How many chiral carbons do most amino acids found in proteins contain? Which ones contain

an additional chiral carbon? How do the chemical properties of an L$-$ and its corresponding D$-$

amino acid differ? How do their biological properties differ? Explain. Answer the same question

for L$-$threonine and L$-$allo$-$threonine, which differ only by the configuration around the side

chain chiral carbon