Which of the following is the least likely to be involved in stabilising the three-dimensional folding of most proteins?
(a) Hydrogen bonds
(b) Electrostatic interaction
(c) Hydrophobic interaction
(d) Ester bonds
(d) Ester bonds are the least likely to be involved in stabilising the 3D-folding of most proteins. A long protein chain gets folded upon itself like a hollow woolen ball, giving rise to a tertiary structure (3D) structure. This structure is stabilised by several type of bonds, i.e. hydrogen bonds, ionic bonds, Vander waal's interactions, covalent bonds and hydrophobic bonds. Ester bond is formed between sugar and phosphate in a nucleotide and is not involved in stability of a polypeptide chain. Thus, option (d) is correct.