The origins of life at our fingertips

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Monday, January 11, 2010

By Caitlin Hannah, UCSC science writing student

Biochemist David Deamer has been studying the origins of life for more than 20 years.

A spear of summer grass, like the gentle hand of a violinist, lifts and bows. Dew drops collect on its tip while all around it, life awakens to warm streams of sunlight. Below, an earthworm creeps its way through wet and crumbling earth. Birds awaken with trilling calls, while we prepare for our day in a civilized cacophony.

But wait a second.

How did we get here? How did that earthworm and those birds come to be? How did that spear of summer grass become as graceful as a trained violinist?

A few dozen curious scientists are tinkering with the laws of chemistry and physics to try to answer these questions, which boil down to one grand challenge:

How did life begin?

David Deamer, a professor of biochemistry at UC Santa Cruz, has pursued this challenge for more than 25 years. Deamer is a self-described synthetic biologist--a new breed of scientist who merges biology, chemistry, and engineering to try to create life forms from scratch. Like a paleontologist studying fossils, Deamer uses the methods of synthetic biology to unveil the story of life and evolution on Earth.

"We're using the laws of chemistry and physics to try to figure out, by reasoning backwards in time, what could have been even simpler than what we have today," says Deamer. "Life today is very complex."

While he spends much of his time applying these laws in his research, he has also become one of the first in his field to step away from the laboratory. In fact, he stepped so far that he found himself hovering over steaming, bubbling hot springs in Kamchatka, Russia; Mount Lassen, California; and Kilauea, Hawaii.

Deamer's research is based on the "Primordial Soup Theory," first proposed in 1924 by the Russian scientist Alexander Oparin. The theory has matured, but the basics remain the same: on Earth, organic compounds existing in a murky, primordial ooze joined together into increasingly complex molecules that somehow assembled into primitive living systems. Scientists now know that these organic compounds--amino acids, sugars, and hydrocarbons, among others--form both on our planet and in outer space. Proof of this came in 1969 when the primitive Murchison meteorite fell in Australia. The meteorite, and others like it, contained virtually all of the organic compounds that might be required for life to arise. Deamer's research goal is essentially to recreate the "Primordial Soup" and have it produce cells in the same way that it may have done billions of years ago.

Cells, the units of all life, have two essential properties: they grow and reproduce. To grow, cells take in energy and nutrients from the environment. To reproduce, they replicate and pass on genetic information when they divide.

The first thing a cell must do is develop an outer boundary: its membrane. The membrane must be strong enough to keep things in, yet porous enough to allow molecules to pass through so that the cell can consume what it needs.

Deamer has found that cell-like compartments form when certain molecules go through a wet-dry cycle, as they would on the border of a hot spring. When the molecules are wet, they're too dilute to undergo the chemical reactions needed for life. But when they're dry, they're more concentrated. Some molecules link together to create more complex structures resembling proteins and the nucleic acids that carry genetic information.

After several wet-dry cycles, systems of complex molecules emerge within the compartments. These "protocells" contain random combinations of molecules inside structures similar to a cell's membrane. The protocells aren't alive, but given enough time, it seems possible that some will contain just the right mix of molecules to begin to grow and replicate. That would mark the actual origin of life--and that is what Deamer and colleagues are trying to do in the lab.

So far, synthetic biologists have captured proteins that can spark reactions in the protocell, as well as nucleic acids. They can get energy and nutrients across the membrane so that the system can grow and even replicate genetic information. For instance, if DNA is in the protocell, it can be used to synthesize its sister genetic molecule RNA, which then can direct the protocell to make proteins. However, synthetic biologists don't yet know how RNA or DNA arose on the early Earth.

Once a viable cell does form, evolution takes over. Life begins to adapt to different environments. Some cells use light for energy, while others extract energy from minerals. Primitive cells, like today's bacteria, form mats on mineral surfaces that function together as cooperative systems. It took two billion years, but multicellular organisms emerged from this process--creating the network of life we see today.

"It's not too hard to understand the cooperative effect of evolution as well as the competitive," says Deamer. Evolution doesn't always involve one guy running faster than the other. In fact, evolution often favors groups that can work together to form a stronger unit.

While lab work continues, Deamer has started working on a new approach in volcanic settings. He and his colleagues choose these sites as models of what Earth would have been like four billion years ago.

One key problem that stands in the way of our understanding of how the first cells formed is that scientists don't know what Earth's environment was like as life arose. They can tinker away in labs, but the success of their work is only as good as their assumptions about this primitive setting. Although scientists know relatively little about the environment of early Earth, they do know that it was most likely volcanic when life first evolved.

This is why Deamer tries to visit different volcanic places. His goal is to see whether the results of lab experiments can be repeated under natural conditions like those on early Earth. In one such experiment, Deamer poured a mixture of amino acids and other biochemical compounds essential for life into a steaming pool of water near an active volcano in Kamchatka. And indeed, things did work differently than in the lab: No membrane-like structures appeared, protocells did not spontaneously arise, and there was no sign that the compounds assembled into chains resembling proteins or nucleic acids.

"We all sort of assume that things are going to happen just the way they do in the laboratory. And we discovered, no they don't," says Deamer. His colleagues, who have been working to get it right in the lab for years, find his explorations a bit unnerving. "They don't like that I'm challenging some of the things they've been assuming for many years as being real. But I'm saying that the laboratory is not necessarily the real world. There are some problems that you only discover when you try an experiment in a real-world setting. But then you also have a chance to discover a solution."

Creating life from scratch has proven extremely difficult--so difficult, in fact, that it may seem rare for life to arise elsewhere in the universe.

However, Deamer believes life is likely to be abundant. "If you go a few hundred light years away, you might expect to find planets like Earth that harbor simple life forms resembling bacteria," he maintains. There are thousands of stars within that distance--so it's likely that at least a few of them have what it takes to create life. "What we don't know is how likely it is for intelligence to appear. It could be just a lucky chance, but it could also be, given enough time, that life inevitably becomes intelligent. That's one of those huge questions we can't yet even begin to answer."

Perhaps we're the only ones preparing to work, or to play, every morning. Or perhaps that sound is echoed all across our universe: the cacophonous orchestra of life.

Caitlin Hannah, a senior majoring in Earth sciences and anthropology, wrote this article in spring 2009 for SCIC 160: Introduction to Science Writing.

 

 

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