What are the four levels of protein structure? Please name and describe each level.

Primary - where amino acids are in the correct order in the polypeptide chain.

Secondary - where small structures within the chain begin to form (including alpha helices and beta pleated sheets).

Tertiary - where more complex structures form due to more bonds forming. This is the final, three-dimensional structure of a protein with only one chain.

Quaternary - when the final protein consists of more than one polypeptide chain.