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16

The ribosome holds the peptide-bound tRNA and aminoacyl-tRNA in the right orientation to catalyze the peptidyltransferase reaction. http://www.pnas.org/content/103/36/13327/F1.expansion.html If the incoming aminoacyl-tRNA was the other enantiomer, the amino acid moiety would not fit properly into the ribosome active site. In other words, the shape of the ...


15

I know that you are referring to the commonly ribosome-translated L-proteins, but I can't help but add that there are some peptides, called nonribosomal peptides, which are not dependent on the mRNA and can incorporate D-amino acids. They have very important pharmaceutical properties. I recommend this (1) review article if you are interested in the subject. ...


9

For the most part they are not used. there are amino acid racemases, which interconvert L- and D- forms of some specific amino acids, which may be used in some particular biosynthetic or metabolic pathways. In particular I'm thinking of firefly luciferase which uses D-Cysteine as a re-dox reagent to regenerate the luciferin substrate that the light - ...


7

As far as I know, it is unknown why we only see left-handed and not right–handed amino acids. A recent article speculates that the weak force could be responsible for a tiny asymmetry in energy levels between the stereo-isomers. However, if the effect is tiny, its hard to see why it should have biological implications. In 2004, Tamura and Schimmel showed ...


6

The normal results of an attempt to assemble proteins with mixed chiral amino acids is a protein that fails to fold. The general assumption due to this result is a choice has to be made very early on to use all right-handed or all left-handed amino acids. There doesn't seem to be any particular reason to choose one way over the other except for prevalence.


5

You may also be interested in D-amino-acid oxidase (EC 1.4.3.3), a flavoprotein (FAD) highly specific for the D-form of amino acids, which was discovered by Hans Krebs in 1935 (see here), and which has a wide distribution (including in humans). The enzyme has been very thoroughly investigated, in particular by Massey & co-workers (see here for ...


1

Microscopic chirality is not at all necessary to explain curly hair (or other objects). All that is required is flexibility. Once hair gets long enough, it collides with itself, and is pushed off to one side or another, forming a chiral curl. For some anecdotal evidence against microscopic chirality, find someone with large diameter hanging curls in their ...



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