Peptide Bond—What Is It?
A peptide bond refers to the covalent bond that gets created by two amino acids. For the peptide bond to occur, the carboxyl group of the first amino acid will need to react with an amino group belonging to a second amino acid. The reaction leads to the release of a water molecule.
It’s this reaction that leads to the release of the water molecule that is commonly called a condensation reaction. From this reaction, a peptide bond gets formed, and which is also called a CO-NH bond. The molecule of water released during the reaction is henceforth known as an amide.
Formation of a Peptide Bond
For the peptide bond to be formed, the molecules belonging to these amino acids will need to be angled. Their angling helps to ensure that the carboxylic group from the first amino acid will indeed get to react with that from the second amino acid. A simple illustration can be used to show how the two lone amino acids get to conglomerate via a peptide formation.
Their combination results in the formation of a dipeptide. It also happens to be the smallest peptide (it’s only made up of two amino acids). Additionally, it’s possible to combine several amino acids in chains to create a fresh set of peptides. The general rule of thumb for the formation of new peptides is that:
- Fifty or fewer amino acids are known as peptides
- Fifty to a hundred peptides are called polypeptides
- Any formation having more than a hundred amino acids is typically regarded as a protein
You can check our Peptides Vs. Proteins page in the peptide glossary to get a more detailed explanation of proteins, polypeptides, and peptides.
A peptide bond can be broken down by hydrolysis (this is a chemical breakdown process that occurs when a compound comes into contact with water leading to a reaction). While the response isn’t fast, the peptide bonds existing within proteins, polypeptides, and peptides can all break down when they react with water. The bonds are known as metastable bonds.
When water reacts with a peptide bond, the reaction releases close to 10kJ/mol of free energy. Each peptide bond has a wavelength absorbance of 190-230 nm.
In the organic universe, enzymes contained in living organisms are capable of forming and also breaking the peptide bonds down.
Various neurotransmitters, hormones, antitumor agents, and antibiotics are classified as peptides. Given the high number of amino acids they contain, many of them are regarded as proteins.
The Peptide Bond Structure
Researchers have completed x-ray diffraction studies of numerous tiny peptides to help them determine the physical attributes possessed by peptide bonds. The studies have shown that peptide bonds are planer and rigid.
The physical appearances are predominantly a consequence of the amide resonance interaction. Amide nitrogen is in a position to delocalize its singular electrons pair into the carbonyl oxygen. The resonance has a direct effect on the peptide bond structure.
Undeniably, the N-C bond of each peptide bond is, in fact, shorter compared to the N-Ca bond. It also happens that the C=0 bond is lengthier compared to the ordinary carbonyl bonds.
The amide hydrogen and the carbonyl oxygen in a peptide are in a trans configuration, as opposed to being in a cis configuration. A trans configuration is considered to be more dynamically encouraging because of the possibility of steric interactions when dealing with a cis configuration.
Peptide Bonds and Polarity
Usually, free rotation ought to occur around a given bond between amide nitrogen and a carbonyl carbon, the peptide bond structure. But then again, the nitrogen referred to here only has a singular pair of electrons.
The lone pair of electrons is located close to a carbon-oxygen bond. For this reason, it’s possible to draw a reasonable resonance structure. It’s a structure where a double bond is used to link the nitrogen and the carbon.
As a result, the nitrogen will have a positive charge while the oxygen will have a negative one. The resonance structure, thereby, gets to inhibit rotation about this peptide bond. Furthermore, the material structure ends up being a one-sided crossbreed of the two forms.
The resonance structure is deemed an essential factor when it comes to depicting the actual electron distribution: a peptide bond contains around forty per cent double bond character. It’s the sole reason why it’s always rigid.
Both charges cause the peptide bond to get a permanent dipole. Due to the resonance, the nitrogen remains with a +0.28 charge while the oxygen gets a -0.28 charge.
A peptide bond is, thus, a chemical bond that occurs between two molecules. It’s a bond that occurs when a carboxyl cluster of a given molecule reacts with an amino set from a second molecule. The reaction eventually releases a water molecule (H20) in what is known as a condensation reaction or a dehydration synthesis reaction.