Michael Gibson

The Shape of DNA

In 1962, Francis Crick, James Watson, and Maurice Wilkins were awarded the Nobel Prize in Physiology or Medicine. They had determined that DNA is made of two chains that spiral around each other in a structure called a double helix.

Spiraled chains, like those of DNA, have “handedness.” To understand handedness, think about your own hands. Left and right hands are mirror images of each other. If you place your hands palm to palm and imagine a mirror between your palms, your actual right hand would be oriented no differently from the reflected image of your left hand.

Most DNA in our bodies is right-handed. In a helix, right-handed means that if you traced a finger up one strand of the spiral, that finger would travel in the same direction as if you curled the pointer finger of your right hand toward that palm and continued to make circles in this direction. If you look directly down at a right-handed helix from the top, the incline spirals counter-clockwise. If you used your left pointer finger in the same way, you would trace a clockwise spinning left-handed helix, a mirror image of the right.

Scientists call molecules with handedness “chiral”, to reflect how these molecules are not the same as their opposites. Chiral molecules have different three-dimensional structures, and therefore can behave differently. Short sequences of our DNA sometimes turn into left-handed spirals by un-spiraling and twisting the opposite way. This left-handed DNA is called Z-DNA. It behaves differently from its right-handed counterpart, for example having a suspected role in some cancers.

The handedness of DNA reveals how much our knowledge of DNA has changed in the last 70 years. Z-DNA wasn’t discovered until about three decades after Crick and Watson began working together and now, more than 30 years after the Z-DNA publications of the late 1970s and early 80s, our understanding of DNA has advanced even further. We have sequenced the DNA of humans and many other organisms and are working on using techniques like CRISPR to edit DNA. How much more do we have to learn about DNA over the next three decades and what more can we learn and be able to do?

Learn more about DNA and consider the answers to these questions in the Perot Museum’s Being Human Hall where you can even grab a lab coat and conduct experiments of your own in the BioLab, presented by Children’s Health.

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