Final answer:
Ionic interactions do occur in native proteins and are essential for stabilizing their tertiary structure. These interactions are facilitated by charged amino acid residues that contribute to protein structure. Proteins in their native state utilize ionic bonding, hydrogen bonding, hydrophobic interactions, and disulfide linkages for proper folding. Option D is correct.
Step-by-step explanation:
The question as to why ionic interactions are not seen in native proteins is multifaceted. Ionic bonding is, in fact, a significant force in determining the tertiary structure of proteins. When proteins fold into their native structures, ionic bonding, along with hydrogen bonding, hydrophobic interactions, and disulfide linkages, are essential in stabilizing the structure.
The statement that proteins lack charged residues is incorrect because amino acids do have side chains that can be positively or negatively charged, enabling ionic interactions. In the native state of proteins, ionic interactions are not energetically unfavorable; rather, they contribute to the stability of proteins by facilitating attractions between amino acids with opposite charges.
Additionally, ionic interactions do not disrupt folding; on the contrary, they are part of the complex network of interactions that promote proper folding. Proteins also do not maintain an overall neutral charge; they can have a net charge at any given pH depending on the ionization state of their amino acid side chains.