Large proteins consist of more than one polypeptide chain and possibly a non-peptide prosthetic group.The polypeptide chains are held together by ionic, covalent (disulfide bridges) and hydrogen bonds.Hydrophobic interactions are attractive forces between non-polar groups in aqueous environments.Hydrophilic interactions are attractive forces between polar groups in aqueous environments and water molecules.Both hydrophobic and hydrophilic interactions affect the tertiary and quaternary structure of proteins.