## Posts Tagged ‘chirality’

### Life’s Handedness

November 11, 2008

Origin of life research is a facinating subject, but one of its most baffling findings is that all life that we know of on this planet has a certain chemical “handedness” or chirality.  Well there is some new research that shows why evolution might prefer a certain handedness: certain reactions are more effecient depending on the handedness of the chemicals.

UPDATE: An insightful comment brought up the fact that chirality is an important subject in physics as well.  It turns out this is a useful concept throughout the sciences (maybe because of its relationship to symmetry.)   Here’s some more detailed information I found online, as we go from concrete to abstract:

Biology – Amino Acids are the building blocks of proteins (a subject which I want to blog about another time) which are essential to life.  There are left-handed and right-handed versions of them, designated L and D respecitively.   In chemistry, there is in general no preference between the two, and most reactions will result in equal numbers of each (called racemic).  However, in nature generally only L-amino acids are found in proteins.  Why this “homochirality” occurs is under much debate, but the above (and simlar) research may point in some promising directions.

ChemistryChiral molecules are those for which the atomic pattern differs from its mirror image.  The differences can be described by the following:

1. Configuration (R/S) – The relative position of the atoms in a molecule as it relates to their atomic numbers.
2. Configuration (D/L) – The relative position of the atoms as it relates to the molecule glyceraldehyde.
3. Optical Activity (+/-) – How a solution of the molecule rotates polarized light.

PhysicsAccording to wikipedia: “The chirality of a particle is more abstract. It is determined by whether the particle transforms in a right or left-handed representation of the Poincaré group.”  Unfortunately I do not understand the slightest about this group (a 10-dimensional lie group which represents the isometries of Minkowski spacetime), so it will have to wait for its own blog posting after some research.  Anyway, what is so interesting about chirality in physics, and what our insightful commenter alluded to, is that the weak interaction (one of the 4 fundamental forces of nature) only acts on left-handed fermions!  Remember that fermions have half-integer spin and make-up all matter due to their adherence to the Paui Exclusion Principle,  Nature is sometimes not as symmetrical as we would like her to be.

Mathematics Again from wikipedia: “A figure is achiral if and only if its symmetry group contains at least one orientation-reversing isometry. (In Euclidean geometry any isometry can be written as $v\mapsto Av+b$ with an orthogonal matrix A and a vector b. The determinant of A is either 1 or -1 then. If it is -1 the isometry is orientation-reversing, otherwise it is orientation-preserving.)”