What Is a Peptide Bond? Understanding the Formation of Amino Acid Chain in the Human Body

Protein is an important component of a healthy body as it helps repair and build tissues. The building blocks of proteins are called amino acids, characterized by small organic molecules made of a central carbon atom connected to an amino group, a carboxyl group, a hydrogen atom, and a side chain. In forming a protein, multiple amino acids are linked together by peptide bonds to form a long chain.

What is a Peptide?

The word peptide comes from the Greek word "digested" and refers to a short chain of two or more amino acids. When organized in complex structures of 50 or more amino acids, peptides can become proteins. Peptides perform various bodily functions and serve as the basis of several medications.

Peptides are mainly classified into three different groups. They can be categorized according to their functions in the human body and according to their source, whether plant or animal. Another way to classify peptides is by the number of amino acids that comprise the chain.

Different types of peptides play a significant role in the human body. For instance, vasopressin, a peptide hormone secreted in the hypothalamus, is responsible for regulating the amount of water in the extracellular fluid. Another peptide hormone called oxytocin causes the uterus to contract during childbirth. Some defensins promote wound healing, and angiotensins aid in regulating blood pressure.

Peptides are found to possess antimicrobial, antioxidant, and anti-clotting effects. As of 2017, there are over 60 therapeutic peptides that have been approved in the U.S. and other countries around the world.

What is a Peptide Bond?

A peptide bond is a chemical bond formed by joining the carboxyl group of one amino acid to the amino acid of another. Also known as an eupeptide bond, a peptide bond is an amide-type of the covalent chemical bond.

The formation of peptide bonds involves the release of water molecules. Since the water molecule is eliminated, this type of bond is considered a dehydration process that occurs mostly between amino groups. At the molecular level, a peptide bond is formed by a dehydration synthesis known as a condensation reaction.

Peptide bonds are strong and are characterized by partial double bonds. This means they are not broken by high temperature or salt concentration. They can only be broken by exposure to strong acids or bases for a long time at high temperatures and specific enzymes.

Another characteristic of peptide bonds is the presence of rigid and planar bonds, which stabilize the protein structure. They also contain partial positive charge groups and partial negative charge groups in their structure.

Due to resonance stabilization, a peptide bond is usually unreactive under physiological conditions. In some cases, however, peptide bonds can undergo chemical reactions mostly due to an attacking electronegative atom on the carbonyl atom. As a result, the carbonyl double bond and the formation of a tetrahedral intermediate is broken.