Symmetry is a familiar property. From a simple vase to common architectural motifs, we’re surrounded by symmetry. The famous detective Hercule Poirot found the need for symmetry so compelling that he chose his London flat on the basis of symmetry. Hercule is not alone: a recent scientific study concluded that "facial symmetry seems to be important in ratings of attractiveness." Indeed, beauty and symmetry are commonly linked. For example, the first entry in Merriam-Webster’s definition of symmetry is: balanced proportions; beauty of form arising from balanced proportions.
Symmetry is also an important concept in math and science. A particular type of symmetry, chiral symmetry, forms the basis of many biological interactions, and thus plays a crucial role in forming the basis of life on earth. Unlike symmetry, the term chiral is not immediately familiar to most people outside of math and science.
So, join me on the flip side for a brief description of chirality!
Although chirality is not a familiar term to most people, the property of chirality is easily recognizable. By definition, an object is chiral if it is not superimposable on its mirror image. Well, that cleared things up, right? Maybe not, so I’ll try to provide a clearer explanation: when you shake hands with someone, why do you both use your right hands? Why don’t you shake their left hand with your right hand? You can try it, but it doesn’t really work. Now take your right hand and try to superimpose it on your left hand. You can’t. Your hands may be mirror images, but they are non-superimposable. And hence your hands are chiral. For this reason, chirality is often called "handedness" and the two hands are known as enantiomers. Likewise, our feet are chiral, which is why most of us don’t wear our left shoe on our right foot. This brings me to another definition: racemic. A racemic mixture is when both enantiomers are present in a 1:1 ratio. For example, the prototypical human has a racemic mixture of hands and feet.
Not everything that is chiral exists as a racemic mixture. Take, for example, biomolecules. Sugars, proteins and DNA are all chiral. Each also exist as only one of two possible enantiomers. How this occurred has implications for the origin of life.
Not surprisingly, molecules that interact with chiral biomolecules are often chiral themselves. Typically, only one enantiomer interacts with a receptor biomolecule (the hand shaking analogy works here – you don’t use your right hand to shake someone else’s left hand). Many of these molecules occur naturally as only one enantiomer. For example, remember those donuts that cause comments to be hidden? Well, they contain cholesterol, which is a chiral molecule with obvious biological activity. Cholesterol exists in nature as one enantiomer. Another recognizable molecule is lactic acid. Also exists as a single enantiomer. In each case, the other enantiomer does not have the same biological effect because it doesn’t interact with the same receptor.
Now this brings up another important point. Just because one enantiomer does not have the desired biological effect doesn’t mean that it won’t have a different biological effect. And sometimes, the effect it does have is quite undesirable. One of the most well-known examples is, of course, thalidomide. I first heard of this drug in the 90s when I saw a feature on 60 Minutes. For those who have not encountered this name before, thalidomide was prescribed for women in the 1950s to counteract morning sickness. One enantiomer is highly effective as an anti-emetic. The other is not. Unfortunately, as it turns out, this enantiomer was not merely an innocent bystander. It is teratogenic. That a drug that causes horrendous birth defects was ever prescribed for pregnant women still renders me speechless.
The realization that one enantiomer can be effective at treating illness, while the other can have disastrous side effects, has generated intense efforts to develop so-called single enantiomer drugs. In fact, the 2001 Nobel Prize in Chemistry was awarded to three individuals who revolutionized ways to make chiral, non-racemic molecules.
Now, in the case of thalidomide, using only the enantiomer that possesses anti-emetic activity wouldn’t have avoided the catastrophic outcome. The molecule racemizes under physiological conditions, meaning that the "bad" enantiomer would be formed in the body even if only the "good" enantiomer were administered. The story is not all bad, though: thalidomide is currently being used to treat multiple myeloma, a type of cancer that affects the immune system. And, there are single enantiomer drugs on the market that aren’t susceptible to racemization and apparently have fewer side effects than the racemic mixture.
I’ve used the example of thalidomide and the increasing prevalence of single enantiomer drugs in today’s world to illustrate the relevance of chirality to everyone’s lives. And there are many other examples of chirality that we encounter on a regular basis. For example, many of us have had rye bread in the not-so-distant past. But how many have had spearmint bread? Sounds disgusting, right? Well, those two flavors arise from different enantiomers of carvone. Likewise, one enantiomer of limonene produces the scent associated with lemons, whereas the other produces the scent of oranges.
I’ve already mentioned that only one enantiomer of lactic acid exists in nature. Many humans have a hard enough time digesting lactic acid as it exists in milk. Imagine, given the profound differences between enantiomers, what would happen if you were to encounter the opposite enantiomer of lactic acid in milk?
Now, if you'll only attend, Kitty, and not talk so much, I'll tell you all my ideas about Looking-glass House. First, there's the room you can see through the glass -- that's just the same as our drawing-room, only the things go the other way. I can see all of it when I get upon a chair -- all but the bit just behind the fireplace. Oh! I do so wish I could see that bit! I want so much to know whether they've a fire in the winter: you never can tell, you' know, unless our fire smokes, and then smoke comes up in that room too -- but that may be only pretence, just to make it look as if they had a fire. Well then, the books are something like our books, only the words go the wrong way; I know that, because I've held up one of our books to the glass, and then they hold up one in the other room.
How would you like to live in Looking-glass House, Kitty? I wonder if they'd give you milk, there? Perhaps Looking-glass milk isn't good to drink...
Alice, clearly, has given this much thought, even though Lewis Carroll’s famous novel was published not long after the discovery of the molecular basis for chirality.
Well, I hope you’ve enjoyed reading! Be sure to help me celebrate my first diary!
For additional fun, I recommend that you play the chirality game!
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On to Top Comments!
From the inbox, topcomments at gmail dot com
From kath25:
clonecone's response to GoldnI's recipe in RealityBias' diary was hysterical.
From Turkana:
kath25 takes me down the rabbit hole. {Heh - pop!}
From Asimbagirl:
I don't think that my sentiments could be more aptly captured. This comment is right on the money!
From creeper:
I'd like to submit this comment from godsbodkin. The questions it asks about us and our society need to be considered by every American.
From madgranny:
Bob Altemeyer in the diary discussing his book gives a thoughtful comment on the Republican candidates. {I couldn't agree more - this is a must read comment, imo.}
From Carolita:
jct makes an insightful and inspiring comment in sangemon's Peace Train Sounding Louder.
duha explains why anyone who bought shrub's reasons for invading Iraq is TOO DUMB TO BE PRESIDENT in goldberry's Bubba, don't look as us in that tone of voice.
Halcyon and calipygian bring important points to the discussion in Jeff Huber's Pat Tillman and the Size of the Lie.
From homerun:
Joan in Seattle had a great response to this comment.
From Cronesense:
Diary: 95%of Rove's emails from RNC servers=The Endgame By: BloggerJohn
Patriot4peace makes an important point to counter the administration's Jekyll/Hyde approach to 'privacy'!
noweasels, our very own legal-beagle, makes some fine legal distinctions for us. Follow the thread for her continued explanations of the law.
The Big Red One has a tidy,annotated to-do list.
davybaby has an interesting tidbit of info that shows the long held belief the GWB doesn't know how to email is a fallacy.
one pissed off democrat has some very intriguing tech information in bold in this comment. Could be a real Gotcha!
From gloriana:
Bob Altemeyer and John Dean visited dKos today to discuss Altemeyer's online book The Authoriarians. The entire comment thread is well worth the read, but here are some to whet your appetite:
bob altemeyer with good news regarding America's dropping away from authoritarian values. Another, a long one, regarding the role authoritarianism will play in the 2008 presidential run {Not surprisingly, this one got more than one rec!}
jwdmkd (Mr. Dean) regarding Republican Senators in jeopardy
And from emeraldmaiden:
In Ticia's diary,Power Abuse: Lessons from Women anna shane's comment reallystood out to me.
Pickle's picks:
I was just in awe of the participation of Bob Altemeyer and John Dean in abbeysbook's diary The Authoritarians Meet Altemeyer&John Dean Today.
John Dean's comment gives me further reason to be wary of Blue Dog Dems.
Bob Altemeyer responds to Abraham Running For Congress When I Turn 25's question about how people don't see proto-fascism. I wonder what Abraham plans to do with his life?
skrymir's take on a comment from Dr. Bob sums up how I feel.
Gooserock explains what we're up against in Cenk Ugyur's diary The Republican Party vs. George Bush.
marykk has a great suggestion for Canadian Bill in the latest installment of Back to the Land.
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Top Comments by Mojo:
Without obvious tip jars, C&J, and first comments:
1 At the very least by emptywheel - 184
2 I hear he knows some prominent bloggers here by David Boyle - 163
3 wait just one friggin' minute by Patriot4peace - 134
4 Thank you by Persiflage - 100
5 gwb43.com by BloggerJohn - 87
6 Rove sent e-mails by noweasels - 87
7 The Edwards health plan is not perfect . . . by nyceve - 85
8 Yes. I believe that can often be the case. by slksfca - 83
9 gwb43.com recently targeted in Ohio 2004 vote by Theghostofkarlafayetucker - 76
10 Marcy, Marcy Me by Gooserock - 75
11 Stop the MSM media distortion now by nyceve - 70
12 J. Dean checking in... by jwdmkd - 66
13 Prob'ly hint by David Boyle - 65
14 Easy answer to complex questions by funluvn1 - 65
15 For example by MarkInSanFran - 63
16 Bob here by bob altemeyer - 62
17 I don't understand why we're still waiting. by zic - 60
18 No FP tonight, but Spooky and I are by blue jersey mom - 59
19 Ditto here by CTLiberal - 57
20 Keep Bush in the crosshairs by Dallasdoc - 56
21 MFP by sobermom - 55
22 Illegal by MarkInSanFran - 54
23 "oznick" had a diary the other day, graphing the by Theghostofkarlafayetucker - 51
24 MFP: Everything by vigilant meerkat - 51
25 As I type this, an old friend by Dreaming of Better Days - 50
26 You're so by taylormattd - 47
27 And you can bet... by Dem In VA - 46
28 My FPs by edwardssl - 46
29 Time to get a court order to raid the... by xynz - 45
30 sdfg by bonddad - 45
With everything:
1 Tip jar by occams hatchet - 385
2 Tips by Cenk Uygur - 232
3 Does Fitz read dKos by litigatormom - 216
4 At the very least by emptywheel - 184
5 I hear he knows some prominent bloggers here by David Boyle - 163
6 Just don't accuse me of fear-mongering by citizen92 - 145
7 wait just one friggin' minute by Patriot4peace - 134
8 Well, well, well by MarkInSanFran - 113
9 Thank you by Persiflage - 100
10 Tips for the animals by zeke7237 - 89
11 A month ago by plf515 - 88
12 Rove sent e-mails by noweasels - 87
13 gwb43.com by BloggerJohn - 87
14 The Edwards health plan is not perfect . . . by nyceve - 85
15 The really sad thing is by dmsilev - 84
16 Yes. I believe that can often be the case. by slksfca - 83
17 gwb43.com recently targeted in Ohio 2004 vote by Theghostofkarlafayetucker - 76
18 Marcy, Marcy Me by Gooserock - 75
19 Really good diary, persiflage . . . by nyceve - 73
20 we CAN do better by buhdydharma - 70
21 Stop the MSM media distortion now by nyceve - 70
22 Good morning everyone by Frankenoid - 69
23 Please add all that I missed by abbeysbooks - 69
24 Tip Jar by Jeff Huber - 66
25 J. Dean checking in... by jwdmkd - 66
26 Prob'ly hint by David Boyle - 65
27 Easy answer to complex questions by funluvn1 - 65
28 Your turn..... by CanadianBill - 64
29 For example by MarkInSanFran - 63
30 Diary title worthy of The Onion! by anotherCt Dem - 62
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If you find a notable comment during the day, send it into topcomments at gmail dot com for inclusion! And remember to include your screenname, so we can credit you!