Final answer:
Functional proteins favor intrachain H-bonding for stability, supported by ionic bonds, hydrogen bonds, and disulfide linkages, contributing to their functional tertiary structure.
Step-by-step explanation:
Functional proteins generally favor intrachain hydrogen (H) bonding. Intrachain H-bonding involves the formation of hydrogen bonds within the protein chain itself, which contributes to the stability of the protein's tertiary structure. Various attractive forces stabilize this structure, including hydrophobic interactions, ionic bonding, hydrogen bonding, and disulfide linkages, as indicated in Figure 7.21 and further elaborated on in Figures 16.5.5, 18.8.5, 19.5.5, and 19.6.5. Ionic bonds occur between charged side chains, hydrogen bonds form between polar amino acids, and disulfide linkages form between cysteine residues, all leading to the tertiary structure that is essential for the protein's function.