New Way To Think About Earth's First Cells
ScienceDaily (Jun. 6, 2008) - A team of researchers at Harvard University 
have modeled in the laboratory a primitive cell, or protocell, that is 
capable of building, copying and containing DNA.
Since there are no physical records of what the first primitive cells on 
Earth looked like, or how they grew and divided, the research team's 
protocell project offers a useful way to learn about how Earth's earliest 
cells may have interacted with their environment approximately 3.5 billion 
years ago.
The protocell's fatty acid membrane allows chemical compounds, including the 
building blocks of DNA, to enter into the cell without the assistance of the 
protein channels and pumps required by today's highly developed cell 
membranes. Also unlike modern cells, the protocell does not use enzymes for 
copying its DNA.
Led by Jack W. Szostak of the Harvard Medical School, the research team 
published its findings in the June 4, 2008, edition of the journal Nature's 
advance online publication.
"Szostak's group took a creative approach to this research challenge and 
made a significant contribution to our understanding of small molecule 
transport through membranes," said Luis Echegoyen, director of the NSF 
Division of Chemistry.
Some scientists have proposed that ancient hydrothermal vents may have been 
sites where prebiotic molecules--molecules made before the origin of life, 
such as fatty acids and amino acids--were formed.
When fatty acids are in an aqueous environment, they spontaneously arrange 
so that their hydrophilic, or water-loving, "heads" interact with the 
surrounding water molecules and their hydrophobic, or water-fearing, "tails" 
are shielded from the water, resulting in the formation of tiny spheres of 
fatty acids called micelles.
Depending upon chemical concentrations and the pH of their environment, 
micelles can convert into layered membrane sheets or enclosed vesicles. 
Researchers commonly use vesicles to model the cellular membranes of 
protocells.
When the team started its work, the researchers were not sure that the 
building blocks required for copying the protocell's genetic material would 
be able to enter the cell.
"By showing that this can happen, and indeed happen quite efficiently, we 
have come a little closer to our goal of making a functional protocell that, 
in the right environment, is able to grow and divide on its own," said 
Szostak.
"We have found that membranes made from fatty acids and related molecules --  
the most likely components of primitive cell membranes -- have properties 
very different from those of the modern cell membrane, which uses 
specialized pumps, channels or pores to control what gets in and out," says 
Jack Szostak, PhD, of the MGH Department of Molecular Biology and Center for 
Computational and Integrative Biology, the report's senior author. "Our 
report shows that very primitive cells may have absorbed nutrients from 
their environment, rather than having to manufacture needed materials 
internally, which supports one of two competing theories about fundamental 
properties of these cells."
Szostak's team carefully analyzed vesicles comprised of different fatty acid 
molecules and identified particular features that made membranes more or 
less permeable to potential nutrient molecules. They found that, while large 
molecules such as strands of DNA or RNA could not pass through fatty acid 
membranes, the simple sugar molecules and individual nucleotides that make 
up larger nucleic acids easily crossed the membrane.
To further explore the function of a fatty acid cell membrane, the 
researchers used activated nucleotides they developed for this study that 
will copy a DNA template strand without needing the polymerase enzyme 
usually required for DNA replication. After placing template molecules 
inside fatty-acid vesicles and adding the activated nucleotides to the 
external environment, they found that additional DNA was formed within the 
vesicles, confirming that the nucleotide molecules were passing through the 
fatty-acid membranes.
Co-authors of the Nature paper include Sheref S. Mansy, Jason P. Schrum, 
Mathangi Krishnamurthy, Sylvia Tobe and Douglas A. Treco of the Szostak 
Laboratory.
The research was supported with funding from the National Science Foundation 
(Division of Chemistry award number 0434507). Jack W. Szostak was also 
supported by National Aeronautics and Space Administration Exobiology 
Program award number EXB02-0031-0018.  Sheref S. Mansy was supported by 
National Institutes of Health award number F32 GM07450601.
Adapted from materials provided by National Science Foundation.
National Science Foundation (2008, June 6). New Way To Think About Earth's 
First Cells. ScienceDaily. Retrieved June 6, 2008, from 
http://www.sciencedaily.com­
Rayilyn Brown
Board Member AZNPF
Arizona Chapter National Parkinson's Foundation
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