All amino acids except [a] have an chiral carbon. All amino acids except [b] have a beta carbon.

To answer your question, we can identify amino acids that have unique characteristics regarding chiral carbon and beta carbon presence.

1. Identify Amino Acids:

   • Chiral Carbon: A chiral carbon atom is one that has four different substituents attached to it. Most amino acids possess this property, except for glycine. Glycine is the only amino acid without a chiral center because its side chain is a hydrogen atom, which results in it having two of the same substituent.
   • Beta Carbon: The beta carbon is the second carbon atom in the amino acid chain, which typically follows the alpha carbon (attached to the amino group). Amino acids like glycine and proline do not have a beta carbon in a traditional sense as they are structurally distinct. However, proline does have a cyclic structure that modifies its usual amino acid configuration.

2. Conclusions:

   • For the chiral carbon, the answer is [a] glycine.
   • For the beta carbon, the answer is more nuanced, but a straightforward conclusion can be drawn by understanding proline's structure in a specific context. Thus, the best answer here is [b] proline if we consider the unique constraints of beta-carbons in certain cyclic structures.

In summary:

• [a] Glycine (no chiral carbon)
• [b] Proline (considered to have a unique arrangement that may suggest the absence of a typical beta carbon)