Final answer:
The amino acid that has both a chiral alpha carbon and a second chiral carbon in its side chain is Isoleucine.
Step-by-step explanation:
The question asks which amino acid has not only a chiral alpha carbon but also a second chiral carbon in its side chain (R group). A chiral carbon is a carbon atom that is attached to four different groups, and the presence of this type of carbon allows for the existence of enantiomers which are non-superimposable mirror images of each other. When looking at the list of amino acids provided, we note that all proteinogenic amino acids (those that are incorporated into proteins) have a chiral alpha carbon except for glycine.
The amino acid that fits the criteria of having an additional chiral carbon in the side chain is Isoleucine. Isoleucine not only has a chiral alpha carbon but also has a second chiral carbon within its aliphatic side chain. This is in contrast to Serine, Threonine, and Alanine, where only threonine has another chiral center besides the alpha carbon.