primary, secondary, tertiary, & quaternary structures

primary structure

• amino acid sequence

• even a slight change in this can alter tertiary structure

• level of structure that is held together by peptide bonds

secondary structure

• alpha helix and pleated sheet

• coiling & golding produced by hydrogen bonds between —NH and C=O groups

tertiary structure

• overall 3D shape

• stabilized by clustering of hydrophobic R groups, hydrogen bonds, and ionic bonds

• "globular" or "fibrous" might describe this level of structure

quaternary structure

• this level occurs in proteins with more than one polypeptide subunit

• not present in all proteins