When a cell divides, it passes on genetic information by producing copies of its DNA. Chemists have also learned to copy DNA. In the journal Angewandte Chemie, a German team has now introduced a new copying technique that uses a single strand of DNA as the “master copy”, like a cell, but does not require enzymes. Unlike earlier methods, it allows for stepwise growth of the chain in both the direction preferred by nature and the opposite direction typical of current DNA synthesis techniques.
Within a cell, the DNA double strand is separated in segments during the copying process. One of the single strands serves as the “master copy” or template. Polymerase enzymes snap together the corresponding nucleotides stepwise to form the new complementary strand, beginning with a “starting segment” known as a primer. The backbone of a DNA strand is an alternating chain of five-membered sugar rings and phosphate groups. The chain links are formed at the 3’ and 5’ oxygen atoms of the sugars; natural growth occurs in the 3’ direction.
One question relating to the origin of life is: How was nature able to copy DNA or RNA strands before polymerases existed? Since the 1980s, DNA synthesizers have allowed chemists to produce DNA strands, but without a template or primer; the sequence is determined by the order of addition of the reagents.
Only the use of protective groups that inhibit uncontrolled reactions and the programmed addition of the reagents ensure that the sequence of bases is correct. This is clearly not how nature does it. But how could template-directed primer extension function purely chemically, with no enzymes?
More recently, different approaches have been used to develop a method called chemical primer extension, which involves the reaction of activated nucleotides with the end of a slightly modified DNA primer. Clemens Richert, Andreas Kaiser, and Sebastian Spies of the University of Stuttgart (Germany) have now developed this method further.
They found a protective group that can be removed under gentle conditions so that the DNA duplexes made from the primer and template do not fall apart. This allows the reactivity of the nucleotides and the terminus of the primer to be switched on and off as desired, and the sequence information in the template strand can be read out nucleotide by nucleotide. For this method to work, the template and primer are both attached to tiny spheres. As in an automated synthesizer, the reagents and building blocks can flow over the spheres.
The primer is bound to the template through base pairing. A suitable nucleotide from the surrounding solution docks at the next vacant binding site of the template. The nucleotide then binds to the reactive end of the primer through activated phosphate units. The sites that are supposed to react are chemically altered to become more reactive than in natural DNA. The special thing about this method is that the chain extension can be controlled to occur in either the 3’ or the 5’ direction. This is not known to take place in nature.
So far, this process has remained quite slow and is limited to short sequences. Improvement should be possible through optimization of the reaction conditions and better automation.About the Author
Multi-institutional collaboration uncovers how molecular machines assemble
02.12.2016 | Salk Institute
Fertilized egg cells trigger and monitor loss of sperm’s epigenetic memory
02.12.2016 | IMBA - Institut für Molekulare Biotechnologie der Österreichischen Akademie der Wissenschaften GmbH
A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.
Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...
In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.
“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...
The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.
The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...
Broadband rotational spectroscopy unravels structural reshaping of isolated molecules in the gas phase to accommodate water
In two recent publications in the Journal of Chemical Physics and in the Journal of Physical Chemistry Letters, researchers around Melanie Schnell from the Max...
The efficiency of power electronic systems is not solely dependent on electrical efficiency but also on weight, for example, in mobile systems. When the weight of relevant components and devices in airplanes, for instance, is reduced, fuel savings can be achieved and correspondingly greenhouse gas emissions decreased. New materials and components based on gallium nitride (GaN) can help to reduce weight and increase the efficiency. With these new materials, power electronic switches can be operated at higher switching frequency, resulting in higher power density and lower material costs.
Researchers at the Fraunhofer Institute for Solar Energy Systems ISE together with partners have investigated how these materials can be used to make power...
16.11.2016 | Event News
01.11.2016 | Event News
14.10.2016 | Event News
02.12.2016 | Medical Engineering
02.12.2016 | Agricultural and Forestry Science
02.12.2016 | Physics and Astronomy