1) All Lamino acids have an S absolute configuration except L-cysteine, which has the R configuration. Explain what is unique about L-cysteine that would cause it to be designated as having an R absolute configuration despite sharing a similar three-dimensional structure with the other L amino acids.
Cysteine contains a Sulfhydryl group in its side chain that is attached to the asymmetric carbon or chiral carbon.
R and S configurations are assigned according to the priority of groups attached to the asymmetric Centre.
All L-amino acids have an S absolute configuration as the priority groups attached to asymmetric carbon from highest to lowest are in counter clock wise direction when looked form the least priority group.
but when it comes to cysteine the Sulphur attached to the carbon in the side chain is having more priority compared to COOH group.
hence in cysteine the priority order is NH2CH2SHCOOH H
So the absolute configuration of L-Cysteine becomes R as the priority groups attached to asymmetric Centre are in clock wise direction where as in other amino acids it is not the same.
Step by step
Solved in 2 steps with 1 images
