"Long before it's in the papers"
January 27, 2015


Scientists said to get DNA-like molecule to assemble itself

Dec. 23, 2013
Courtesy of Georgia Tech
and World Science staff

Chemists say they have found a way to make a DNA-like mol­e­cule as­sem­ble it­self in a pond-like set­ting—po­ten­tially sug­gest­ing a key step in how life orig­i­nat­ed. 

The re­search­ers ac­tu­ally worked with a sim­pler mol­e­cule, called pre-RNA. It’s hy­poth­e­sized to have even­tu­ally evolved in­to DNA—one stop­ping point along the way hav­ing been the crea­t­ion of a third sub­stance, RNA, still used in the body to trans­late the code in­scribed in DNA.

Sci­en­tists had long strug­gled to show how even pre-RNA, the eas­i­est to build of the three mol­e­cules, might have self-as­sem­bled. To­day they don’t need to—they are cop­ied us­ing pre-existing cel­lu­lar machin­ery—but the first ones pre­sumably had no such help.

The study dem­on­strat­ed a chem­i­cal re­ac­tion “that we see as im­por­tant for the forma­t­ion of the ear­li­est RNA-like mol­e­cules,” said one of the re­search­ers, bio­chem­ist Nich­o­las Hud, who di­rects the Cen­ter for Chem­i­cal Ev­o­lu­tion at the Geor­gia In­sti­tute of Tech­nol­o­gy. The study was pub­lished Dec. 14 on­line in the Jour­nal of the Amer­i­can Chem­i­cal So­ci­e­ty. 

RNA or pre-RNA con­sist of three chem­i­cals. Two are ri­bose and phos­phate. The third is called a base, but there are a few pos­si­ble bas­es. The three com­po­nents, in any event, link to­geth­er to form just one un­it of the mol­e­cule. The whole mol­e­cule con­sists of many of these un­its. This al­lows it to store in­forma­t­ion, em­bed­ded in the spe­cif­ic se­quence of bas­es. DNA is si­m­i­lar to the oth­er two mol­e­cules, though it’s double-stranded, like a lad­der—good for its sta­bil­ity—whereas the oth­er mol­e­cules are single-stranded, like lad­ders cut down the mid­dle.

Hud’s team in­ves­t­i­gated bas­es chem­ic­ally re­lat­ed to those of mod­ern RNA, but that might be able to spon­ta­ne­ously bond with ri­bose and as­sem­ble with oth­er bas­es. They fo­cused on a mol­e­cule called tri­am­in­opy­rim­i­dine, or TAP, which they mixed with ri­bose un­der con­di­tions meant to mim­ic a dry­ing pond on early Earth. 

TAP and ri­bose re­acted to­geth­er with up to 80 per­cent of TAP be­ing con­vert­ed in­to nu­cle­o­sides, the un­its of RNA, the sci­en­tists re­ported. “This study is im­por­tant in show­ing a fea­si­ble step for how we get the start of an RNA-like mol­e­cule,” and al­so how the build­ing blocks “could have found each oth­er and self-as­sem­bled in what would have been a very com­plex mix­ture of chem­i­cals,” Hud said.

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Chemists say they have found a way to make a DNA-like molecule assemble itself in a pond-like setting—potentially suggesting ways life might have originated. The researchers actually worked with a simpler molecule, called pre-RNA. It’s hypothesized to have eventually evolved into DNA—one stopping point along the way having been the creation of a third substance, RNA, still used in the body to translate the code inscribed in DNA. Scientists had long struggled to show how even pre-RNA, the easiest to build of the three molecules, might have self-assembled. Today they don’t need to—they are copied using pre-existing cellular machinery—but the first ones presumably had no such help. The study demonstrated a chemical reaction “that we see as important for the formation of the earliest RNA-like molecules,” said one of the researchers, biochemist Nicholas Hud, who directs the Center for Chemical Evolution at the Georgia Institute of Technology. The study was published Dec. 14 online in the Journal of the American Chemical Society. RNA or pre-RNA consist of three chemicals. Two are ribose and phosphate. The third is called a base, but there are a few possible bases. The three components, in any event, link together to form just one unit of the molecule. The whole molecule consists of many of these units. This allows it to store information, embedded in the specific sequence of bases. DNA is similar to the other two molecules, though it’s double-stranded, like a ladder—increasing its stability—whereas the other molecules are single-stranded, like ladders cut down the middle. Hud’s team investigated bases chemically related to those of modern RNA, but that might be able to spontaneously bond with ribose and assemble with other bases. They focused on a molecule called triaminopyrimidine, or TAP, which they mixed with ribose under conditions meant to mimic a drying pond on early Earth. TAP and ribose reacted together with up to 80 percent of TAP being converted into nucleosides, the units of RNA, the scientists reported. “This study is important in showing a feasible step for how we get the start of an RNA-like molecule, but also how the building blocks of the first RNA-like polymers could have found each other and self-assembled in what would have been a very complex mixture of chemicals,” Hud said.