Previous studies typically have used biochemical techniques rather than lasers, which can directly grab and tug the RNA. Biochemical techniques give less clear estimates of how molecules fold in real time. They often give a description of the molecule's average folding behavior, which must be interpreted by mathematical models. Crystallography-a technique involving freezing the molecule in place-provides a good picture of its shape, but not how it forms or the energy involved.
"What we're interested in is understanding, in a very fundamental way, how biomolecules take the shapes they do, and how they perform the functions they do," Block said. "No one has been able to explore in great detail tertiary structure yet." RNA riboswitches must have this tertiary structure to work.
"Most RNAs just make secondary [two-dimensional] structure. But the ones that really do stuff," he added, "those all have tertiary structure."
What RNA can do
RNA has the job of copying the genetic code from DNA (transcription), and using that code to build the proteins organisms need to live (translation). To make RNA, a protein called RNA polymerase moves along the length of a strand of DNA. It reads a pattern in the building blocks of DNA, nucleic acids whose names are abbreviated A, C, G and T, and it makes RNA with a complementary pattern. This long strand of RNA is then the recipe for a specific protein. Another structure called a "ribosome," which is also made of RNA, then reads this recipe and makes a protein to order.
The RNA copied from DNA generally does not twist up very much, often only forming two-dimensional loops or tight bends called "hairpins." Occasionally, its loops and hairpins form a three-dimensional structure that does
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