Hydrophobic sidechains Hydrophobic Amino Acid- will be buried on the inside of the globular protein, where they are hidden from polar water molecules. Charged sidechains (+) and (-) will be on the surface of proteins where they often neutralize each other and form salt bridges. Polar sidechains Polar Amino Acid- will be on the surface of the protein where they can hydrogen bond with water. Cysteine sidechains Cysteine amino acid-often interact with each other to form covalent disulfide bonds that stabilize protein structure. Basic Laws of Chemistry that Drive Protein Folding Stably folded proteins simultaneously satisfy several basic laws of chemistry including:

A. What is a disulfide bond? A single covalent bond between the sulfur atoms in two amino acids called cysteine. B. What is the significance of disulfide bonds? They are very important in determining the tertiary structure of proteins They are very important in determining the quaternary structure of some proteins. A very prominent example would be the role of disulfide bonds in the structure of antibody molecules.

What is a salt bridge? Salt bridges fall into the broader category of non-covalent interactions. A salt bridge is actually a combination of two non-covalent interactions: hydrogen bonding and electrostatic interactions.

Wild type (left) and mutated (right) form of lamin A. Normally, arginine (blue) forms salt bridge with glutamate (magenta), but a mutation results in breaking this interaction (leucine is too short to reach glutamate) and structure destabilization. At phenotype level this manifests with progeria syndrome and other genetic mutations.