The levels of protein structures are: PRIMARY, SECONDARY AND TERTIARY STRUCTURES.
The amino acid sequence and the bonding types between the amino acids determine the structures of proteins. Protein structures also determines the function of a protein, if a protein losses its structure it will not be able to perform its function again.
Functional groups play an important role in the formation of protein structure.Functional groups also participates in specific biochemical reactions in the body thus enabling the proteins to perform their functions.