Peptide Bond vs Ester Bond: Comparative Analysis And Facts

In this article ” Peptide Bond vs Ester Bond” the similarities and differences between these two bonds are clarified specifically.

Subject Peptide Bond Ester Bond
Connection between Peptide bonds connect two amino acids Ester bond connects an alcohol with an carboxylic acid.
Function Peptide Bond forms protein / polypeptide Ester linkages are backbone of lipid molecules
Formation Peptide bond is formed through condensation reaction between two amino acids Ester bond is also formed between alcohol and acid molecule due to condensation reaction
Participating  atoms Nitrogen atom from one amino acid forms the peptide linkage with the carbon of carboxylic group from another amino acid. In ester bond, an oxygen atom is bound with the carbon atom of any alkyl or aryl group.

Ester bond is a type of chemical bond, that helps to join alcohol group with carboxylic acid group in the presence of catalyst ,but peptide bond is a type of chemical covalent bond that is formed between the reaction of two successive α amino acid. Similarities and differences between these two bonds are pointed out in this article.

Definition of Ester Linkage and Peptide Linkage

The ester linkage is formed when a carboxylic acid group (COOH) from a molecule and an alcohol group(OH) from another different molecule participate in a reaction in the presence of concentrated acid ( act as catalyst) and eliminate one water (H2O) molecule. One of the important ester linkage present in living organism is formed between the oxygen molecule of glycerol and hydroxyl group comes from fatty acid.

Peptide bond is mainly a covalent chemical bond which is called amide (-CONH2) type bond present in protein. It is formed by linking  two consecutive alpha amino acids. In the formation of peptide bond, amine group (NH2) from one amino acid reacts with the carboxylic acid group (COOH) of another amino acid and one water molecule is removed.

peptide bond vs ester bond
Ester Linkage. Image Credit: Wikimedia Commons
peptide bond in dna 1
Peptide Bond. Image Credit: Wikimedia Commons

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Ester Bond in Lipid

One of the most well known lipid in biology is ‘glyceride”. A glyceride consists of glycerol and fatty acid, and these two groups are bound by the ester linkage. Fatty acid is stored in the form of glyceride by reacting with glycerol molecule. Another example of familiar lipid is “phospholipid” ,a group of polar lipids  that basically contains a glycerol molecule attached with phosphate group (PO43-) and two “hydrophobic  tails”, derived from fatty acids. These groups are joined by alcohl residue (glycerol molecule).

0301 Phospholipid Structure new
Ester Bond in Phospholipid Image Credit: Wikimedia Commons

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Some Frequently Asked Questions (FAQ)

Is a Peptide Bond an Ester Bond?

There is a basic different between a peptide bond and an ester bond, discussed below.

Peptide bonds are one type of amide (-CONH2) bond and exclusively primary structure. It basically connects two consecutive amino acids. In  formation of a peptide bond nitrogen atom from one amino acid is bonded with the carbon atom from the carboxylic group present in the other amino acid.

Ester bond is one type of intramolecular chemical covalent bond. They are described as a carbon is linked with another three atoms: a sigma bond (single bond) with a carbon, a pi bond (double bond) with an oxygen and a single bond with another oxygen atom. Ester groups or ester bond is derived from parent acid ( carboxylic acid) and parent alcohol. Esters are written as RCOOR in organic chemistry.

Esters formation
Ester Bond Formation. Image Credit : Wikimedia Commons

In peptide bond, due to delocalization of unshared electron pair, C-N bond possesses partial double bond character. This bond is not flexible and free rotation about this bond is become restricted. Whereas ester bond contains a carbonyl center (C=O) and the C-C-O and O-C-O bond angle becomes 1200.  The unshared pair of electrons from oxygen can not participate in resonance because , after sharing the electron pairs oxygen becomes partially positive and it will not be feasible as oxygen is more electronegative than nitrogen. Thus it behaves as single bond and possesses sp2 hybridization and structurally flexible because of the rotation of C-O-C bond.

Ester bonds are the backbones of lipids and peptide bonds are the key components o protein.

Basically ester bonds are formed due to the condensation reaction between carboxylic acid group (COOH) and hydroxyl groups (OH) of one acid and alcohol. On the other hand, peptide bond is formed due to the condensation reaction between amine (NH2) and carboxyl group (COOH) of two consecutive α amino acid. Therefore both these bonds are formed through condensation reaction.

From the above discussion, it is clearly shown that, peptide bond is totally different from ester bond in structure, geometry, participating atoms.

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Is Peptide Bond Stronger Than Phosphodiester Bond?

Peptide bond is stronger than the ester bond.: Why peptide bond is stronger than ester linkage” is discussed clearly in this point.

From the study between these two bonds, it is proved that peptide bond is stronger than ester bond. Peptide bonds have some double bond character due to presence of unshared electron pair but ester bonds are structurally flexible with respect to peptide bond. In ester the C-O-C bond contains lower energy barrier than peptide bond.

The basic difference between these two bonds are C-N bond in peptide linkage is replaced by the C-O linkage in ester. The average bond dissociation energy of C-O bond is 358 KJ/mol and C-N bond is approximately 293 KJ/mol. From the thermodynamic point of view of the hydrolysis of the peptide bond, the Gibbs free energy released is 2-4 kcal/mol (8-16 KJ/mol)  and for ester  bond it is 5.3 kcal/mol (22.26 KJ/mol).

The hydrolysis reaction of a peptide bond is not favored and the half life is 350-600 years per bond at 298K (250C) due to the presence of partial double bond character in peptide bond.

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