If we could replace DNA, RNA and the ribosomes in our cells by their mirror image versions, then everything would work in the same way, except that the chirality of all molecules would have been inverted. We may be able to do this in a fertilized egg and use artificial incubators where the growing embryo would receive the right nutrients. For example D-glucose must be replaced by L-glucose. To feed the population we must then create the mirror image versions of plants and some bacteria involved in nitrogen fixation.

A population of mirror image people would then be immune to infectious diseases. The question is if this is something we may be able to do in the near future, say within a century.

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    $\begingroup$ I seriously doubt this would work in the long run. Pathogens would evolve quickly to fill the niche and many chiral biomolecules are already known to spontaneously generate racemic mixtures in vivo $\endgroup$ Apr 22 '20 at 9:34
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    $\begingroup$ BTW, I am downvoting because if you'd done some research, you would have easily found that L.Dutch's answer is correct. Or if you'd just thought it through for that matter. $\endgroup$
    – Matthew
    Apr 22 '20 at 13:55
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    $\begingroup$ "We may be able to do this in a fertilized egg": no we wouldn't, unless we assume some sort of very powerful magical technology. Note that if we had that kind of technology we could simply hunt and kill every single undesirable virus, bacteria or mad cell, and thus we would have no incentive to make allostereoisomeric humans. $\endgroup$
    – AlexP
    Apr 22 '20 at 15:54

I think this is almost impossible.

  • you would need to change all the species which we use as food, and all the species which they use as food source, and all the species which they use as food source and so on and so on.. basically every life form on Earth
  • our very life depends on a lot of symbiotic bacteria we host in our organism, mostly the intestine. Sometime those very bacteria end up in the wrong place and cause health problem. See for example Escherichia Coli
  • you would need to also change the organisms responsible for decomposing all the organic materials we dump as byproduct of our processes, including but not limited to sewer waste.

Wrapping up, it would a gigantic task and, due to the last two bullets, it would likely end up in transferring the mutation to harmful bacteria and viruses, since it's known that bacteria exchange genetic material by exchanging plasmids. It would be a matter of time before and old pathogen (or worse a new one) would get the mutation.


To be throughout:

(...) the chirality of all molecules would have been inverted.

It would not, and here is why.

Two examples of these ubiquitous, essential molecules are carbohydrates and amino acids. In all organisms on Earth, most carbohydrates are found in what is known as the D configuration. The "D" stands for "dextrorotatory" but the nomenclature is confusing. For carbohydrates, the configuration is defined as relative to glyceraldehyde, a simple sugar. Thus D-fructose or D-glucose have the same configuration as D-glyceraldehyde, but only D-glyceraldehyde is guaranteed to be dextrorotatory.

Amino acids in life on Earth are predominatly "L", meaning they share an absolute configuration with L-glyceraldehyde.


So humans, like most life on Earth, is made of a mixture of levorotatory and dextrorotatory molecules. Some types of the molecules in humans are predominantly dextrorotatory and some are levorotatory.

Supposing chirality did behave as assumed in the question, it still wouldn't be so simple. The complex molecules that form living being aren't symmetric in only one plane. On top of that, the enantiomerism we learn in high school usually deals with only small molecules that usually have only one stereocenter. A protein may have thousands of stereocenters, and flipping all of them may not be feasible.

For example, this is the human hemoglobin:

Human hemoglobin

Source: https://en.wikipedia.org/wiki/Hemoglobin

It's called "globin" because, looking from afar, the whole molecule may look like a globe. Looking closely you see that it is made of many carbon chains. If you just twist each stereocenter the other way around, they will tend to twist mostly outwards. If a protein still forms, it will tend to be concave instead of convex. It will probably not work as an oxygen transport protein anymore, or less probably it will still work but less efficiently.


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