Magnetic fields and the Q

Sorry, not for Trekkies. This Q is chemical.

People have been concerned for years about magnetic fields having adverse health effects–or even have peddled magnets as being health beneficial. But although scientists have demonstrated repeatedly a chemical response to magnetic fields, no one has ever shown the magnetic fields directly affecting an organism.

The earth’s core is weakly magnetic, the result of the attraction between electric currents moving in the same direction. Nature presents plenty of examples of animals that appear to use magnetic fields. Some bacteria can detect the fields and use them for movement. Birds appear to use magnetic fields to navigate, and researchers have shown that attaching magnets to birds interferes with their ability to navigate. Honey bees become confused in their dances when the earth’s magnetic fields fluctuate, and even amphibians appear to use magnetism for navigation. But no one has clearly demonstrated the mechanism by which animals sense and use magnetic fields.

Do pigeons use a compass?

Some research points to birds using tiny magnetic particles in their beaks to fly the right way. But these particles don’t tell the birds which way is north; they simply help the bird create a topographical map in its head of the earth over which it flies. The magnetic particles tell a pigeon there’s a mountain below, but not that the mountain is to the north. The conundrum has been to figure out how the pigeon knows which way is north in the absence of other pointers, such as constellations.

The answer to the conundrum lies with the bacteria. Scientists in the UK have used the purple bacterium Rhodobacter sphaeroides to examine what magnetic fields do at the molecular level. These bacteria are photosynthetic, and absorb light to convert to energy in the same way plants do. The absorbed light triggers a set of reactions that carry energy via electrons to the reaction center, where a pigment traps it. Under normal conditions, as the pigment traps the energy, it also almost instantaneously converts it to a stable, safe form, but sometimes the energy can form an excited molecule that can be biologically dangerous. As it turns out, these reactive molecules may be sensitive to magnetic fields.

A radical pair…or dangerous triplet

A chemical mechanism called the “Radical Pair Mechanism” is the method by which the potentially dangerous molecules can form. In this mechanism, an electron in an excited state may pair with another type of electron in an excited state. If the two excited molecules come together, they can form what is called a “radical pair in a singlet state,” because they are two singlets that have paired. Under normal conditions, this pairing does not happen; in the photosynthetic bacterium, for example, a compound called a quinone (Q) inhibits formation of this pair or of an equally damaging triplet of one electron type or the other.

But when a Q is not present, the singlet or triplet state results. If the triplet forms, it can interact with oxygen to produce a highly reactive, biologically damaging singlet molecule that we know as a “radical.” You have probably heard of radicals in the context of antioxidants—they are the molecules that antioxidants soak up to prevent their causing harm. You may also have heard of carotenoid, a pigment that is an antioxidant. In a normal photosynthetic bacterium, the carotenoids present serve as the Q, the compound that prevents formation of the damaging radical.

A helpful effect of magnetic fields?

Where do magnetic fields come in? Previous work indicated an influence of magnetic fields on triplet formation, and thus, on radical formation. One excellent model to test the effects of fields in a biological system is to remove the Q, the molecular sponge for the triplets, and then apply magnetic fields to see whether triplets—and radicals—form.

That’s exactly what the researchers did, using a mutated form of R. sphaeroides that did not make carotenoids—the Q. The result? The stronger the field, the less radical product was made. They have demonstrated a magnetic field effect in an organism for the first time, and the effect was helpful, not damaging. Their next step, which they are working on, is examining whether or not the bacteria grow better in the presence of the fields.

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Why is the sky blue? Blame rocks

Early Earth’s changing landscape…and skyscape

If you traveled back in time to about 2.5 billion years ago, you wouldn’t recognize much of what you saw. The dawning, living planet back in the day sported skies of orange, shaded by an unbreathable atmosphere awash in methane gas. But through the long Proterozoic Era, those skies changed from orange to blue. Usually, we give our thanks for this change to oxygen, but a recent review traces the original actor in the color change drama to rocks. Specifically, to the phosphorus in the rocks.

Phosphorus? Really?

Phosphorus is one of the critical of elements of life. It’s a primary component of a DNA or RNA building block (nucleotide = sugar, phosphate, base). It also happens to be the primary component of the “energy currency” of cells, ATP, or adenosine triphosphate, which is really a nucleotide with three phosphates on it. Many organisms use ATP, and all organisms use phosphorus in their genetic code and their RNA.

And, a major source of it is rocks. So, yes. Phosphorus, really. Read on.

Geochemical cycles and a whole lot of gas

Several independent lines of evidence have shown that oxygen levels rose in two lengthy bursts coincident with bursts of life on Earth. The first gassy increase happened between 2.5 to 2 billion years ago. Fittingly, scientists refer to this rise in atomspheric oxygen as the Great Oxidation Event. One of the effects of the increased oxygen is that rust started showing up in the geologic record. During this Great Event, the single-celled organisms that had thrived under a presumably orange sky grew larger, and mitochondria may have arisen as a result of endosymbiosis. These cellular powerhouses are, in fact, responsible for completing energy extraction from organic molecules and using the energy to build…ATP.

The second big burst of oxygen happened about 1 billion to 540 million years ago, this time coincident with the rise of multicellular organisms and culminating in the blast of diversificiation known as the Cambrian Explosion.

What does oxygen have to do with phosphorus?

The two often hang out together as phosphate, but the real connection here is about phosphate’s contribution to life’s explosions. It may be that geologic processes, such as erosion, caused a gradual but abundant release of phosphorus from rock into the Earth’s seas. With this influx of a key component for building life, the phosphorus facilitated the early Earth equivalent of enormous algal blooms.

And guess what those algae did…and still do? Photosynthesisis. And one of the main byproducts they release from all that busy light capturing and sugar building is…oxygen. That’s the phosphorus-oxygen connection.

So, if a child ever asks you why the sky is blue and you just can’t think of the answer, you can distract them by asking them, “Did you know that the sky used to be orange?”

For your consideration

Double-membrane organelles like mitochondria are thought to have arisen through a process called endosymbiosis. What is endosymbiosis, and how could it have led to the presence of organelles like mitochondria in cells?

The algal blooms described in this paper were enormous and their influence may literally have changed the color of the sky back in the day, but the oxygen buildup and phosphorus release happened over long stretches of geological time. Today, we experience algal blooms, too. Can you identify the causes of these blooms? How do these blooms affect today’s life on Earth? Do the effects seem to be beneficial or adverse?

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