Washington, Nov.23 : A research team led by the University of Colorado at Boulder and the University of Milan has discovered some unexpected forms of liquid crystals of ultra-short DNA molecules immersed in water, which could reveal information about the emergence of life on Earth.
CU-Boulder physics Professor Noel Clark said the team found that surprisingly short segments of DNA, life's molecular carrier of genetic information, could assemble into several distinct liquid crystal phases that "self-orient" parallel to one another and stack into columns when placed in a water solution.
Life is widely believed to have emerged as segments of DNA- or RNA-like molecules in a pre-biotic "soup" solution of ancient organic molecules.
"We found that even tiny fragments of double helix DNA can spontaneously self-assemble into columns that contain many molecules. Our vision is that from the collection of ancient molecules, short RNA pieces or some structurally related precursor emerged as the molecular fragments most capable of condensing into liquid crystal droplets, selectively developing into long molecules," Clark said.
Clark said scientists have been seeking effective ways for simple molecules to spontaneously self-select, "chain-up" and self-replicate.
According to him, the new study shows that in a mixture of tiny fragments of DNA, those molecules capable of forming liquid crystals selectively condense into droplets in which conditions are favourable for them to be chemically linked into longer molecules with enhanced liquid crystal-forming tendencies.
Liquid crystals -- organic materials related to soap that exhibit both solid and liquid properties -- are commonly used for information displays in computers, flat-panel televisions, cell phones, calculators and watches.
Most liquid crystal phase molecules are rod-shaped and have the ability to spontaneously form large domains of a common orientation, which makes them particularly sensitive to stimuli like changes in temperature or applied voltage.
The CU-Boulder and University of Milan team began a series of experiments to see how short the DNA segments could be and still show liquid crystal ordering, said Clark.
The team found that even a DNA segment as short as six bases, when paired with a complementary segment that together measured just two nanometers long and two nanometers in diameter, could still assemble itself into the liquid crystal phases, in spite of having almost no elongation in shape.
Structural analysis of the liquid crystal phases showed that they appeared because such short DNA duplex pairs were able to stick together "end-to-end," forming rod-shaped aggregates that could then behave like much longer segments of DNA.
The sticking was a result of small, oily patches found on the ends of the short DNA segments that help them adhere to each other in a reversible way -- much like magnetic buttons -- as they expelled water in between them, Clark said.
"The key observation with respect to early life is that this aggregation of nano DNA strands is possible only if they form duplexes," Clark said.
Apart from Clark, the other co-authors of the paper were Michi Nakata and Christopher Jones from CU-Boulder, Giuliano Zanchetta and Tommaso Bellini of the University of Milan, Brandon Chapman and Ronald Pindak of Brookhaven National Laboratory and Julie Cross of Argonne National Laboratory.
Nakata died in September 2006. (ANI)
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