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3-D imaging improves understanding of supercoiled DNA

DNA is nature's ultimate data storage device, but we are only beginning to understand how it operates. Using Cryo-electron tomography, scientists are learning how DNA acts when uncoiled.

We often think of DNA as that simple, beautiful twisting double helix so popularized by modern culture. While this view isn’t exactly incorrect, it’s very limited. In real life, DNA is an immensely complex molecular structure, and only now are scientists beginning to understand the myriad of shapes it can take on.

Using cryo-electron tomography,  researchers are learning more about how DNA functions while in biological use, and specifically the many shapes and forms it can take. Cryo-electron tomography refers to the process of freezing biological samples.

This microscopy technique makes it easier for researchers to observe tiny and frequently changing biological samples.

DNA is a tightly coiled molecular structure, containing an estimated 3 billion base pairs. If fully unwound, DNA would stretch three feet (yes, three feet) in length. This massive structure, however, needs to fit inside the tiny nucleus of cells, where the DNA is stored when not being used.

The only way to fit that much into a space so tiny is to wind it, very, very tightly.

Of course, our cells need to access the data in DNA, from time to time, and cannot do so while it’s all wound up. In order to work with it in a variety of biological processes, our cells need to modify the shape of the DNA itself.

When cells need to use DNA, it is pulled out of the nucleus, unwound, and then worked with. Our understanding of DNA once it is unwound has generally been very limited.

Up until now, trying to anticipate and work with this myriad of shapes has been difficult, but scientists are now using 3-D imaging software and cryo-electron tomography to learn more about the twisting and turning shapes of DNA.

Even with the massive power of modern computers, researchers aren’t yet working with the full length of DNA. Instead, researchers are working with small DNA “circles”, bending and twisting them to see how the DNA reacts and shapes.

These tiny circles were about 10 million times shorter than an actual DNA strand, but by the standards of modern genetics, these structures themselves are quite massive and difficult to work with.

 

A brief overview of DNA

DNA was discovered by Francis Crick and James Watson in 1953. Needless to say, the discovery of DNA marked one of the biggest achievements of the 20th century. DNA stands for Deoxyribonucleic acid, which is one of the three macromolecules believed to be required for life. (The other two are proteins and carbohydrates).

The science is immensely complex, but essential DNA provides instructions to the cells, telling them what to do. Everything from the structure of our bones, to the color of our eyes is determined by the instructions handed out from DNA.

The only part of our body that doesn’t seem to function on the DNA found in the nucleus of our cells is the mitochondria, which actually has its own set of DNA instructions. For this reason, some believe that mitochondria originally evolved separately from most organic animal cells.