Biochemistry, Peptide

Excerpt

Peptides play an essential role in fundamental physiological processes and are necessary for many biochemical processes. A peptide is a short string of 2 to 50 amino acids, formed by a condensation reaction, joining together through a covalent bond. Sequential covalent bonds with additional amino acids yield a peptide chain and the building block of proteins.

Peptides are named based on the number of amino acid residues in the sequence. As peptide chains form between joining of the primary structure of amino acids, they may enlarge to become an oligopeptide when there are between 10 to 20 amino acids in the chain. In vivo, each amino acid is added to the amino-terminal of one amino acid to form a peptide chain. When there are greater than 20 amino acids, the peptide is an unbranched chain deemed a polypeptide.

Each amino acid comprising a peptide is called a “residue” since that is the portion remaining after the loss of water in the dehydration reaction. Amino acids are the organic starting molecule composed of a carboxyl-terminal and an amino group that makes up the foundation of a protein. Peptide synthesis depends on three main reactions: 1. an amino acid goes through a deprotection step, a preparatory reaction that adds the next amino acid to the chain, and lastly, a coupling reaction that forms the final peptide with functionality. In the second step, the amino acid becomes activated with several reagents. Thes carboxylic acid in the amino acid will react to make the activated form, which will then enter into a coupling reaction. After one round of peptide synthesis, this process is repeatable to add more amino acids until creating the desired length of the peptide.

Peptide bonds are resistant to conditions that denature proteins, such as elevated temperatures and high concentration of urea. Amino acids all have the same general structure, with a positive charge on nitrogen and negative on the carbonyl group.