Molecules Recognise Each Other!

How Individual Molecules Recognise Each Other?

If one thinks that there are thousands of times more molecules forming our body than stars in the universe it is astonishing how all these molecules can work together in such an organised and efficient way. How can our muscles contract to make us walk? How can food be metabolised every day? How can we use specific drugs to relieve pain?




To work as a perfect machine, our body ultimately relies on the capability of each little part (molecule) to know a specific function and location out of countless possibilities. To do this, molecules carry information in different ways. The key to understanding all biological processes is recognition. Each molecule has a unique composition and shape that allows it to interact with other molecules. 
A number of molecules can recognise each other and transfer information exactly in a way, they can either be "right handed" (D) or "left handed" (L). This property called "chirality" is a spectacular way to store information: a chiral molecule can recognise molecules that have the same chirality (same "handedness", L to L or D to D) and discriminate the ones of different chirality (L to D and D to L). 

Probably one of the most exciting mysteries of Nature is why the building blocks of life, i.e. amino acids (the building blocks of proteins) are exclusively present in the chiral L form and sugars (which constitute DNA) are all in the D form. Once more, the reason for this preference is "historical", but this time goes back millions of years till the origins of the biological world. Researchers think that current life forms could not exist without the uniform chirality ("homochirality") of these blocks, because biological processes need the efficiency in recognition achieved with homochiral substances. In other words, the separation of molecules by chirality was the crucial process during the Archean Era when life first emerged.

It has been seen that two molecule, let say (diphenylalanine, the core recognition motif of Alzheimer amyloid polypeptide) of the same chirality can form structures (pairs, chains) while molecules of different chirality discriminate and cannot form stable structures.
As it occurs when you shake the hand of your friend, the fact that the two homochiral hands are complementary by shape is not enough, you both have to dynamically adapt and adjust your hands to reach a better fit, a comfortable situation. This dynamic mechanism of how two molecules "shake hands" and recognise each other by mutually induced conformational changes at the single molecule level. 
We live in houses, wear clothes and read books made of chiral cellulose. Most of the molecules that mediate the processes of life like hormones, antibodies and receptors are chiral. Fifty of the top hundred best-selling drugs worldwide are chiral... there is lot more to know, to understand , to emphasis the big and key term that is "LIFE" ....