Only free-form amino acids are transported through the blood. Normal proteins from wheat, milk and di- or tripeptides must be broken down into free-form amino acids in the digestive tract before they can be absorbed. A peptide is a molecule that is created when two or more amino acids are joined together. Other forms, such as pyroglutamate, monohydrate, fumarate or tartrate are preferential for certain amino acids. The free-form amino acids pyroglutamate, monohydrate, fumarate or tartrate are more expensive to produce than simple milk-, egg- or wheat proteins. Amino acids affect: mood, alertness, energy, concentration, vitality, immune system, aggression, sleep, muscle building, enzyme function and the composition of DNA.