apps with inverted helices

After my recent blog post on DNA double helices that twist the wrong way (inverted helices), a reader (who prefers to remain anonymous) submitted a few examples of apps featuring such mirror-world DNA. Following the example set in that previous post, I'm showing the corrected versions here:

I'm sure you can still read the text to work out who the culprits were ...

the curse of the inverted helix

I've now figured out what to do with DNA double helices of the wrong chirality, which I frequently see in print and online. Earlier I started compiling a hall of shame, but that might reinforce the wrong image (eg by adding to the already considerable proportion of wrong helices that show up in google searches for double helix).

Instead, I'm now going to flip the images that also contain text, such that the DNA will be the right way round and the text will be mirrored. This way, I can signal-boost the correct structure while also exposing the error.

So, for example, a poster I received yesterday now looks like this:

much better, huh?

The same treatment for the historic blunders of Nature and Science yields:

the inverted helix

It is a fact widely ignored by people who design covers for science books and journals, but let me say it loud and clear, the normal version of the DNA double helix is RIGHT-HANDED, i.e. it is like an ordinary screw in that if you look down the axis and follow the ridge clockwise, the movement will lead away from you (see this example from the Ashmolean Museum's collection of glassware).

If, however, you take a picture of a DNA double helix and mirror it, you end up with something blatantly WRONG like the examples below:







PS in order to inject some scientific method into my rant, I've just done a Google image search for "DNA" and checked the first 30 double helix images shown. Giving those where the chirality isn't easy to see the benefit of the doubt, I have spotted three images with left-handed helices, so the error rate seems to be around 10%, even on websites that get high PageRank.

reflections on chirality

In my occasional series on all things chiral, here's a racemic boathouse:



Just to confuse people, they have put a right-handed staircase (i.e. like an ordinary screw it moves forward if you turn clockwise) on the left of the building, and a left-handed one on the right. If the reflection in the water had been clear enough, you would see a left-handed reflection on the left and a right handed one on the right.

This is one (or maybe two?) of the college boathouses lined up along the river Thames, between the two main channels of the river Cherwell. There is another one next door to this built to the same design.


I also added six other new Oxford photos to my flickr photostream today.

reflections on symmetry

My review of the book

Mirror-image asymmetry: An introduction to the origin and consequences of chirality
by James P Riehl

appears in today's issue (No 14) of Chemistry & Industry, pp28-29.

Here's a snippet:

I was intrigued to learn that the historic Dutch windmills, like so many other things, owe their unanimous chirality to the fact that they were designed for right-handers. Conversely, the plane of the Wright brothers is achiral, as it has two propellers that are mirror-images of each other.
All in all this is a laudable effort by a long-serving practitioner of science to popularise his field, and a book that can enlighten chemists and lay people alike.

The review should show up here soon.



A traditional Dutch windmill (1100 Roe) standing in a winter landscape on the outskirts of Amsterdam, the Netherlands.
Photo by Massimo Catarinella, from Wikimedia Commons.


PS solution to the windmill conundrum: operating the windmill involves climbing up the blades and unfolding the sails. All Dutch windmills are built such that you can do that with your right hand.

a racemate of giant lollies

This blog needs an infusion of colour, so I took a snap of the sweets on display at Mr. Simm's Olde Sweet Shoppe on the high street:



Scientists may enjoy spotting the chirality of the helical lollies in the back row - there are actually a few right-handed helices among a majority of left-handed ones. Which is kind of surprising as one would expect that the machine that makes these things would always turn in the same direction.

reasons for asymmetry

There have been several books recently on the quest for reasons why life is made up of D sugars and L amino acids and ignores the mirror image versions of these molecules, which are identical by chemical and physical criteria. While it is clear that biomolecular systems work better if they only use one of the mirror image versions, it is far from clear which symmetry-breaking event allowed chiral life to arise and prosper in a mostly achiral world.

My review of the book

The origin of chirality in the molecules of life
By Albert Guijarro and Miguel Yus
RSC Publishing 2009
ISBN 978-0-85404-156-5

has now appeared in Chemistry & Industry, issue 9, p. 30. Here's a snippet:

Albert Guijarro and Miguel Yus describe the chirality problem and our current best guesses at its solution very systematically in their book. They start from first principles with the physics of time and space and precise physical definitions of symmetry and asymmetry. They very usefully split the problem into two fundamental aspects: symmetry-breaking events, and mechanisms that could amplify existing imbalance between enantiomers.

Readers who aren't very good at (or keen on) theoretical physics may find

Uwe Meierhenrich: Amino Acids and the Asymmetry of Life: Caught in the Act of Formation, Springer 2008

a bit more accessible.

the importance of being chiral

chiral catalysis is a topic I like to come back to from time to time, and just now my excuse for rambling on about enantiomers is a book review:

Gross M:
Chemistry & Industry No 5 (10.3.),
Not a mirror image (review of "Asymmetric synthesis: the essentials" by M. Christmann, S. Bräse, eds.)

This is a rather dense and difficult monograph though. I'm sure there must be several pop science books on the importance of being chiral, but right now I can't remember any. (except for one written in German, by Henri Brunner, who used to be my inorganic chemistry prof, way back when).

hm. maybe I should put that on my shortlist of potential book projects.