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Sunlight’s Dark Side

Posted by | June 20, 2009

These are the longest days of the year, with the sun higher in the sky than at any other time. Like many people living in the northern strip of the country, I used to spend a good bit of time worshipping the sun each June. I didn’t use any sunscreen because I found that after a few days outdoors, my exposed parts were red-brown – and my chronic joint pains were cut in half.

I knew strong sunlight on Scandinavian skin was a recipe for trouble. But reducing joint pain in-the-present tended to trump my fears of death down-the-road. I’m rethinking my tactics a bit this year, however, and taking more Vitamin D as tablets.

Sunlight feels like such a blessing – especially to us Northern people – it’s easy to wonder how it can kill. The answer lies in the fact that our genetic blueprint is recorded on a tissue of molecules that’s both remarkably flexible and exceedingly fragile.

The blueprint – known as the DNA molecule – is a long chain of chemicals wrapped around each other in simple and complex ways. Like a telephone cord that makes tight curls around itself, and looser curls as it flops on your desk, DNA can be wound both tightly on a fine scale and more loosely overall at the same time. It’s amazing to me, but the coils are also folded over in complex ways, a bit like little paper cranes from art class. The coils and folds make it possible for an enormous amount of DNA to fit inside the nucleus of your cells.

“It’s like packing a great deal of spaghetti into an itty-bitty can,” said biochemistry professor Michael Smerdon of Washington State University to me.

It’s mind-bogglingly complex in detail, at least to a simple-hearted geologist like me.

“That’s not just you,” Smerdon said kindly. “Biology is chaos, a cesspool of complexity.”

But one simple truth is that the complex DNA our lives depend on is damaged many, many times each day in each and every one of our cells. That’s staggering to think about. I make a lot of mistakes each day at work as a writer, but my DNA creates errors in the basic chemical code of my life at a rate that leaves my many typographical mistakes in the dust.

Our lives are saved (usually) because we have some wonderfully well-developed systems for making repairs to DNA on the fly. Our cells each have great pit crews, if you will, that can put our DNA back to rights more or less every time we complete a lap on the racetrack. The repair crews have to cope with the closely looped and folded parts of the DNA, and the slightly looser bits, no easy task in itself. It doesn’t  always work out right, but mostly it does, and sometimes the continued mistakes don’t matter. A combination of those two factors keeps us going.

But the whole dynamic of frequent errors and endless fixes can change when strong sunlight slices through our skin cells. The energy of the light – the same basic energy that makes sunlight warm – can damage some of the DNA, both in the closely and more loosely coiled sections of the complex spaghetti. Our natural “pit crews” do what they can to help, and mostly they do a good job. But if they miss doing a crucial repair, or the patch is simply wrong, one result can be that the cell gets the message to reproduce endlessly – and that’s part of what makes up cancerous lesions. That’s why letting your skin burn in the summers is a real risk.

The medical aspect of treatment is not something Smerdon and his research group address, just the fundamental biochemistry that’s at Square One of understanding the cells’ first-line of defense against DNA damage. But they know their work can be useful down-the-road to medicine.

“Einstein said there should be a 30-year lag from research discovery to application of results,” Smerdon said. “With biotechnology, it may be less now, but it’s still it’s a long time.”

Meanwhile, I’ll use my Vitamin D pills and try not to burn too badly this summer.