Posts Tagged ‘biology’
New evidence that Alzheimer’s disease is infectious [Brains]
22
Oct
We may be even more alone in the universe than we thought [Evolution]
22
Oct
Marathon Math: How Not to Hit the Wall
21
Oct
A marathoner’s worst nightmare — hitting “the wall†— may be completely avoidable if athletes adhere to personalized pace limits proposed by a biomedical engineer and runner. Benjamin Rapoport’s mathematical formula, published online Oct. 21 in PLoS Computational Biology, shows the speediest pace any marathoner can sustain for the entire race.
“A 10-second difference in pace per mile could make the difference between success and a dramatic failure,†says Rapoport, of Harvard Medical School and MIT, who experienced his own traumatic wall splat in the 2005 New York City Marathon. He started out pushing too hard, he says, and was out of steam by the last few miles. Rapoport finished, but with a slower time than he wanted.
To avoid this scenario, a runner has to maintain a pace that conserves carbohydrates, the body’s main source of quick-burn energy, all the way to mile 26.2. Rapoport calculates the ideal pace from a measure of aerobic capacity called VO2max, along with a few other variables. VO2max indicates how efficiently a body consumes oxygen.
“This is a unique area that hadn’t been addressed in the medical literature in any substantial way,†says Mark Cucuzzella, a physician and running coach based in Harpers Ferry, W.Va. “He’s lending some hard numbers to what experienced runners and coaches have been doing.â€
A man with a VO2max of 60 — which, after training, is attainable by only the top 10 percent of male runners — can achieve a 3:10 marathon finish time, according to the model. This time happens to be the cutoff for 18- to 34-year-old men to qualify for the Boston Marathon.
Elite male marathoners clock in with a VO2max in the high 70s. The average untrained young man’s number is in the 40s. (Incidentally, Rapoport, who has run 18 marathons, has a VO2max above 70 and breezes through marathons in less than three hours.)
VO2max is usually measured with specialized equipment while someone exercises at maximum exertion, but the value can also be estimated by measuring heart rate while running at a constant pace.
Rapoport’s model also shows that a slightly faster pace can be maintained by consuming a midrace snack.
This carb-eating strategy can help, but it can’t win races, since the body can store only so much fuel, says Cucuzzella, chief medical consultant for the Air Force Marathon and a marathoner himself. “It’s not about how much sugar or spaghetti you eat the night before a race,†he says. “There’s a critical pace.â€
Rapoport plans to put an easy-to-use version of his formula on the Internet to help runners calculate their ideal pace. “My primary goal is to give any marathon runner a qualitative plan for their training,†he says.
Image: Flickr/Stijn Bokhove
See Also:
- The Potential for a 40-MPH Man
- To Run Better, Start by Ditching Your Nikes
- These Toes Were Made for Running
- Bolt Is Freaky Fast, But Nowhere Near Human Limits
Where on Earth do these extraterrestrial toadstool trees grow? [Madgeography]
13
Oct
Comet impact shockwave may have planted seeds of life on Earth
13
Sep
Stanley Miller performed some of the most famous origin of life experiments, showing that the chemicals thought to be present in the early Earth's atmosphere might react to form amino acids, the building blocks of proteins. But these experiments haven't aged well, through no fault of their own; other scientists have since revised their estimates of what was present in the early atmosphere, raising some doubts as to whether the Miller experiments are especially relevant. A paper released by Nature Chemistry neatly dodges this issue by showing that it might not matter what the Earth looked like—the shockwave of a comet impact can make biological materials regardless of the composition of the atmosphere it crashes into.
In the years since Miller's experiments, we've been better able to image the composition of comets, and have even returned samples of some of the material shed by the comet Wild 2 as it approached the Sun. These have revealed a mixture of simple organic compounds like ammonia and ethanol, but nothing as complex as an amino acid, chemicals that form the building blocks of proteins.
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Mass Extinctions Change the Rules of Evolution
02
Sep
A reinterpretation of the fossil record suggests a new answer to one of evolution’s existential questions: whether global mass extinctions are just short-term diversions in life’s preordained course, or send life careening down wholly new paths.
Some scientists have suggested the former. Rates of species diversification — the speed at which groups adapt and fill open ecological niches — seemed to predict what’s flourished in the aftermath of past planetary cataclysms. But according to the calculations of Macquarie University paleobiologist John Alroy, that’s just not the case.
“Mass extinction fundamentally changes the dynamics. It changes the composition of the biosphere forever. You can’t simply predict the winners and losers from what groups have done before,†he said.
Alroy was once a student of paleontologist Jack Sepkoski, who in the 1980s formalized the notion that Earth has experienced five mass extinctions in the 550 million years since life became durable enough to leave a fossil record. Graphs of taxonomic abundance depict lines rising steadily as life diversifies, plunging precipitously during each extinction, and rising again as life proliferates anew.
As the fossil record is patchy and long-term evolutionary principles still debated, paleobiologists have historically disagreed about what these extinctions mean. Some held that, in the absence of extinctions, species would diversify endlessly. The Tree of Life could sprout new branches forever. Others argued that each taxonomic group had limits; once it reached a certain size, each branch would stop growing.
Sepkoski’s calculations put him on the limits side of this argument. He also proposed that, by looking at the rate at which each group produced new species, one could predict the winners and losers of each mass extinction’s aftermath. Groups that diversified rapidly would flourish. Their destiny was already established.
“It’s a clockmaker vision of evolution. Each group has fixed dynamics, and if there’s an extinction, it just messes it up a bit,†said Alroy. “That’s what I’m challenging in this paper. There are limits, and that’s why we don’t have a trillion species. But those limits can change.â€
Alroy crunched marine fossil data in the Paleobiology Database, which gathers specimen records from nearly 100,000 fossil collections around the world. He used a statistical adjustment method designed to reduce the skewing influences of paleontological circumstance — the greater chances of finding young fossils rather than old, the ease of studying some types of rock rather than others.
Historical species diversity among marine animals of Cambrian, Paleozoic and Modern origin.
The analysis, published September 2 in Science, produced what Alroy considers to be the most accurate reflection of extinction dynamics to date. And while his data supported the notion that each group’s diversity eventually hits a limit, he didn’t find Sepkoski’s correlation between pre-mass-extinction diversity rates and post-extinction success. Each mass extinction event seemed to change the rules. Past didn’t indicate future.
In an accompanying commentary, paleontologist Charles Marshall of the University of California, Berkeley noted that Alroy’s statistical methods still need review by the paleobiology community. The Paleobiological Database, for all its thoroughness, might also be incomplete in as-yet-unappreciated ways. “There will be no immediate consensus on the details of the pattern of diversity,†he wrote. But “the pieces are falling into place.â€
Enough pieces have come together for Alroy to speculate on his findings’ implication for the future, given that Earth is now experiencing another mass extinction. Starting with extinctions of large land animals more than 50,000 years ago that continued as modern humans proliferated around the globe, and picking up pace in the Agricultural and Industrial ages, current extinction rates are far beyond levels capable of unraveling entire food webs in coming centuries. Ecologists estimate that between 50 and 90 percent of all species are doomed without profound changes in human resource use.
In the past, many evolutionary biologists thought life would eventually recover its present composition, said Alroy. In 100 million years or so, the same general creatures would again roam the Earth. “But that isn’t in the data,†he said.
Instead Alroy’s analysis suggests that the future is inherently unpredictable, that what comes next can’t be extrapolated from what is measured now, no more than a mid-Cretaceous observer could have guessed that a few tiny rodents would someday occupy every ecological niche then ruled by reptiles.
“The current mass extinction is not going to simply put things out of whack for a while, and then things will go back to where we started, or would have gone anyway,†said Alroy. Mass extinction “changes the rules of evolution.â€
Images: 1) A fossil skull of Dunkleosteus, an apex predator fish that lived between 380 million and 360 million years ago, and had what is believed to be history’s most powerful bite./Michael LaBarbera, courtesy of The Field Museum. 2) Graph of species diversity among marine animals of Cambrian, Paleozoic and Modern origin./Science.
See Also:
- Ecosystem Engineering Could Turn Sprawl Into Sanctuary
- 9 Environmental Boundaries We Don’t Want to Cross
- Death Star Off the Hook for Mass Extinctions
- A New Explanation for Ancient Mass Extinction
- Latest Extinction is the Greatest
- Megafauna Extinctions Not Entirely Humans’ Fault
Citations: “The Shifting Balance of Diversity Among Major Marine Animal Groups.†By J. Alroy. Science, Vol. 329 No. 5996, September 3, 2010.
“Marine Biodiversity Dynamics over Deep Time.†By Charles R. Marshall. Science, Vol. 329 No. 5996, September 3, 2010.
Brandon Keim’s Twitter stream and reportorial outtakes; Wired Science on Twitter. Brandon is currently working on a book about ecological tipping points.
The smell of freshly-cut grass is actually a plant distress call [Mad Science]
26
Aug
Newly Discovered Chlorophyll Catches Infrared Light
20
Aug
A new kind of chlorophyll that catches sunlight from just beyond the red end of the visible light spectrum has been discovered. The new pigment extends the known range of light that is usable by most photosynthetic organisms. Harnessing this pigment’s power could lead to biofuel-generating algae that are super-efficient, using a greater spread of sunlight than thought possible.
“This is a very important new development, and is the first new type of chlorophyll discovered in an oxygenic organism in 60 years,†says biological chemist Robert Blankenship of Washington University in St. Louis.
The newfound pigment, dubbed chlorophyll f, absorbs light most efficiently at a wavelength around 706 nanometers, just beyond the red end of the visible spectrum, researchers report online August 19 in Science. This unique absorbance appears to occur thanks to a chemical decoration known as a formyl group on the chlorophyll’s carbon number two. That chemical tweak probably allows the algaelike organism that makes chlorophyll f to conduct photosynthesis while living beneath other photosynthesizers that capture all the other usable light.
“In nature this very small modification of the pigment happens, and then the organism can use this unique light,†says molecular biologist Min Chen of the University of Sydney in Australia. Chen and her colleagues identified the new pigment in extracts from ground-up stromatolites, the knobby chunks of rock and algae that can form in shallow waters. The samples were collected in the Hamelin pool in western Australia’s Shark Bay, the world’s most diverse stromatolite trove.
Previously there were four known chlorophylls made by plants and other photosynthesizing organisms that generate oxygen: a, b, c and d. Chlorophyll a, the standard green type, is found in photosynthesizers from algae to higher plants. It absorbs mostly blue light around 465 nanometers and red light around 665 nanometers (it reflects green light, hence plants look green). Chlorophylls b and c are found in fewer organisms and absorb light in a similar range as chlorophyll a does, but shifted a bit. Chlorophyll d, found in a specific group of cyanobacteria, absorbs the most light at roughly 697 nanometers, a slightly shorter wavelength than the absorption of the new chlorophyll.
While some bacteria make chlorophyll-like pigments that absorb even longer wavelengths of light, these creatures aren’t harnessing light to split water, the step in photosynthesis that generates oxygen. Scientists didn’t think that wavelengths absorbed by chlorophyll f would have enough oomph to split water either, but it turns out they do, says Chen.
“This challenges our conception of the limit of oxygenic photosynthesis,†she says.
The find may also enable scientists to engineer algae that are more efficient producers of oil for biofuels, says algae biologist Krishna Niyogi of the University of California, Berkeley. Microbes bearing the new chlorophyll could soak up rays that most microbes can’t make use of.
There is still much to be learned about the new type of chlorophyll and the organisms that make it, Niyogi says. Chlorophyll f was extracted from the ground-up stromatolites along with a lot of chlorophyll a. It isn’t clear what creature was making chlorophyll f, but evidence points to a filamentous cyanobacterium. This cyanobacterium might use both chlorophylls, or perhaps just f.
Images: 1) Red-shifting cyanobacteria./Science. 2) Shark Bay stromatolites./Wikimedia Commons.
See Also:
- Perforated Blobs May Be Earliest Known Animals
- Green Sea Slug Is Part Animal, Part Plant
- Everywhere in a Flash: The Quantum Physics of Photosynthesis
- Leafy Green Coherence: Quantum Physics Fuels Photosynthesis …
Muscles Remember Past Glory
16
Aug
Pumping up is easier for people who have been buff before, and now scientists think they know why — muscles retain a memory of their former fitness even as they wither from lack of use.
That memory is stored as DNA-containing nuclei, which proliferate when a muscle is exercised. Contrary to previous thinking, those nuclei aren’t lost when muscles atrophy, researchers report online August 16 in the Proceedings of the National Academy of Sciences. The extra nuclei form a type of muscle memory that allows the muscle to bounce back quickly when retrained.
The findings suggest that exercise early in life could help fend off frailness in the elderly, and also raise questions about how long doping athletes should be banned from competition, says study leader Kristian Gundersen, a physiologist at the University of Oslo in Norway.
Muscle cells are huge, Gundersen says. And because the cells are so big, more than one nucleus is needed to supply the DNA templates for making large amounts of the proteins that give muscle its strength. Previous research has demonstrated that with exercise, muscle cells get even bigger by merging with stem cells called satellite cells, which are nestled between muscle fiber cells. Researchers had previously thought that when muscles atrophy, the extra nuclei are killed by a cell death program called apoptosis.
Memory holding nuclei on muscle fiber light up in green.
In the new study, Gundersen’s team simulated the effect of working out by making a muscle that helps lift the toes work harder in mice. As the muscle worked, the number of nuclei increased, starting on day six. Over the course of 21 days, the hard-working muscle increased the number of nuclei in each fiber cell by about 54 percent. Starting on day nine, the muscle cells also started to plump up, adding an extra 35 percent to their volume. Those results indicate that the nuclei come first and muscle mass is added later.
In another set of experiments, the researchers worked the mice’s muscles for two weeks and then severed nerves leading to the muscle so the tissue would atrophy. As the muscle atrophied, the cells deflated to about 40 percent of their bulked-up volume, but the number of nuclei in the cells did not change.
These results contradict previous studies that show lots of cell death in muscles during atrophy. Gunderson’s team examined individual cells in the wasting muscles and found that there is apoptosis going on, but that other cells are dying, not the muscle fibers or their extra nuclei. The extra nuclei stick around for at least three months — a long time for a mouse, which lives a couple of years on average, Gundersen says.
“I don’t know if it lasts forever,†he says, “but it seems to be a very long-lasting effect.†Since the extra nuclei don’t die, they could be poised to make muscle proteins again, providing a type of muscle memory, he says.
“That’s fascinating thinking, and there’s nice proof in this article to support it,†says Bengt Saltin, a muscle physiologist at the University of Copenhagen in Denmark. “It’s really novel and helps to explain descriptive findings that muscles are quick to respond upon further training.â€
The study is likely to provoke strong reaction from some researchers, says Lawrence Schwartz, a cell biologist at the University of Massachusetts Amherst.
“It does fly in the face of a lot of peer-reviewed, published data,†he says. But the selective death of just some of the nuclei in a muscle cell would require a special kind of apoptosis. “The conventional wisdom doesn’t make much sense from a cell and molecular perspective,†Schwartz says. Gunderson’s group has come up with an explanation that seems more plausible. “Their data just feels right.â€
If the results hold up in people, sports agencies may want to reconsider how long they ban athletes suspended for taking steroids. Previous research has shown that testosterone boosts the number of nuclei in muscle cells beyond the amount produced by working out. “If you have nuclei that last forever, then you would also have an advantage that could last forever,†Gundersen says.
Well, maybe not exactly forever. As people age, their ability to build muscle mass declines. The new study suggests that pumping muscles full of nuclei early in life could help stave off muscle loss with age. “This could be an argument for mandatory physical training in schools,†Saltin says.
See Also:
- Salamander Regeneration Trick Builds New Mouse Muscle
- Athletes Beware, Scientists Hot on Gene Doping Trail
- Human Centrifuge Preserves Muscle at Zero-G
- Direct Brain-to-Muscle Electrical Circuit Helps Paralyzed Monkeys
- The Marvelous Muscles of the Mud-Loving Toadfish
- Genetic Switch Could Restore Memory
Images: 1) left to right: Nubret, Schwarzenegger, Lou Ferrigno, ca. 1975. Flickr/d_vdm. 2) J.C. Bruusgaard/University of Oslo
We may have been looking at the wrong DNA for the secrets of longevity [Mad Genomics]
05
Aug
