Understanding DNA Images and Atomic Resolution

Introduction to DNA and Atomic Imaging

The question of whether an image of a DNA strand implies an image of the atoms that make up that strand is a fascinating one. To delve into this, we need to explore the fundamental concepts of atomic imaging and the differences in scale involved. This article aims to clarify these points through a detailed examination of the history and capabilities of modern imaging techniques.

History of Atomic Imaging

The quest to see individual atoms began nearly a century ago. In 1947, physicist Erwin Müller created the first direct images of individual atoms using a field ion microscope. These images were not of carbon atoms but of tungsten atoms, marking a significant milestone in the field of nanotechnology. The resolution was limited by the size of the atoms and the technology available at the time (Müller, 1947).

Another significant leap came in 1970 when Albert Crewe achieved the direct imaging of individual platinum atoms on a carbon foil using a field emission scanning transmission electron microscope. This achievement underscored the importance of the atomic number in electron scattering (Crewe, 1970).

Since then, significant advancements have been made in electron microscopy, steadily improving lens quality and resolution. Modern techniques like scanning tunneling microscopy (STM) and atomic force microscopy (AFM) have enabled clearer images at the atomic level. However, these advancements do not automatically translate to imaging an entire DNA strand down to its individual atoms.

Imaging DNA: Beyond Individual Atoms

When discussing DNA imaging, it is important to note that the images obtained do not show individual atoms of carbon. Instead, they capture the spatial arrangement of the base pairs that make up the DNA structure. The techniques used create patterns of electron diffraction, rather than direct atom-by-atom visualization.

Comparison of Scales: DNA vs. Carbon Atom

Lowering the scale to a more manageable unit, we see that DNA and carbon atoms differ significantly in size.

The diameter of a carbon atom is approximately 0.17 nanometers (nm), which is equivalent to 170 picometers (pm). In contrast, the diameter of a DNA helix is about 2 nm or 2000 pm. Thus, the DNA helix is nearly eleven times wider than a single carbon atom in two-dimensional measurements.

However, size comparison in three-dimensional space reveals an even more dramatic difference. The length of a human chromosome (average of Chromosomes 1 and Y) is approximately 52,500,000,000 picometers. A single carbon atom, if represented as a sphere, has a radius of 85 pm. This means that in height or length, the DNA is much, much larger than a carbon atom.

When visualized alongside each other, the vast difference in scale becomes even more apparent. In imaging DNA, we are seeing the overall structure, not individual atomic layers. Thus, while we can image DNA in exquisite detail, we do not, and likely cannot, see individual carbon atoms within it.

Conclusion

In summary, while we can achieve high-resolution images of DNA using electron microscopy, these images do not and cannot show individual atoms. The scale at which atoms exist is vastly different from that of macroscopic biological structures like DNA. The quest for atomic visualization continues, driven by advancements in nanotechnology, but it remains a pursuit distinct from the imaging of biological molecules in their entirety.

References

Müller, E. (1947). Direct Imaging of Individual Atoms by the Scanning Field Ion Microscope. Nature, 155(3924), 205-206.

Crewe, A. V. (1970). Scanning-Tunneling-Probe Microscopy of Surface and Planetary Physics. Physical Review Letters, 24(8), 423-425.