Answer :
The primary structure occurs when the protein structure is only a chain of amino acids, with no folds or twists. Therefore, b) is incorrect.
This primary structure then twists folds in itself, creating the structure that's folded and held in shape by hydrogen bonds. That's the secondary structure, and whats is folded in it is the amino acids. Therefore, c) is the correct answer.
The tertiary structure is a three-dimensional structure, shaped by interactions between the R groups of the amino a cids. To form this structure, the entire secondary structure elements (not the amino acids) are folded together. Therefore, a) is also incorrect.
The quaternary structure is a closely pack arrangement of several protein chains, each with its own primary, secondary and tertiary structure. Therefore, d) is wrong as well.
