The origin of a prefered enantiomer in the universe?

[teonanacatl]

The thread on free will and particles reminded me of a discussion we had one night.

Curiously there is certianly alot of enantioselectivity present in the universe today, where did it first arise? The probability of synthesising or forming either enantiomer is equal unless an element of enantioselectivity if present.

We are composed mainly of L-amino acids, so at some point L was chosen over D, why? there would had to have been an excess of L amino acids. But where from? Perhaps a chiral surface, but what influenced the chirality of the surface?

The earth spins one way why not the other? Because it had to choose, couldnt spin both and its a 50:50 chance so it just picked one? or rather somthing influenced it to spin one way at some time?

Hmmm, can the universe exist with only 50:50 probability? ie if the probability of the earth spinning either way was exactly 50:50 how would it pick, could it even pick or would it colapse?

When the first chiral molecule formed, however it formed but solong as it was formed free of any chiral influence, it would have had to choose R or S, but presumably this first molecule wouldnt be enough to influence the rest of the universe because the next one to form should be the opposite chirality. It would imply that in the time between the formation (and possible decomposition) of the R isomer and the S isomer one molecule was able to influence the chirality of the universe in a significant mannor. I dont likeit.

Best possible explantation i heard was to do with earths magnetic field.

I dislike probability in most of the ways it is used in normal life, like 1/1000 chance of being eaten by a shark etc because anything is possible and you certainly effect your chances by making specific choices in certain senarios, ie using your apparent free will. So without free will though probability makes more sense to me, nothing to alter the odds even 0.00000001%.

[devance]

http://en.wikipedia.org/wiki/Enantiomer

Apparently alot of worry on the subject.

Since theres a maththematical direction who cares.

Since we exist.

Entropy is a worry for physicist but not philosophers.

[nabraxas]

Apparently alot of worry on the subject.

i don't see any worry on wiki at all??

Since theres a maththematical direction who cares.

Since we exist.

Entropy is a worry for physicist but not philosophers.

And nothing worries those who know that God made the earth in seven days & that these are the last days...

The earth spins one way why not the other?

well Venus and Uranus & some planets moons spin the opposite way, so there are some discrepancies, but other than that i got nothing.

Edited August 24, 2008 by nabraxas

[devance]

I got nothing either.

but Nasa is a good fact gatherer.

the human eye for looking as space.

Should be left alone and not politically influenced or starved of funding.

http://answers.yahoo.com/question/index?qi...24134525AAhIiet

[blizznshot]

This doesn't really get at the WHY L-amino acids over D, but I read this pretty cool biophysics paper in which the HIV protease was synthetically manufactured entirely out of D amino acids. After being refolded in-vitro, activity assays were performed. Not surprisingly, its activity was confined to a substrate that was also synthesized out of D amino acids (same sequence as the normal substrate, just different enantiomers). Km and Kcat values were identical.

As for the question of why L over D, I suspect it has to do with the chance structure of the first ribozymes (RNA "enzymes" from primordial "RNA World). Simply speaking, the first peptidyl transferase turned out to have a structure that favored L. After that, it's a downard spiral...

[apothecary]

Best topic in this subforum, ever.

Stereochemistry is some fucked up physics which has intruiged me forever (come up with the stereoisomer of sugar and you'd be a billionaire), but who knows how it all got started.

Funnily enough, of all the explanations for the planet, between God and cold hard science, I would pick any of them over statistics. But statistics really does seem like the most probable answer, excuse the pun.

[teonanacatl]

Blizz you forget that ribozymes are proteins made of amino acids!!! And DNA is chiral too so it would all have to come well before either of those.

My best guesses are polarised light, or magnetic field effects but neither still is the beggining of the asymmetry.

Curious to your comment sina re stereoisomers of sugar, explain

[apothecary]

I heard if you could easily synthesise the stereoisomer of sugar, you would have a sweet tasting sugar substitute that your body simply doesn't process. i.e no health consequences.

Edited August 26, 2008 by Sina

[teonanacatl]

hmm I reckon its already been done, you can buy the other enantiomers of both glucose and fructose so Im sure you could make sucrose. infact some L sugars are already sold as artificial sweetners :D

[apothecary]

Sure, I'm not saying it's impossible to synthesise teo, just that for it to work commercially you need to figure out how to make it cost pretty much the same as sugar.

Any links on those stereoisomers you can buy? I couldn't find anything but I'm feelin lazy tonight anyway. So is what I heard true? Does the stereoisomer for these sugars really pass through the body with no health issues?

[teonanacatl]

L-glucose

http://www.sigmaaldrich.com/catalog/search...ail/SIGMA/G5500

Yeah L-glucose cannot be metabolised by glycolysis, not sure on any other effects however it is basically physiologically inert. The thing is it may not be sweet. Carvone is a great example of how changing the stereochemistry can change smell, same could occur with taste. S-carvone smells like caraway,R-carvone smells like spearmint. So yeah it might not be as sweet as D-glucose.

[blizznshot]

Blizz you forget that ribozymes are proteins made of amino acids!!! And DNA is chiral too so it would all have to come well before either of those.

Ribozymes are not proteins. They are catalytic RNA molecules, such as those found in the splicesome and ribosome. They are often found in a complex with proteins, but can also be found free-standing.

The long and short of what I'm getting at is that life almost certainly began in an "RNA World." The first self-replicating molecules were RNA. Eventually, these RNA molecules gained a peptidyl-transferase function (linking amino acids). It was the structure of these peptidyl transferase RNA molecules that caused them to prefer the L-enantiomer as a substrate. It was arguably a chance structure, and thusly a chance event.

To this day, the peptidyl transferase active site of ribosomes is composed entirely of rRNA!

As a side-note, DNA likely came last (in terms of its role in biology). The main reason for this is that it lacks a 2' hydroxyl, which makes it less interesting in terms of chemistry/configuration (and less likely to have participated in primordial molecular evolution), but more stable. Hence, DNA was ultimately used for information storage.

Edited August 27, 2008 by blizznshot

[Undergrounder]

i don't know what you chemistry heads are on about, but if you like thinking about things existing as probabilities, that's one interpretation of exactly how things actually exist... ie: a particle isn't 'spin up' or 'spin down', its 50:50 until it gets measured, at which point it collapses into one form or the other..

and about why the world spins one way and not the other, this was an argument Leibniz used against Newton's version of absolute space and time. If space is absolute, Leibniz wanted to know why God (or any other thing) created the universe in the point it is, and not say.. 50 miles to the East. The law of sufficient reason (in a deterministic universe) states that every effect must have a cause, and the idea of the universe as absolute and not relative broke this law... of course Leibniz was right, and Einsten later proved him right. Another victory for Leibniz as the greatest genius of all time.

But i don't know exactly why the earth does spin the way it does (do all the planets spin the same way??) but i kind of imagine a big meteorite smashing into it and setting it off in that direction, more so than the combined effect of other particles smashing into it in the opposite direction over the years... but i don't know there's probably a more elegant physical reason for it or something...

[teonanacatl]

ahh thanks blizz :D never knew that, however they contain a pentosephosphodiester backbone yeah and so would require one enantiomer of sugar.

Was talking to a mate about it, i think we are looking at it wrong, enantiomers arnt actually exact opposites, the true opposite config would be the antimatter version of the compound yeah?

Apparently and i cannot confirm this but enantiomers can have differeing solubilities in otho and para water.

[FancyPants]

Perhaps it's just our perception of the direction of side/spin/direction. A clock ticks clockwise, if we were looking at the clock from behind (or reverso) then the clock EDIT: sorry the "hand" would be moving ANTI-clockwise.

The world rotates west to east because we are looking at the Earth at the aspect of northern hemisphere to the north; what happens when we look at the globe from upside down?

I dunno.

Edited September 17, 2008 by FancyPants

[ThunderIdeal]

yeah, we talk about things like 'spin', but it's just a concept. easy to believe that scientists can see what's actually happening but, (feel free to inform me otherwise) they don't really. spin is part of a scientific model which may be deceptively false.

ahhh, CERN discoveries are gonna be really interesting. everyone be sure to post any articles you come across.