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Hot Topic Origins Origin & Evolution of Life Linking Life's Elements
 
Linking Life's Elements
Based on an American Society for Biochemistry and Molecular Biology news release
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Origin & Evolution of Life
Posted:   01/03/09

Summary: Researchers have unlocked new clues about how ancient organic molecules may have first combined to form biologically useful strands of RNA. This single-stranded precursor to DNA is essential for living cells, and some scientists believe the first life on Earth may have been RNA-based rather than DNA-based.

Linking Life's Elements

A simple fusion to jump-start evolution

With the aid of a straightforward experiment, researchers have provided some clues to one of biology's most complex questions: how ancient organic molecules came together to form the basis of life.

DNA double-helix structure
Like DNA, the single-helix structure of RNA resembles a spiral staircase.
Credit: Darryl Leja/Access Excellence.

Specifically, this study, which appeared online in the Journal of Biological Chemistry, demonstrated how ancient RNA joined together to reach a biologically relevant length.

RNA, the single-stranded precursor to DNA, normally expands one nucleic base at a time, growing sequentially like a linked chain. The problem is that in the primordial world RNA molecules didn't have enzymes to catalyze this reaction, and while RNA growth can proceed naturally, the rate would be so slow the RNA could never get more than a few pieces long (for as nucleic bases attach to one end, they can also drop off the other).

Ernesto Di Mauro and colleagues examined if there was some mechanism to overcome this thermodynamic barrier, by incubating short RNA fragments in water of different temperatures and pH.

The earliest life may have used RNA for functions now fulfilled by DNA and proteins.

They found that under favorable conditions (acidic environment and temperature lower than 70 C), pieces ranging from 10-24 in length could naturally fuse into larger fragments, generally within 14 hours.

The RNA fragments came together as double-stranded structures then joined at the ends. The fragments did not have to be the same size, but the efficiency of the reactions was dependent on fragment size (larger is better, though efficiency drops again after reaching around 100) and the similarity of the fragment sequences.

The researchers note that this spontaneous fusing, or ligation, would a simple way for RNA to overcome initial barriers to growth and reach a biologically important size; at around 100 bases long, RNA molecules can begin to fold into functional, 3D shapes.

 

 

 


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