But new studies show RNA actually controls key actions by turning genes on and off, directing embryo development and, perhaps, playing a role in cancer.
This new understanding, found through a series of laboratory discoveries, has been named the No. 1 scientific breakthrough of the year by the journal Science, one of the world's top research magazines.
The magazine, in an article to appear in Friday's edition, also named nine other breakthroughs as runners-up. These range from discoveries about the mysterious elemental particle called the neutrino, to studies of the cosmic echo of the Big Bang, to a new fossil from an ancestor of the most complex of creatures, modern humans.
The role of RNA, which stands for ribonucleic acid, has long been thought to be a sort of drone for DNA, which holds the cell's genetic instructions. Some forms of RNA collect the DNA commands and deliver them to the cell's protein workshop where other RNA follows the instructions in assembling amino acids into proteins.
But new discoveries show that RNA can actually take charge of the genetic process, commanding genes to turn on or off, or even delete entire sections DNA.
RNA can be particularly powerful during cell division, helping it to go smoothly and unclogging the machinery when bits of DNA move into the wrong position. Disruptions of the RNA's work could play a role in cancer.
Some researchers are examining this new role of RNA in hopes it can be enlisted in the war against cancer and other diseases.
Following is a look at the other breakthroughs.
Researchers are finally learning more about one of the least understood of the elemental particles. Recent studies have shown that neutrinos have mass, long a debated point. Studies also have solved a puzzle about the flow of neutrinos from the sun's nuclear furnace. Physicists calculated that the sun should produce a certain number of electron neutrinos, one of the three types of the particle. But measurements of neutrino flow detected only a third of the expected number. Using new instruments, researchers determined that some electron neutrinos flowing from the sun changed into mu and tau neutrinos. When these were counted, the correct number of neutrinos were detected.
With increasing skill and more precise equipment, researchers are rapidly sequencing the genes for dozens of life forms. Since the human genome was sequenced in 2000, gene sequencing has been completed on the malaria parasite and the mosquito that spreads it. Also complete are the sea squirt, two types of rice, the mouse, the rat and dozens of types of microbes. Gene sequencing projects planned or under way include the chimpanzee, corn, the honey bee, dog, cow, chicken and sea urchin.
Some 400,000 years after the Big Bang, the theoretical beginning of the universe, nuclei and electrons cooled enough to form atoms. This spawned high energy radiation that even now exists as a faint glow called the cosmic microwave background, or CMB. Studying this radiation has given new insights about the nature of the infant universe and about its future. CMB studies suggest the universe will expand forever instead of collapse back on itself in a "Big Crunch" as some earlier research had suggested.
Physicists, using laser light, are now able to take pictures in times measured in attoseconds - billionths of a billionth of a second. They are using this skill to study the inner workings of the atom, a realm previously unseen.
Researchers have found proteins in the mouth and skin cells that cause spicy foods to taste hot and breath mints to taste cool. The proteins respond to both chemical flavors and to temperatures.
Using electron microscopes, scientists can now make three-dimensional pictures of the molecular structure of single proteins at work inside a cell. This should give unprecedented views of the how cells function, knowledge that could lead eventually to new medical treatments.
A new type of telescope is giving astronomers the clearest picture of the heavens yet from ground-based instruments. Telescopes on the ground must look through a constantly changing atmosphere which causes stars to twinkle and drop in and out of focus. A new technique, called adaptive optics, uses thousands of small, thin mirrors that are flexed hundreds of times each second by a computer to keep images in the distant universe in constant focus. The mirrors are warped slightly to compensate for the distortion caused by the atmosphere.
Science has known for years that light entering the eye helps to set the body's clock, guiding the sleep-awake cycle. Researchers this year found a new class of cells in the eye's retina that are not part of the vision system. Instead, these cells, called retinal ganglion cells, send signals to the brain to set the body's clock.
A fossil discovery in Africa pushed the date of the earliest known human ancestor back by more than 3 million years. Previously a 3.2-million-year-old fossil called Lucy, unearthed in East Africa, held the record. This year, researchers found a nearly complete skull on the shores of Lake Chad in western Africa and dated it at between 6 million and 7 million years old. The skull has some ape-like features, but the shape of the teeth and lower face suggests it is a human ancestor. It was nicknamed Toumai, which means "hope of life" in the Goran language of Africa.
By Paul Recer