.

Presumably, the polymers of proteins and nucleic acids evolved separately, and then found a way to join forces. “They both have strengths and weaknesses,” Goodwin says. “And together they make a system that takes advantage of the strengths of both, generating greater diversity and evolutionary potential.”

The nucleic acids are the digital part of the system, providing the ability to store vast amounts of information, like songs on an iPod, with crucial and exacting accuracy. Proteins are analog, delivering responsiveness and a continually variable range of functionality, such as the ability to communicate with internal and external networks, or play the songs. The ribosome functions like a digital-analog convertor that joins these two components into a single, dynamic system.

“We recognize that the march of molecular history likely had many pathways,” Lynn says. The aim of the special ACR issue is to bring together different areas of research on the problem, he adds. “Just as it takes a diversity in chemical composition for the evolution of life, it takes a diversity of ideas to fully comprehend the origins of that evolution.”

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Top image: iStockphoto.com.