Chirality of Nucleotides?

Michael Dorsett Onken mdonken at
Fri Oct 31 16:35:09 EST 1997

Christopher Bruce Peart (cpeart at wrote:
: I have a  few questions that I have not been able to find a satisfying
: answer to.  In a textbook of mine, in a section of DNA,  AMP is drawn with
: the phosphate group on the 5' carbon of ribose and the adenine on the 3'
: carbon.  On another page, showing ATP hydrolysis, each group is on the
: opposite carbon (mirror image minus two phosphates).  Which one is
: correct?  Are both enantiomers of ATP used in energy production?  Does one
: enantiomeric form of the nucleotides cause a 'right-handed' (clockwise)
: helix and the other a 'left-handed' (counter-clockwise) helix?  

In all nucleotides, the base (purine, pyrimidine, etc.) occupies the 1'
position of ribose.  In AMP, ADP, and ATP, the phosphate moiety is
bound to the 5' carbon.  In DNA (which lacks the 2' hydroxyl) the 
phosphate ester backbone bridges 5' to 3'.  Likewise for linear RNA
molecules, however branchpoints (5' to 2') as in intron lariats can also
occur in RNA.  L-ribose is not recognized by any of the nucleic acid
synthesis machinery, and is not part of DNA, RNA, or nucleotides.  Z-DNA
(left-handed helix) does exist, but using D-ribose.

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