Polypeptide chains are composed of 20 different types of amino acids, each with specific variable side chain

• These side chains will have distinct chemical properties (e.g. charged, non-polar, etc.) and hence cause the protein to fold differently according to its specific position within the polypeptide chain
  

• The way a protein molecule folds plays a critical role in determining its eventual function and level of biological activity
  

As most natural polypeptide chains contain between 50 – 2000 amino acid residues, organisms are capable of producing a huge range of possible polypeptides

• Consequently, proteins are a very diverse class of compounds and may serve a number of different roles within a cell
  

Functions of Proteins

Proteins perform an array of functions:

• Structure (collagen, spider silk)

• Hormones (insulin, glucagon)

• Immunity (antibodies)

• Transport (protein channels)

• Sensations (rhodopsin)

• Movement (actin, myosin)

• Enzymes (Rubisco, amylase)