The natural proteinogenic amino acid alanine is represented by the following Fischer projection (R=CH₃), and therefore is L-alanine.

What is the configuration (R or S) of

• L-alanine,

• the natural proteinogenic amino acid L-serine,

• the natural proteinogenic amino acid L-cysteine,

all of which are represented by the above Fischer projection, having R = CH₂OH (serine), and R = CH₂SH (cysteine)?

L-alanine R S

L-serine R S

L-cysteine R S