Rajasthan BoardEnglish MediumSTD 12 ScienceChemistryBiomolecules2 Marks
Question
Describe the term $D\ -$ and $L\ -$ configuration used for amino acids with examples.
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Answer
The sugars are divided into two families: the $D\ -$ family and $L\ -$ family which have definite configurations.
These configurations are represented with respect to glyceraldehyde as the standard.
The glyceraldehydes may be presented by two forms as:
$D\ -(+)-$ Glyceraldehyde $L\ -(-)-$ Glyceraldehyde The $D\ -$configuration has $-\ce{OH}$ attached to the carbon adjacent to $-\ce{CH_2OH}$ on right while $L\ -$ configuration has $-\ce{OH}$ attached to the carbon adjacent to $-\ce{CH_2OH}$ on left.
The sugars are called $D\ -$ or $L\ -$ depending upon whether the configuration of the molecule is related to $D\ -$ glyceraldehyde or $L\ -$ glyceraldehyde.
It has been found that all naturally occurring sugars belong to $D\ -$ series,
e.g., $D\ -$ glucose $D\ -$ ribose and $D-$ fructose.
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