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Scientists have made artificial genetic molecules called XNA that are similar to DNA. DNA,illustrated here, is a pair of long, intertwined chains made of repeating chemical building blocks.

Credit: Frank Ramspott/iStockphoto

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DNA, RNAand XNA?

By Roberta Kwok / May 7, 2012

Insideyourbodyscells,

molecules called DNA act as instruction booklets. DNA tells the cells within every living thing whichmolecules to make. Everything about you your hair color, height, voice is determined at leastpartly by your DNA.

DNA and its partner molecule, RNA, are the only molecules in nature known to carry geneticinformation. Now, in a new study, scientists have created artificial molecules that also store geneticinstructions. These new molecules called XNA are similar to DNA and RNA but slightlytweaked.

DNA is a air of lon , intertwined chains made of re eatin chemical buildin blocks. Each buildin

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block contains three parts: a sugar called deoxyribose, a phosphate molecule and a moleculecalled a base. There are four bases in DNA: adenine, thymine, guanine and cytosine, or A, T, G, Cfor short. The bases are like the letters in the instruction manual.

Cells read the DNA and make a molecule called RNA. RNA is made of similar repeating units, butit has a different type of sugar, called ribose, in each building block. The cell then reads the RNA tocreate molecules called proteins, which perform important functions in the body.

XNA is similar to DNA and RNA. But the researchers made an important change: They didnt usethe sugars in DNA and RNA. Instead, they substituted different molecules. The team created sixtypes of XNA, each with a different molecule in the spot where a deoxyribose or ribose would be inDNA and RNA.

What makes DNA and RNA so cool is they are the genetic molecules, they are the basis forpropagating information through generations, Gerald Joyce told Science News. Joyce is abiochemist, someone who studies the chemistry of living things, at the Scripps Research Institute inLa Jolla, Calif. Well, now we have eight genetic molecules: RNA, DNA and these six.

For genetic information to be useful, the cell needs a way to copy it. When a cell divides, it passes

on one copy of its genetic information to each daughter cell.

To create a copy machine, the scientists made molecules called enzymes that could read theXNA. The enzymes built molecules of DNA that contained the same information as the XNA. Theprocess is similar to translating a story from English to French. The words may look different, but theunderlying information is the same.

The enzymes could also translate the DNA back into XNA. So the scientists had a way to makecopies of XNA molecules.

Finally, the team wanted to find out if the XNA could evolve. Evolution is the process of changing

genetic information over generations. DNA evolves when individual letters are tweaked, slightlyaltering the instruction manual.

The scientists gave XNA a simple evolution test. They mixed XNA with other molecules and pickedthe XNAs that were the best at attaching to those molecules. Then the researchers copied thoseXNAs and repeated the process of mixing them with other molecules several times. The XNAs gotbetter and better at attaching to the molecules. They were evolving.

The new study hints that forms of life based on molecules other than DNA and RNA might bepossible. We only know this one example of life its whats been on Earth for 4 billion years,Joyce told Science News. But perhaps there are organisms on other planets that have different

types of genetic molecules than we do.

Power Words

DNA The genetic instructions inside cells that tell them which molecules to make.

RNA An intermediate molecule in the process of reading DNA to create proteins in the cell. Acells molecular machinery reads DNA to create RNA, then reads RNA to create proteins.

evolve To change gradually over generations.