Monday, October 17, 2005

Every structure has a story

It's been a long nitpicky journey but it's nearing the end. The almost-final version of the instructor manual, for "Exploring DNA Structure," has been sent off to the printer and there's nothing I can do now except patiently wait. In a week or so, I'll get to review it one more time in printed form and then release it to the world in November.

My family is quite relieved. For the past few week, I've been in distant space contemplating things yet to be done and obsessing about items that need to get checked off the list. It's gotten so bad that I spend soccer games thinking about margin size or I take the dog for a walk and stop suddenly to tell my husband that I must check the index one last time and make sure that all that chapters are starting on the right side of the page.

It's all worth it, though. I confess I've become totally entranced with molecular structures. They are the most fascinating art form I've ever seen and every structure has its own story. I know because I read and wrote 69 structure stories for the "Exploring DNA Structure" instructor guide. This was never in my original plan but my friend Charlotte Mulvihill wrote to ask me about the functions of different structures. I blithely replied that sometimes the only function was to satisfy the curiosity of the researchers. Then, I started to wonder, too, and couldn't help reading about all of them and compiling an answer guide for the manual.

The more I learned, the more fascinated I became. Some of my favorites are shown below.

Many structures on the CD contain anti-cancer or antiviral drugs bound to DNA. These drugs kill cancer cells by making it hard for cells to copy, unwind, or repair their DNA. Although these drugs harm all growing cells, cancer cells suffer the most damge since they grow more rapidly than normal cells. This image shows tamoxifen, a drug used to treat breast cancer, bound to DNA.

Telomeres protect the ends of linear, eucaryotic chromosomes. Unlike the rest of the chromosome, with double-stranded or duplex DNA, telomeres form four-stranded quadruplex structures with lots of positively charged ions. I think the ions probably shield the negatively charged phosphates and allow the strands to get close together.

DNA can form interesting loop structures where a single-strand kind of twists around back on itself. This structure is thought to regulate expression of the protective antigen gene, in Bacillus anthracis, the bacteria that cause antrax. The protective antigen plays a key role in development of anthrax symptoms. If we can understand how this gene is turned on or off, perhaps we can find a way to turn this gene off and prevent the symptoms altogether.

Recombination intermediates, also known as Holliday structures, are wild. When I was an undergraduate, I found recombination to be very mysterious. This structure shows DNA in the act of breaking and joining to other strands. Seeing the structures makes genetics less mysterious and considerably more fun.


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