Top Posts Tagged with #homochirality

a bit about chirality

one of my personal favourite things in science is chirality. for those that haven't heard of it, it's basically the idea that a something's mirror image is not the same as the original shape. it can be a bit confusing - try using your hands to visualise it. with both your palms facing the same way, they are mirror images, but if you rotate one of your hands it doesn't become the same shape as the other at any point. therefore, your hands are chiral. consequently, things whose mirror image can be superimposed onto the original are achiral.

if this is still tough to get your head around, i recommend taking a look at this website:

An object can either be chiral or achiral. Achiral objects are identical to their mirror image. Chiral objects are not. Chiral objects are

in the science world, this concept is really important. everything in life is chiral - known as homochirality - and it exhibits both 'left-handedness' and 'right-handedness'; animo acids and proteins are left-handed, and DNA, RNA, and their "building blocks" are right-handed (which is why DNA spirals to the right).

chirality exists in compounds and substances as well, and here's where the concept comes into play.

our bodies and medicines have evolved to recognise and target compounds, bacteria, viruses, et cetera, but all of these have a specific 'handedness' that we have grown accustomed to. therefore, our bodies are essentially ineffective against mirror versions of these things that we otherwise see on a day to day basis.

in pharmaceuticals, this has the potential to be groundbreaking. as our medicine evolves, so do viruses and bacteria, but if we were to make a 'mirror' medicine, its targets would have very little defense against it. this could slow down bacteria's and viruses' evolution against medicines and, with a lot of work, could even be the demise of some infections as a whole. adding onto that, medicines could have an improved effect on us; as our immune systems only recognise a specific handedess, mirror medicines could last for longer and be safer than current ones.

however, there is also the potential that mirror bacteria (as one example) could come to exist as well. bacteria have 'fingerprints', of sorts. when a foreign substance enters our bodies, defenses that we've built up help us to recognise and destroy anything harmful because of its fingerprint.

were a mirror bacteria to invade an animal or plant, it could be unable to inflict pathogenic effects on the host's immune system because of 'mismatched chirality'. woohoo!

however, as there is so little research into actual effects of mirror bacteria -partially because we aren't able to create even normal life synthetically yet, and partly because of risks that will be mentioned very shortly - they could act as a cancer, using up necessary things in the host's body like nutrients and physical space.

sounds great. and it only gets better!

there is also the chance that if one of these mirror bacterium was to infect someone, it could be allowed to spread with very little, if any, resistance (as our immune systems are primed to defend against specific handedness-es).

do you see how this could be an issue with contagious illnesses?

thus, there is the possibility that - were mirror bacteria or other forms of mirror life to be created - our crops, livestock, wildlife, nature, and even humans, could be completely wiped out.

even though this is possibly one of the most interesting concepts in science, and could solve many problems with infections and illnesses globally, the risk is literally unprecedented. luckily, there are boundaries in place to ensure our safety. while we are barely scratching the surface of even creating synthetic life in the first place - and it will take a lot of scientific innovation before creating mirror life is even an option - there are ongoing global discussions about limitations on the area that research into the topic should be allowed to spread.

( i can't find any official names or documents of government restrictions, likely due to the fact that it's still a conversation that governments are having, but scientists around the world have agreed that experimentation with mirror life should have strict guidelines. the uk's office for science in the government states that "a clear distinction should be made between research to develop mirror components (individual molecules such as peptides and enzymes) and mirror organisms or cells (or any biological unit capable of self-replication), even though both are sometimes termed 'mirror life'.", but there's little information on the actual guidelines.)

anyways, thanks for listening to my ted talk. i'm a bit of a science nerd and this is by far one of my favourite subjects of discussion. feel free to ask me questions or request another topic for me to discuss!

Citations:

Service, R. (2023) ‘breakthrough’ could explain why life molecules are left- or right-handed | science | AAAS. Available at: https://www.science.org/content/article/breakthrough-could-explain-why-life-molecules-are-left-or-right-handed (Accessed: 07 February 2026).

Sample, I. (2024) ‘unprecedented risk’ to life on earth: Scientists call for halt on ‘mirror life’ microbe research, The Guardian. Available at: https://www.theguardian.com/science/2024/dec/12/unprecedented-risk-to-life-on-earth-scientists-call-for-halt-on-mirror-life-microbe-research (Accessed: 07 February 2026).

Unknown (2025) Mirror life, GOV.UK. Available at: https://www.gov.uk/government/publications/mirror-life/mirror-life#key-points (Accessed: 07 February 2026).

#chirality #homochirality #science #biology #chemistry #pharmaceutical #mirror life #science side of tumblr #stem #stemblr

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How did homochirality come to be on Earth? It is one of many open questions in science, and this new finding could help scientists figure it out. We now may be able to determine whether molecules get skewed in one direction while they're first forming in space, or later on when life starts to arise.

#space #science #chemistry #homochiral #homochirality #open question #unanswered questions #Unknown #Known Unknowns #unsolved problem #reversopedia #lygometry

the (now experimentally supported) Vester-Ulbricht hypothesis is that the chirality of biologically important molecules (i.e. the fact that sugars and amino acids are all "left-handed") is ultimately due to the fact that cosmic beta rays (electrons produced by the weak interaction during nuclear decay) are exclusively left-handed - so the biological parity violation is a consequence of the fundamental physical parity violation

#science #biology #homochirality #vester-ulbricht hypothesis #weak interaction #parity violation #physics #chemistry #own #text

It’s Not Just Our Tooth That’s Sweet

Biology concepts – homochirality, carbohydrates, chiral discrimination, glycoside, H antigen

It isn’t just biomolecules that show chirality. There is also

chiromorphology, like snail shells that usually turn to the right

(dextral, or D-). There are factors in early embryonic

development that cause the body and shell to be right handed

in most gastropod species, yet other species are left handed.

There are also instances where a right-handed species will

produce a left-handed individual, so shell collectors have to be

on the look out for abnormal individuals.

A couple of weeks ago we talked about how, in most cases, life uses exclusively the left-handed enantiomers of amino acids to make proteins. This homochirality is also see in the sugars we talked about last week, but in this case, mostly D-sugars are utilized in biological systems.

What isn’t amazing is that it happens to be L- for amino acids and D- for carbohydrates; the fact that they’re different is no big deal. Evolution just wants the parts to fit together, so if an enzyme evolved to use D-sugars, it’s not a surprise that the D-sugar would be favored in the pathway then now on.

But it might not have been random either. No one knows for sure, but hypotheses abound for how homochirality in these biomolecular monomers was established.

One 2009 paper was concerned with the maintenance of homochirality rather than its establishment. Dr. Soren Toxvaerd stated that if you don’t believe life as we see it today occurred in a singular event, then it must have developed over a long period of time. Evidence indicates that small changes in the self-assembly of biomolecules took place over at least thousands of years.

If life took a long time to develop, then prebiotic (before life) earth must have been fairly stable in terms of enantiomer concentrations. But we know that homochiral solutions will turn to racemic mixtures (containing both L- and D- enantiomers) in a short time, days for amino acids and just hours for sugars. So how could the environment have been stable enough for life to develop over time?

One possible hypothesis about the establishment of homochirality

was put forth in 2010 by Koji Tamura, PhD in the Journal of

Cosmology. Put very simply, RNA may have developed before

proteins. RNA evolved to use only D-ribose because a mixture

would have been a symmetry violation. The action of D-ribose

would have been driven toward L-amino acids because of shape

problems with attaching D-amino acids to tRNAs. Now prove it.

Louis Pasteur, he of bacteria-free milk and germ theory, may have shown us the way. He discovered chiral discrimination. Racemic mixtures, under the right conditions, will separate into pools of homochirality. There is an energy gain and stability to packing homochiral molecules together; the other enantiomer will be excluded. This could help explain life using one enantiomer only.

What is more, hydrothermal vents and black smokers have just the needed conditions for both chiral discrimination and for self-assembly of biomolecules. Interesting huh? Think it’s a coincidence that black smokers harbor some of the oldest archaea on Earth? We may owe our very existence to plumes of superheated water and the xenophobia of enantiomers.

Lastly in this area, it may be that sugars and amino acids selected each other for homochirality. Glyceraldehyde is 1) highly discriminate for its enantiomers, 2) was present in large amounts in prebiotic oceans, 3) is used in self-assembly of many biomolecules, and 4) D-glyceraldehyde very much likes to bind to L-serine. So a slight excess in either one of these could have helped select for the other, and if this was stable, it could have caught on like “Gangnam Style.” This may be why life uses mostly D-sugars and L-amino acids and why I know the name Psy.

Now that we have delved into the mire that is maintenance of homochirality in sugars, let’s look at the rule breakers. D-sugars aren’t the only game in town.

Bacteria, oh bacteria! Once again, they lead the way in rule breaking. Last week we discussed how E.coli can generate ATP from several different sugars - glucose, lactose, etc. It takes different enzymes to metabolize each sugar, so if they are going to invest the energy in maintaining those genes and making those enzymes, there better be a good reason.

Paracoccus species 43P has been shown to have an L-glucose

metabolic pathway. This organisms is very closely related to

Paracoccus denitrificans. P. denitrificans is believed to be the

organism that was engulfed to become the eukaryotic

mitochondrion. It closely resembles the mitochondrion, and

although random genes needed for aerobic respiration have

been found in many prokaryotes, P. denitrificans is the only

prokaryote in which all the necessary genes have been found.

A 2012 study tried growing soil bacteria on medium that contained only L-glucose as an energy source. One species of bacterium, Paracoccussp. 43P, was able to metabolize L-glucose to pyruvate and glyceraldehyde-3-P, and then make use that for ATP production. The researchers discovered an L-glucose-specific dehydrogenase enzyme, and this enzyme was active in the fluids from broken up paracoccus cells. The process is similar to one in E. coli, but here it is L-glucose specific.

Mammals can’t manage as well as some bacteria; we can’t metabolize L-glucose at all. However, that doesn’t mean it can't work for us. L-glucose has been proposed as an artificial sweetener, especially for type II diabetics. One form of L-glucose can stimulate insulin release, so this would be doubly good for type II diabetics. Unfortunately, L-glucose costs 50% more than gold; therefore, don't look for it next to the Truvia anytime soon.

One, but only one, study has been published showing rats metabolized L-fructose and L-gulose, but not L-glucose. From 1995, the authors waited until the end of the paper to explain that the metabolism was being carried out by the rodents gut bacteria, not by the rats themselves. No wonder it was only one paper.

Just because we can’t metabolize L-sugars doesn’t mean that we mammals are left out in the cold. Some sugars are used in the L-form even if they aren’t broken down to make ATP. The most egregious example of this is a hexose sugar called L-altrose. Why is it different than some other exceptions here? Because altrose doesn’t even occur in nature as a D-sugar; only the L-form has ever been found. It was first isolated in 1987 from a bacterium called, Butyrvibrio fibrisolvens, which is found in the GI tract of ruminate animals (cows and such).

Ruminants are mammals that have more involved digestive

strategies. Ruminants have many types of GI bacteria to help

them break down tough plant material; it isn’t surprising that

some of them can use nonstandard carbohydrates in their

physiology. “Ruminating” is the act of re-chewing food that

has been partially softened by bacterial action in the first

compartment of the stomach, and then brought back to the

mouth as “cud.” I ruminate on ideas all the time, but I think I

will stop – I’m going to call it “further thought” from now on.

Ruminates go the extra mile. They digest longer and work on food harder, using bacteria to help with much of the work. Therefore, it isn’t strange to note that L-altrose has also been seen in another ruminate bacterium, Yersinia enterolitica. Remember though, this altrose isn’t being used in energy production; it's found in their outer cell wall glycoprotein, LPS (lipopolysaccharide).

It turns out that L-sugars are common in bacterial LPS. I found examples from several different bugs, including L-quinvose (6-deoxy-L- glucose), L-rhamnose, and L-fucose (6-deoxy–L- galactose).

When it comes to L-sugars, plants can get into the act as well. Rhamnose (6-deoxy-L-mannose) occurs in nature, and can be isolated from several plants of the genera Rhamnus and Uncaria, including Buckthorn, poison sumac, and many other plants.

Rhamnose from plants takes the form of a glycoside. There’s there word again, glyco-. A glycoside in general terms is any molecule bound to a sugar. In plants, attaching sugars to create glycosides is a common way to inactivate molecules so that they can be stored for later use. When needed, the sugar residues of glycosides are cleaved away by special enzymes and then the protein, enzyme, lipid, etc. becomes active.

Digoxin (or sometimes digitalis) are cardiac glycosides from

foxglove plants. They are used to treat atrial rhythm or heart

failure problems. First used by William Withering in 1785,

digitalis is said to be the first of the modern day therapeutics.

But it can kill you too, both the plants and the drugs. A nurse

was sentenced to 18 life sentences after he was convicted of

killing more than 40 patients with digoxin.

Glycosides can be differentially regulated because there are many sugars that can be used, and several different possible linkages for each sugar/substrate combination. Therefore, cells can precisely control just when and where the glycosides are activated. This may allow cells to function for longer periods of time, but isn’t the reason that rhamnose and fucose (both L-sugars) are being included in obscenely expensive anti-aging creams.

Some evidence suggests that rhmanose and fucose can inhibit the activation of the elastase enzyme in skin cells. Elastase is known to increase in expression and activity as skin cells in culture divide several times. Therefore, companies want you to believe that rhamnose will keep your skin from looking old. Forget that keratinocytes in a petri dish bear as much resemblance to your skin as Watchmen does to Hamlet.

That was a bit sarcastic, but the cosmetic industry is a pet peeve of mine. And while I’m exposing my soul, I might as well admit to being a bit of a speciesist. I like the exceptions best when they involve Homo sapiens, so the last exception for today has to do with our own uses for a deoxy-L-sugar, fucose. I must admit that several uses of fucose apply to many mammals, but being the speciesist that you know I am, I ignore them to focus on humans.

Fucose (6-deoxy–L-galactose) is crucial for the turning of an unloved spermatozoa and a lonely oocyte into very premature teenager. Both the development and maturation of gamete cells and the development of the embryo depend on the recognition and communication of surface molecules that include fucose. But wait, there’s more.

The H antigen is linked to the red blood cell through a fucose

residue, but not in the “h” antigen mutant. Because of this, it

is not recognized for modification to the A or B antigen, and

the typical H antigen is not there to prevent development of

the H antibody.

Fucose is also a component of many glycans, including substance H. Also called the H antigen, this molecule is a precursor to the A and B antigens found on red blood cells. For people with A, B, or AB blood, the H antigen is modified to become the mature A or B antigen, but in people with O blood, the H antigen doesn’t mature and remains an H. Therefore, principal factors in every human’s development and physiology are determined in part by a sugar that we shouldn’t be using – according to the rules anyway.

However, not all is goodness and light when it comes to fucose. Some folks have a mutation in their H antigen gene that prevents its maturation to the A or B antigen. All cells would have the mutant H antigen, called h. This is different from being type O (meaning not having any A or B antigen, but still having the H antigen).

The hh or Oh blood type is called the Bombay type, and is very rare. Bombay individuals can donate blood to anyone, regardless of blood type (because they do not express any antigen to be attacked). However, because they make A, B, and H antibodies, they can receive blood only from another person with Bombay blood type. Since Bombay occurs about three times in a million births – good luck with that search for blood.

Let’s tackle the nucleic acids and their exceptions starting next week. By training I am a molecular biologist; I know an exceptional number of nucleic acid exceptions.

Shimizu T, Takaya N, & Nakamura A (2012). An L-glucose catabolic pathway in Paracoccus species 43P. The Journal of biological chemistry, 287 (48), 40448-56 PMID: 23038265

Toxvaerd S (2009). Origin of homochirality in biosystems. International journal of molecular sciences, 10 (3), 1290-9 PMID: 19399249

For more information or classroom activities, see:

Bombay blood type –

http://www.brighthub.com/science/genetics/articles/34637.aspx

http://www.youtube.com/watch?v=i5C5U8oYcHA

http://anthro.palomar.edu/blood/Bombay_pheno.htm

http://www.slideshare.net/PraveenNagula/bombay-blood-group

http://www.thinkfoundation.org/kc_bombay_blood_groups.htm

http://articles.timesofindia.indiatimes.com/2010-06-14/bangalore/28296209_1_bombay-blood-group-voluntary-donors-world-blood-donor-day

Glycosides –

http://www.friedli.com/herbs/phytochem/glycosides.html

http://www.nutriology.com/glycoside.html

http://www.slideshare.net/MrSyedAmmar/saponin-glycosides

http://www.life.illinois.edu/ib/425/lecture24.html

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=37&ved=0CEgQFjAGOB4&url=http%3A%2F%2Fpollen.utulsa.edu%2FMedical%2520Botany%2Fglycosides.ppt&ei=AzIJUtzcIcf4yAHN_YCIAQ&usg=AFQjCNF-4CagvaFEEl6GWgvsQovlsXpqaA&sig2=aTIuJ7Vho69FR4g_zqyI5A&bvm=bv.50500085,d.aWc

Racemization –

http://pubs.acs.org/subscribe/archive/tcaw/10/i02/html/02brignole.html

http://www.youtube.com/watch?v=g0qZ6BDRsZI

http://journalofcosmology.com/SearchForLife108.html

#red blood cell types #racemic mixture #homochirality #glycoside #exception #chiral discrimination #carbohydrate #Bombay blood type