Final answer:
Proline is generally absent from alpha-helices due to its ring structure introducing rigidity, causing a kink in the helix. Serine, threonine, and tyrosine can be phosphorylated because they contain hydroxyl groups. Hydrophobic amino acids like Trp tend to be located within the protein's interior.
Step-by-step explanation:
The amino acid generally absent from an alpha-helix is proline (Pro). Proline acts as a helix breaker because its side chain bonds back to the amino group in the peptide backbone forming a ring structure. This unique structure introduces rigidity and causes a kink in the helix, disrupting the regular hydrogen bonding pattern critical for the stability of the alpha-helix.
The property that enables the amino acid residues serine, threonine, and tyrosine to be phosphorylated is that they contain a hydroxyl group. This group can react with phosphate groups to form phosphoester bonds, which are commonly involved in the regulation of protein function and signaling pathways.
Hydrophobic amino acids, such as Trp, are usually found within the interior of proteins to promote proper folding and stability by avoiding water.