DNA mystery
Which came first: DNA or amino acids?
It’s an age-old question: Which came first, the chicken or the egg? A biologist studying how life began on Earth might phrase that question differently: Which came first, DNA or amino acids? DNA, the blueprint for making biological organisms that is in every living cell, provides the recipe to make amino acids. Groups of amino acids string together to make proteins. Proteins are basically responsible for building everything in a living organism, including more DNA.
DNA resembles a twisted ladder, the double helix, in every living cell. The ladder’s sides, the DNA backbone, is largely composed of 2-deoxyD-ribose, while the rungs are composed of complex sugars. Without 2-deoxyD-ribose, there is no DNA and without DNA, our cells have no idea which amino acids to make.
Amino acids are rather ubiquitous in our universe. They are easy to make, even in a high school science fair project. They’ve been discovered in meteorites, comets, even in the gaseous cloud of material surrounding newly-forming stars.
Recently, scientists from the University of York discovered a novel path to making DNA’s backbone. Dr. Paul Clarke from York’s Department of Chemistry said, “The origin of important biological molecules is one of the key fundamental questions in science. Scientists had already shown that there were particular molecules present in space that came to Earth in comet ice; this made our team at York think about investigating whether they could be used to make one of the building blocks of DNA. If this was possible, then it could mean that a building block of DNA was present before amino acids.”
They discovered that amino nitriles, the molecular precursors to amino acids, could trigger the formation of 2-deoxyD-ribose, of DNA. The process requires the presence of the interstellar molecules formaldehyde, acetaldehyde and glycolaldehyde — molecules found in cometary ices. Clarke said, “We have demonstrated that these interstellar building blocks can be converted in ‘one pot’ to biologically relevant carbohydrates — the ingredients for life.”
The answer to the biologist’s chicken-egg dilemma appears to be simple: natural chemistry, without the need for either chickens or eggs.
Planetary debris may give insights to early solar system
Most meteorites on Earth are fragments from much larger asteroids. These denizens of the asteroid belt between Mars and Jupiter occasionally collide, and the debris flies around the solar system, slamming into Earth and the other planets and moons. If a really large meteorite smashes into another body in the solar system, say our moon or Mars, fragments of that body may be blasted out into space. These fragments may eventually fall on Earth as meteorites. A small percentage of meteorites recovered here are actually pieces of the Moon and Mars. And, likewise, pieces blasted from Earth likely lay on the Moon, Mars, and even Venus and Mercury.
Bits of a planet’s atmosphere may also eventually end up on or around another planet or moon. Mars once had a much thicker atmosphere than it does now, but when its core solidified, Mars lost its magnetic field and the sun’s solar wind began slowly stripping it away. Today, the Martian atmosphere is only1 percent as dense as Earth’s.
The solar wind from our sun flows throughout the solar system. Earth is protected from the dangers of this charged radiation by our magnetic field. Like Mars, our Moon has no magnetic field. But for about five days each month, around the full moon, our natural satellite sits inside Earth’s protective magnetic field. During that time, some molecules of Earth’s atmosphere transfer to the Moon’s surface.
Recently, a Japanese spacecraft known as Kaguya found oxygen molecules from Earth in the lunar soil. Some of this oxygen is billions of years old. Studying this may allow scientists to understand exactly when and how oxygen became common in our atmosphere.
That’s not all that may be there. Astrobiologist Caleb Scharf of Columbia University says, “It’s not inconceivable that there are fossil organisms in Earth meteorites on the lunar surface.” If so, biologists may soon have a new method of studying Earth’s earliest biota.
October highlights: If you have a clear view of your eastern horizon, go outWednesday morning about 6:30 a.m. Look low in the eastern horizon for Venus, the brilliant “Morning Star.” If the sky is clear, you should be able to pick out ruddy Mars just below and to the right of Venus. Not a close conjunction, but an interesting one.
Planet visibility: As October begins, Venus, Mars and Mercury grace the morning predawn sky, although Mercury will be tough to locate, lying deep in the morning twilight. Saturn and Jupiter float in the evening sky after sunset, but Jupiter will be lost if you have trees to your west. By the end of the month, Jupiter and Mercury flip-flop, with Jupiter all but lost in the morning twilight and Mercury visible if you have a clear view of the western horizon after sunset. Saturn is still easy in the southwest after sunset. Mars moves farther from the sun in the morning sky, while Venus moves closer to the sun, but still easily visible in the morning twilight if you have a clear view of the eastern horizon. Full moon occurs on the Oct. 5 with new moon following on the Oct. 19.
Wayne Harris-Wyrick is an Oklahoma astronomer and former director of the Kirkpatrick Planetarium at Science Museum Oklahoma. Questions or comments may be emailed to wizardwayne@zoho.com.