issue of Science journal of july
2005 reported 100 questions that span
the sciences (Sciences,
2005, vol. 309 - page 86). It
is expected that some will drive scientific inquire for a long time
soon be answered.
A very intriguing question was: "What is the origin of homochirality in Nature?"
|The origin of the preference between mirror-images of natural molecules (such as amino acids and sugars) still remains a mistery.|
acids are individual building blocks that comprise proteins. About 500
amino acids are known and have been classified in many ways (Wagner and
Musso - 1983).
The classification is done on the basis of:
are D-amino acids?
Amino acids exists in two orientation in the space: levorotatory (L) and dextrorotatory (D), also indicated as left-handed and right-handed. The majority of amino acids (D-AA) in living organisms are L-isomers. In the last few decades with the advancement of technology, the presence of D-amino acids was discovered in living things. This finding opened the questions related to their origin, synthesis, and physiological roles.
select the L-enantiomer?
D-amino acids do not bind tRNA molecules, thus their presence in proteins is related to posttranslational modifications (Doolittle, 1983).
Recently, it was demonstrated that the cellular translational machinery accepts D-AA-tRNAs into the ribosomial AA tRNA binding site A, uses it as a peptidyl - transfer acceptor, and traslocates the resultating peptidyl-D-AA-tRNA into the ribosomial P (peptidyl) site. Subsequently, the latter traps the ribosomal peptidyl-transferase center in a conformation that impairs peptidyl transfer, (Englander et al., 2015).