Mirror life

Many of the essential molecules for life on Earth can exist in two mirror-image forms, referred to as "left-handed" and "right-handed", but living organisms do not use both. Proteins are exclusively composed of left-handed amino acids; RNA and DNA contain only right-handed sugars. This phenomenon is known as homochirality.[8] It is not known whether homochirality emerged before or after life, whether the building blocks of life must have this particular chirality, or indeed whether life needs to be homochiral.[9] Protein chains built from amino acids of mixed chirality tend not to fold or function as catalysts, but mirror-image proteins have been constructed that work the same but on substrates of opposite handedness.[8]

Hypothetically, it is possible to recreate an entire ecosystem from the bottom up, in chiral form. In this way, the creation of an Earth ecosystem without microbial diseases might be possible. In some distant future, mirror life could be employed to create robust, effective and disease-free ecosystems for use on other planets.[10]

Advances in synthetic biology, like synthesizing viruses since 2002, partially synthetic bacteria in 2010, or synthetic ribosomes in 2013, may lead to the possibility of fully synthesizing a living cell from small molecules, where we could use mirror-image versions (enantiomers) of life's building-block molecules, in place of the standard ones. Some proteins have been synthesized in mirror-image versions, including polymerase in 2016.[11]

Reconstructing regular lifeforms in mirror-image form, using the mirror-image (chiral) reflection of their cellular components, could be achieved by substituting left-handed amino acids with right-handed ones, in order to create mirror reflections of all regular proteins. Analogously, we could get reflected sugars, DNA, etc., on which reflected enzymes would work perfectly. Finally we would get a normally functioning mirror reflection of a natural organism - a chiral counterpart organism - with which natural viruses and bacteria couldn't interact. Electromagnetic force (chemistry) is unchanged under such molecular reflection transformation (P-symmetry). There is a small alteration of weak interactions under reflection, which can produce very small corrections, but these corrections are many orders of magnitude lower than thermal noise - almost certainly too tiny to alter any biochemistry. However, there are also theories that weak interactions can have a greater effect on longer nucleic acids or protein chains, resulting in much less efficient conversion of mirror ribozymes or enzymes than normal ribozymes or enzymes.[12]

Chiral animals would need to feed on reflected food, produced by reflected plants. The great advantage, though, is that such chiral organisms should enjoy a disease-free life, completely immune to all viruses and microbes.

Viruses would be completely incompatible with the reflected cellular structures; and bacteria, protozoa, and fungi could not function because they would not be able to find normal sugars inside reflected organisms. The reverse sugars circulating in the chiral organism's body would be indigestible as far as normal bacteria are concerned, so any bacterium entering a chiral organism would simply starve to death. The chiral environment is hostile for normal viruses, protozoa, bacteria, etc.

Mirror life presents potential dangers. For example, a chiral-mirror version of cyanobacteria, which only needs achiral nutrients and light for photosynthesis, could take over Earth's ecosystem due to lack of natural enemies, disturbing the bottom of the food chain by producing mirror versions of the required sugars. Some bacteria can digest L-glucose; exceptions like this would give some rare lifeforms an unanticipated advantage.

Direct application of mirror-chiral organisms can be mass production of enantiomers (mirror-image) of molecules produced by normal life.

• Enantiopure drugs - some pharmaceuticals have known different activity depending on enantiomeric form,
• Aptamers (L-ribonucleic acid aptamers): "That makes mirror-image biochemistry a potentially lucrative business. One company that hopes so is Noxxon Pharma in Berlin. It uses laborious chemical synthesis to make mirror-image forms of short strands of DNA or RNA called aptamers, which bind to therapeutic targets such as proteins in the body to block their activity. The firm has several mirror-aptamer candidates in human trials for diseases including cancer; the idea is that their efficacy might be improved because they aren't degraded by the body's enzymes. A process to replicate mirror-image DNA could offer a much easier route to making the aptamers, says Sven Klussmann, Noxxon Pharma's chief scientific officer."[13]
• L-Glucose, enantiomer of standard glucose, for which tests showed that it tastes likes standard sugar, but not being metabolized the same way. However, it was never marketed due to excessive manufacturing costs.[14] More recent research allows cheap production with high yields, however the authors state that it is not usable as a sweetener due to laxative effects.[15]

The creation of one chiral human is the basis of 1950 Arthur C. Clarke's story "Technical Error", from The Collected Stories. In this story, a physical accident transforms a person into his mirror image, speculatively explained by travel through a fourth physical dimension.

In the 1970 novel "Spock Must Die!" by James Blish, the science officer of the USS Enterprise is replicated in chiral form by a transporter mishap. He locks himself in the sick bay where he is able to synthesize chiral forms of basic nutrients needed for his survival.

An alien machine that reverses chirality, and a blood-symbiote that functions properly only when in one chirality, were central to Roger Zelazny's 1976 novel Doorways in the Sand.

On the titular planet of Sheri S. Tepper’s 1989 novel Grass, some lifeforms have evolved to use the right-handed isomer of alanine.

In the 2014 science fiction novel Cibola Burn by James S. A. Corey, the planet Ilus has indigenous life with partially-mirrored chirality. This renders human colonists unable to digest native flora and fauna, and greatly complicates conventional farming. Consequently, the colonists have to rely upon hydroponic farming and food importation.

In the 2017 Daniel Suarez novel "Change Agent", an antagonist, Otto, nicknamed the "Mirror Man", is revealed to be a genetically-engineered enantiomeric human. He views other humans with disdain and causes them to feel an inexplicable repulsion by his very presence.

• Chemical chirality in popular fiction
• Xenobiology