Investigating the origin of life has intrigued researchers for centuries. To explain how life originated on Earth requires explaining how organic molecules essential to life — such as amino acids and nucleotides — were created and how these became larger molecules, including proteins and nucleic acids. After years of hard work, NASA scientists have recently synthesized several of the essential building blocks of life, creating three key structures found in RNA and DNA. DNA stores information for protein synthesis and RNA carries out the instructions encoded in DNA.
NASA scientists Michel Nuevo, Christopher Materese and Scott Sandford showed that the laboratory process of exposing an ice sample containing pyrimidine to ultraviolet radiation and simulating conditions in space produces these fundamental ingredients important in protein synthesis and many other functions. Pyrimidine is a ring-shaped molecule of carbon and nitrogen. It is the main structure for uracil, cytosine and thymine, parts of our genetic code. Pyrimidine is also seen in meteorites, yet researchers still are unsure of its origin.
Sandford states, “Our experiments suggest that once the Earth formed, many of the building blocks of life were likely present from the beginning. Since we are simulating universal astrophysical conditions, the same is likely wherever planets are formed.”
The scientists theorized that if molecules of pyrimidine were able to survive long enough to migrate into interstellar dust clouds, they might be able to protect themselves from destruction by radiation. To test out their hypothesis, the researchers placed the ice sample containing pyrimidine in space-like conditions, including an extremely high vacuum, very low temperatures of approximately -440 degrees Fahrenheit and harsh ultraviolet radiation.
They discovered in the laboratory that when pyrimidine is frozen in ice containing water with ammonia, methanol or methane, it is much less vulnerable to destruction by radiation than if it were simply in the gas phase in open space. Rather than being disintegrated, many of the molecules took on the new forms of uracil, cytosine and thymine.
Matarese comments, “We are trying to address the mechanisms in space that are forming these molecules. Considering what we produced in the laboratory, the chemistry of ice exposed to ultraviolet radiation may be an important linking step between what goes on in space and what fell to Earth early in its development.”
In November 2014, researchers at the W.M. Keck Laboratory at the University of Hawaii at Manoa demonstrated compelling evidence that glycerol, another key molecule in the origin of life, may have occurred in space over four billion years ago. Glycerol is an essential component in triglycerides, fats and oils that are necessary for energy in the body, and in phospholipids, the main component of the plasma membrane of cells. The scientists simulated how glycerol could have been made by ionizing radiation in ice similar to that found in space, which was then transported via meteorites to Earth.
The team in Hawaii cooled icy sand grains coated with methanol in an ultra-high vacuum chamber down to 5 Kelvin, which is five degrees above absolute zero. They then bombarded the icy sand with high-energy electrons to reproduce the cosmic rays found in space. The methanol coated material reacted to form complex organic compounds, particularly glycerol.
The key researchers Ralf Kaiser, Surajit Maity and Brant Jones hope that their work will spark further elucidation of the origin of macromolecules. They are using cutting edge lasers and ultraviolet light in a vacuum to investigate the newly produced molecules. Their work challenges an earlier hypothesis that glycerol was synthesized on Earth under low temperature conditions that could foster the creation of these prebiotic cell components. The researchers are also investigating the formation of nucleotides.
Scientists have also shown common origins of RNA, protein and lipid precursors by examining the assembly of different biomolecular building blocks from plausible prebiotic intermediates and one-carbon feeder molecules. Researchers Bhavesh H. Patel et. al. published in Nature Chemistry in March 2015 that precursors of ribonucleotides, amino acids and lipids can all be derived by the reductive homologation of hydrogen cyanide, demonstrating that all these cellular subsystems could have arisen simultaneously through common chemistry. Similar to the work of the NASA researchers and the team in Hawaii, the key reaction steps here too are driven by ultraviolet light.
Will we ever know how humans arose on Earth and how feasible life is on other planets? The groundbreaking work of these researchers and others around the globe are bringing us closer to the answers.