The amino acid tryptophan can act as a precursor for which of the following neurotransmitters?

The amino acid tryptophan can act as a precursor for which of the following neurotransmitters? A) Dopamine B) Serotonin C) Acetylcholine D) GABA In the structure of proteins, which amino acid interrupts α-helix formation due to its rigid cyclic structure? A) Proline B) Glycine C) Alanine D) Leucine