The order from smallest to largest would be:
H < C < N < O < Amino acid sequence < Globular Structure < Amino acid
The smallest should start from the elements. Among C, H, O and N, the lightest is the hydrogen, followed by carbon, nitrogen, then oxygen. You'll know this based on the periodic table. Next, is the amino acid sequence. This is the linear structure. Following is the globular structure which is the tertiary structure. The whole would be the amino acid.
