Man vs Nature Man prefers the Right while Nature apparently favours the Left
Professor Dhaneshwar Moirangthem
We, human beings, are blessed with two hands- the left hand and the right hand. In terms of activities and performing physical works, both hands are not used equally. Majority of people prefer to use the right hand while a small but significant minority use the left hand. Those who use their right hands predominantly are dubbed the right-handed persons and the rest left-handed persons.
By traditions and by religious beliefs, we used to discriminate against the left hand vis-à-vis the right hand. From our childhood, we are somehow made to believe that the right hand is more sacred than the left hand. While offering flowers to gods and goddesses, while giving something to or receiving something from someone, we are taught to use the right hand as if the left hand is somewhat impure.
If you use your left hand to give something to a guest, people may think you are insulting the guest. We use our right hand for eating, for picking up good things and for doing other niceties while our left hand is left to do other dirty jobs like picking up distasteful things, washing one’s bottom, etc. What a discrimination it is, even though both hands belong to the same person. Even left-handed persons use the right hand while shaking hands with friends and colleagues. The superiority of the right hand over the left hand is almost complete.
If new-born children are left alone (so far as the use of the hands are concerned) there is a possibility that fifty percent may turn out to be left-handed and the other fifty percent right-handed when they grow up. There is also the possibility that the person, when they are grown up, may use both hands equally; he/she may not be a right-handed or a left-handed person. But ultimately, of course, he/she may use one of them in preference to the other as time goes on, because on many occasions only one of them will be used.
In the Western and European countries, where the traditional beliefs and religious mindsets are different from those of us in the East, there is less discrimination between the left and right hands. But still, left-handed people did not always have it easy in that part of the world. In the past, they were assumed to be weak and wicked, labelled as evil, considered to be witches, involved in witchcraft. The word ‘Sinister’ comes from Latin word, meaning ‘Left’, as in the left-handed. Even the Devil himself was considered a southpaw, and he and other evil spirits were also believed to be conjured up by the left-handed gestures. In many parts of the world, two-thirds of the world’s population still view being left-handed as defects. In certain parts of Africa, Europe, and the Far-East, it is actually offensive to do anything with your left hand.
Not only is the preference of right over the left-hands, but we also used to give higher priority to the right over left in placements or positions. While making seating arrangements in a formal function, the Chairman/President is usually seated on the right of the Chief Guest. In religious or societal functions, we usually arrange to see that the elder is seated on the right rather than the left. The matter does not end here. We just look at the monthly calendar hanging on the wall, the dates of the week are arranged from left to right in increasing numbers. The preference of right over left (in order of hierarchy) is also vividly visible in Roman Numerals, where the Romans used Roman/Latin alphabets for numbering. For instance, the letter ‘X’ represents ten in Roman Numerals; if we put ‘I’ (one) on the right it becomes XI (eleven) and ‘I’ on the left hand, it becomes ‘IX’ (nine). Likewise, the letter ‘L’ represents fifty, ‘XL’ and ‘LX’ become forty and sixty, respectively. In physical, chemical, and biological sciences, the most important and significant table of elements is the Mendeleev’s Periodic Table. In the Periodic Table, the elements are arranged in a period from left to right in order of increasing atomic number, the elements of lowest atomic number on the left and highest atomic number on the right in a period.
Is Nature Left-Handed?
Having discussed the human preferences, let us have a look at how nature is dealing with biomolecules which are essential components of living beings. These biomolecules are synthesized in nature by various biochemical processes. The most important biomolecules are Proteins, Nucleic Acids, Fats, Carbohydrates, Vitamins among many others. For the purpose of the present discussion, let us confine our attention to proteins. The name Protein is taken from the Greek word ‘Proteios’, which means first rank (number one). Of all chemical compounds (biological compounds as well), proteins must almost certainly be ranked number one for they are the substance of life. Proteins make up a large part of the animal body, they hold it together, they run it. They are found in all living cells, they are the principal material of skin, muscle, tendons, nerves, and blood. They are also the principal components of enzymes, antibodies, and many hormones. Only the Nucleic Acids (DNA, RNA, etc) which control heredity, can compete with proteins in terms of ranking and they are important because they direct the synthesis of proteins.
Actually, all biomolecules are important for the sustenance of the living being. Chemically, proteins are high polymers. They are polyamides, and the monomers from which they are derived are a-amino-carboxylic acids. A single protein molecule contains hundreds or even thousands of amino acid units. These units can be of twenty-odd different kinds. The number of different combinations, that is, the number of different protein molecules that are possible is almost infinite. It is likely that tens of thousands of different proteins are required to make up and run an animal body.
The a-amino acids are the constituent unit of proteins, a polymer linked together by Peptide Bonds. The peptide bond is obtained by the reaction of the amino group of one amino acid with the carboxylic group of another amino acid. The amino acids may be the same or different. The a-amino acids, as the name suggests has the amino group (-NH2) attached to the a-carbon (carbon atom next to the carboxylic group, -COOH) of the molecule. The a-carbon atom (except in glycine, H2NCH2COOH) is found to be asymmetric. When the four valencies of carbon (tetravalent carbon) are satisfied by four different ligands, the carbon is said to be asymmetric.
During our undergraduate days in the latter half of 1960’s, the then chemistry teacher used to compare tetravalent (four handed) carbon with the four handed Hindu God, Lord Vishnu, who is omnipresent, most powerful and can evolve to several incarnations (avatars). In the chemical/biological world, carbon is the most important and omnipresent element. I now realize that the comparison of the element carbon (C) with the Supreme Godhead Vishnu, is quite appropriate. Of all the various elements that are available today, the element carbon must occupy the top rank. From coal to graphite to diamond; from petrochemicals to proteins, nucleic acids, carbohydrates; from alkaloids to life saving drugs; from our food to dressing and building materials, carbon is indispensable. Just like Lord Vishnu carries four items (weapons) in his four arms; Shankha, Chakra, Gada and Padma, when carbon carries four different ligands, it exhibits unique properties- the optical activity and stereogenicity. Optical activity of a molecule is the ability to rotate the plane polarized light to the right (+), clockwise (dextrorotatory) or to the left (-) anticlockwise (laevorotatory). The stereogenicity is the property associated with the carbon- the ability to generate a new isomer (avatar or an incarnation) when two of its ligands exchange their positions. For instance, when the amino (-NH2) group is on the left side of a-carbon in the amino acid in the Fischer Projection, it is called L-isomer; when it is on the right, it is called the D-isomer; they are different compounds. The ‘D’ and ‘L’ are derived from the Latin words dexter (right) and Laevus (Left).
Of the twenty-three a-amino acids obtained in nature, all the a-carbon atoms are asymmetric except the a-carbon in glycine, because it carries two hydrogen atoms; that means all the ligands are not different in this particular compound. When one tries to synthesize an asymmetric a-amino acid using ordinary synthetic procedure, there is equal possibility that the amino group may be on the left or on the right of the a-carbon, which means the result will be a mixture of equal proportion of D- and L isomers. This process is called racemization. If special care is taken, using asymmetric reagents as catalysts, one may get a product which is predominantly D-isomer or L-isomer (not both). This process is called Asymmetric synthesis.
The a-amino acids present in proteins are obtained by asymmetric synthesis in nature which is probably catalyzed by enzymes which are themselves proteins and are asymmetric and optically active. The enzymes are known for their extreme specificity in their actions; they will catalyze the formation of only one type (D- or L-) and not both; they may catalyze one reaction, but they will not catalyze another similar reaction. What is surprising is the fact that all the twenty-two asymmetric amino acids found in proteins have the L-configuration-that is they are all L-Amino acids. It is mysterious that no D-Amino acids are obtained in nature. It is a phenomenon hard to explain.
One possibility (it is simply an assumption, and not based on established facts) is that when life began millions of years ago, the first amino acid molecule formed could be, by chance, the L-amino acid. When subsequent amino acids are formed, the process is influenced by the already existing L-amino acid and as a result only the L-isomers are formed. If the reactions were catalyzed by enzymes, as they are very specific, they could have catalyzed only the formation of the L-isomers. That is probably how we end up with only the L-amino acids in nature. Another possibility is that the L-amino acids are more stable than their opposite counterparts (D-isomers) in their asymmetric environment in nature. Another reason could be that the D-isomers are not useful to the living beings and hence rejected in nature.
To be contd