Peptide Bonds | Peptide Information

Notice

ALL ARTICLES AND PRODUCT INFORMATION PROVIDED ON THIS WEBSITE ARE FOR INFORMATIONAL AND EDUCATIONAL PURPOSES ONLY. The products offered on this website are furnished for in-vitro studies only. In-vitro studies (Latin: in glass) are performed outside of the body. These products are not medicines or drugs and have not been approved by the FDA to prevent, treat or cure any medical condition, ailment or disease. Bodily introduction of any kind into humans or animals is strictly forbidden by law.

What is a Peptide Bond?

A peptide bond is a covalent bond that is formed between two amino acids. To form a peptide bond, a carboxyl group of one amino acid reacts with the amino group of another amino acid. As a result, a molecule of water is also released. This is referred to as a condensation reaction. The resulting bond is a CO-NH bond and is henceforth referred to as a peptide bond. Additionally, the resulting molecule is termed an amide.

Peptide Bond Formation

In order to form a peptide bond, the molecules of the amino acids in question must be orientated so that the carboxylic acid group of one amino acid is able to react with the amine group of another amino acid. At its most basic, this can be illustrated by two lone amino acids combining through the formation of a peptide bond to form a dipeptide, the smallest peptide (i.e. only composed of 2 amino acids).

Any number of amino acids can be joined together in chains to form new peptides: as a general guideline, 50 or less amino acids are referred to as peptides, 50 – 100 are termed polypeptides, and peptides with over 100 amino acids are generally referred to as proteins.

Hydrolysis (a chemical breakdown of a compound resulting from a reaction with water) can break down a peptide bond. Though the reaction itself is quite slow, the peptide bonds formed within peptides, polypeptides, and proteins are susceptible to breakage when they come into contact with water (metastable bonds).

Energy Release: The reaction between a peptide bond and water releases about 10kJ/mol of free energy.
Absorbance: The wavelength of absorbance for a peptide bond is 190-230 nm.

Structure of the Peptide Bond

Scientists have conducted x-ray diffraction studies of several small peptides to ascertain the physical characteristics of peptide bonds. Such studies have indicated that peptide bonds are rigid and planar. These physical characteristics are principally derived as a result of the resonance interaction of the amide: the amide nitrogen is able to delocalize its sole pair of electrons into the carbonyl oxygen.

This resonance directly affects the structure of the peptide bond. Indeed, the N–C bond of the peptide bond is actually shorter than the N–Cα bond, and the C=O bond is longer than normal carbonyl bonds. In the peptide, the carbonyl oxygen and amide hydrogen are in a trans configuration, not a cis configuration; such a configuration is more energetically favorable due to the possibility of steric interactions in a cis configuration.

The Polarity of the Peptide Bond

Usually, free rotation should be able to take place about a single bond between a carbonyl carbon and amide nitrogen, the structure of a peptide bond. However, the nitrogen in this case has a lone pair of electrons. These electrons are near a carbon-oxygen bond. As a result, a reasonable resonance structure can be drawn, in which a double bond links the carbon and nitrogen.

Consequently, the oxygen has a negative charge and the nitrogen has a positive charge. Rotation around the peptide bond is therefore inhibited by the resonance structure.

-0.28 Oxygen Charge

+0.28 Nitrogen Charge