Visual science journalism’s DNA twist
Your left hand and right hand are mirror-images of each other. You can’t superimpose them completely even after all manner of rotations and translations. Only mirroring them works. The same thing can happen to some molecules. When two molecules are identical in every way except their geometric structure in space is such that one is a mirror-image of another, they’re said to be enantiomers. These molecules have a chirality, or handedness: like your hands, one is left-handed and the other right-handed.
On December 3, an international group of scientists published a technical report and commentary in Science warning against work to develop “mirror life”: cells whose chiral molecules are replaced with their complementary enantiomers. To quote from the commentary:
Our analysis suggests that mirror bacteria could broadly evade many immune defenses of humans, animals, and plants. Chiral interactions, which are central to immune recognition and activation in multicellular organisms, would be impaired with mirror bacteria. This could result in weakened immune recognition, a weakened response by innate immune systems, and (in vertebrates) limited downstream activation of adaptive immune functions. For example, experiments show that mirror proteins resist cleavage into peptides for antigen presentation and do not reliably trigger important adaptive immune responses such as the production of antibodies. We are thus concerned that the function of many vertebrate immune systems against mirror bacteria would be severely impaired. Invertebrate and plant immune systems are less well studied but appear to suffer analogous limitations.
Given the potential for severe immune evasion, mirror bacteria might not require host-specific factors to invade hosts and cause infection. In animals (including humans), bacteria regularly cross barriers in the skin, mouth, gut, lungs, and other mucosal surfaces because of routine damage and intrinsic leakiness; mirror bacteria would be expected to do the same. In healthy animals, translocated natural-chirality bacteria are typically cleared by immune defenses. However, if the immune response against mirror bacteria is sufficiently impaired, translocated mirror bacteria might replicate within the host and establish an infection. Unchecked replication of mirror bacteria within internal tissues is likely to be deleterious to the host organism and may be lethal.
While this is very intriguing, the report/commentary reminded me of another problem I’ve been noticing in the science journalism press, especially these days when we’re all writing and publishing more articles about genetics.
Stock images and illustrations are an important resource both for small newsrooms that can’t hire their own designers and for all newsrooms — including those with designers — lacking the skills to create (even partially accurate) scientific visuals. Articles of science journalism about genetics require such visuals more than others because, while the subjects of these narratives are physical entities, they’re too small to be seen by the naked eye as well as whose visuals as seen through microscopes aren’t particularly visually captivating. Instead, stock images have done the trick.
Pixabay, Getty Images, and other libraries of such assets are choc-a-bloc with 2D and 3D (or 2.5D?) illustrations of the DNA double helix. But I’ve noticed that a great number of them have a common problem — curiously, in a specific way, echoed in the objection the scientists’ group has expressed against “mirror life”: many of these illustrations show the DNA helix twisting to the left. In all our bodies, DNA virtually always twists to the right. That is, the right-handed enantiomer is what animates our bodies whereas the left-handed enantiomer is absent, but which hasn’t stopped it from dominating stock images of DNA.
I realise most people don’t care and/or that the image is captioned to be “for representative use only”. DNA of other configurations, including a left-handed one, exist as well to be fair. And most of all, DNA’s chirality has almost never been the narrative subject. But today it is, as the scientists have so clearly articulated, and the visuals of science journalism need to buck up as well.
