Life-changing experiments: The biological Higgs : Nature News & Comment
"Biologists ponder what fundamental discoveries might match the excitement of the Higgs boson."
The author, Heidi Ledford, lists these ones:
Is there life elsewhere?
Exobiology has been panned by some eminent scientists, like paleontologist George Gaylord Simpson, as a science without a subject.
But Christopher Chyba has responded that it's no worse than looking for predicted elementary particles like the Higgs particle.
Chris McKay proposes to three places to look in the Solar System:
- Mars, though “old Mars, not Mars today”.
- Europa, one of Jupiter's moons
- Enceladus, one of Saturn's moons
Mars has a lot of evidence of a former ocean of liquid water in Vastitas Borealis, and likely elsewhere, like in Hellas Planitia.
Any organisms on Europa or Enceladus would have to be in those moons' interiors. Their surfaces are icy, but there's plenty of evidence of liquid water underneath. Enceladus makes geysers, while Europa shows evidence of geologically recent resurfacing.
Any organisms still living on Mars must be living below its surface, in cracks and pores in Mars's rocks, as some Earth organisms do.
Is there foreign life on earth?
The big challenge is how to detect such organisms, since they would likely not have any recognizable heredity-molecule content, no DNA or RNA to be detected by typical lab techniques.Alien life — and a Higgs moment — might also be lurking close to home. Some have postulated the existence of a 'shadow biosphere' on Earth, teeming with life that has gone undiscovered because scientists simply don't know where to look. It could contain life that relies on a fundamentally different biochemistry, using different forms of amino acids or even entirely novel ways of storing, replicating and executing inherited information that do not rely on DNA or proteins.
One would have to isolate such organisms and grow them in quantity in the lab before one can confidently conclude that they are DNA-less or RNA-less.
The RNA world is a speculation that has been getting a lot of support, but no free-living RNA organisms or RNA-protein ones have ever been found, only DNA-RNA-protein ones. Viruses don't count, because they are parasitic on their host cells' transcription and translation systems. RNA or RNA-protein organisms may be distantly related to known ones, but even if they were, they would still be an important find.
But there has been at least one major flub in this field:
I won't believe it unless someone crystallizes DNA or RNA from that organism and then does X-ray crystallography on it. If it has arsenates instead of phosphates in its structure, the arsenic atoms should be easily distinguishable from phosphorus ones. Arsenic has atomic number 33 and phosphorus 15, meaning about twice as many electrons for an X-ray photon to bounce off of.Felisa Wolfe-Simon, now at the Lawrence Berkeley National Laboratory in Berkeley, California, and her colleagues took this approach when they searched for life in the arsenic-rich environment of California's Mono Lake. In late 2010, they reported the discovery of a life form that can use arsenic in place of phosphorus in its DNA and proteins — a seemingly remarkable departure from conventional life. But at least one attempt to reproduce the result has failed.
How did life start…?
Mentions the RNA world, which is nowadays often treated as if it was well-established. It successfully resolves the mutual dependency of DNA, RNA, and protein in present-day organisms by featuring RNA as both informational molecule and enzyme. Some coenzymes (molecules that work with enzymes) have bits of RNA in them; these are likely vestigial features of the RNA world. Proteins were originally invented as coenzymes; they eventually took over and became the main enzymes. However, they could not take over information storage. DNA was invented as a modification of RNA, and DNA building blocks are still made from RNA ones.
However, there is the serious question of the origin of the RNA.In 2009, a paper from Joyce's lab reported the development of a system of RNA molecules that undergo self-sustaining Darwinian evolution5. But enzymes and a human hand were needed to create the RNA sequences to start off the reaction, Joyce says, and so far his lab has not found conditions that would allow the system to form spontaneously. “We're still a bit challenged,” he says. “But the system is running more and more efficiently all the time.”
The ribose part of RNA has 4 asymmetric carbon atoms, while most amino acids have only 1, and the wrong asymmetries will cause major incompatibilities. It's also difficult to make ribose prebiotically. It's possible to do it by condensing formaldehyde (the formose reaction), but one needs it to be reasonably pure, and one gets a big mess of sugarlike molecules.Some believe that RNA may have had a precursor. Ramanarayanan Krishnamurthy at the Scripps Research Institute, is testing novel polymers of organic chemicals that could have formed in the primordial goo, in search of those that could replicate and evolve. “RNA was not the first living entity,” says Bada. “It's too complex. Something preceded RNA, and that's where the interest is right now.”
So RK and others have been working on what might have preceded the ribose part of RNA.
… and can we delay its end?
Giving mice something called rapamycin will make them live longer: 10% for males and 18% for females. Cutting calorie intake by 25-40% can also extend lifespan.In a 1993 review, Linda Partridge and Nicholas Barton, both then researchers on ageing at the University of Edinburgh, UK, delivered “a baleful message” to the field of gerontology. The complexity of the biological networks that influence ageing, they wrote, means “it is most unlikely that engineering of a few genes or intervention in a handful of physiological pathways will prevent the process from occurring.”
Things have changed. “I could tolerate that debate 20 years ago,” says Richard Miller, who studies ageing at the University of Michigan in Ann Arbor. “But now it's just wrong.”
Some eight months after the publication of Partridge and Barton's review, Cynthia Kenyon and her colleagues at the University of California, San Francisco, reported that mutations in a single gene allowed the nematode Caenorhabditis elegans to live more than twice as long as usual. Three years later, a group led by Andrzej Bartke, who studies ageing at Southern Illinois University in Springfield, reported that mice bearing a single mutation that causes hormonal deficiencies live up to 68% longer than mice without the mutation.
Despite these successes,
Ageing, however, “is almost the complete inverse of the situation of the Higgs particle”, reflects Thomas Kirkwood, a leader in the field at Newcastle University, UK. “Everything that we're learning tells us it's highly unlikely that we'll find a single unitary cause.”