Post by general313 on Feb 12, 2019 20:17:32 GMT
You may have noticed that there is a lot of arbitrariness in a language. Somebody invents a new word, say "boy". In another language they might come up with "ragazzo". Once these arbitrary words are thought up they get passed on from generation to generation, so after many generations the Italians keep using "ragazzo" and the English "boy". It is erroneous to say that each generation having the same word is like tossing a coin and always getting heads.
Sugars are much the same way. A sugar evolved that goes one way (right or left), which has a specific DNA representation different from the other way, and once developed the gene gets passed from generation to generation, like a word in a language. Also erroneous to compare to repeated coin tosses.
Sugars and amino acids are capable of being put together either way, but once assembled they are stable in one configuration or the other, and do not change from one to the other. The assembly of these molecules is directed by DNA, RNA, and enzymes (themselves made up of amino acids) in the nucleus of a cell, in such a way that the handedness is explicitly laid out in the gene. Once the gene for the sugar or amino acid has evolved it gets passed on to future generations. Evolution explains the handedness quite nicely if you take the trouble to understand the science.