AAPPTec - Complete Peptide Product Source

A peptide consists of two or more amino acids linked together by amide bonds.

Proteins consist of approximately 100 or more amino acids linked together by amide bonds.  Proteins generally have complex 3-dimensional structures and may have several subunits.  Enzymes, receptors and the structures that produce motion are typically proteins.

The basic difference between peptides and proteins is size.  Compounds containing 50 amino acids or less are generally called peptides while compounds consisting of more than 100 amino acids are usually called proteins.  Between 50 and 100 amino acids, however, there is little agreement as to where the demarcation between peptides and proteins exists. 

Probably the most practical deliniation is if a product could be efficiently prepared by solid phase synthesis techniques, it is a peptide while products too large to be efficiently prepared are proteins.