蛋白质折叠

After the formation of its secondary structure, a protein collapses into a tertiary globular form, a unique and individual 3D confirmation that guides its function.

More specifically, the folding patterns are determined by different chemical interactions. First, the compactness is governed by hydrophobicity of the amino acid side groups, such that non-polar chains are pushed inside creating a hydrophobic core away from the aqueous environment. Weak van der Waals attractions help maintain the clustered core.

On the outside mostly lie the amino acids with charged or polar side chains, free to interact with water. Side chains with opposite charges can form ionic bonds, while similarly charged sides repel each other. Polar side chains can form hydrogen bonds, either with water or other polar molecules.

Lastly, acting as reinforcement are disulfide bridges. These bonds occur between two adjacent cysteine monomers, which contain sulfhydryl or SH groups on their side chains. The sulfur on one bonds covalently to the second. The presence of these chemical interactions and bonds secure the protein in its most favored confirmation.