Describe how proteins fold, mentioning at least three rules followed by the amino acids.

Protein folding is determined by a variety of factors, from the amino acid composition all the way through to primary, secondary and tertiary structures of the proteins. Proteins fold in water environments, and how they fold is determined by the hydrophobicity, hydrophilicity and charge of amino acids. Amino acids that are hydrophobic will face away from water environments, while hydrophilic amino acids will face towards water environments. This gives rise to primary and secondary structures such as alpha-helices and beta-sheets. Among these are a variety of structures that form the tertiary structures. The different types of amino acids play an essential role in this, as they are the building blocks of proteins and can affect the structures of proteins because of their charge and affinity for water.