Elementary Idea of Peptide Bond

A peptide bond is a covalent link established between two amino acids. Various living creatures use peptide bonds to construct long-chain amino acids or proteins. 

Proteins are a vital biomolecule in human life, as they play a part in nearly every aspect of our existence. Proteins catalyse some most critical events, which provide structural support. In addition, proteins aid in the identification of chemicals in the environment. 

Thus, a peptide bond is the building block for various biological events. Creating peptide bonds is an essential part of existence.

Peptide Bonds

All living cells and viruses rely on proteins to maintain their structure and function. Protein accounts for around half of the dry weight of cells. It is a biopolymer of amino acids linked together by peptide bonds, a high molecular weight organic substance.

A condensation process (or dehydration synthesis) happens when two amino acids come into contact with one other. The carboxyl (CO) and amino (NH) groups react with each other to form a peptide bond. The reaction produces the amide or peptide molecule [C(=O)NH] releases water (H2O).

The peptide bonds hold together polypeptides and proteins. They form the backbone of DNA.

Types of Compounds formed by Peptide Bonds

One can divide amino acids into the following categories according to the number of peptide connections.

• Dipeptides: 

When two amino acids react with one another, they form dipeptides. Because a dipeptide is composed of two amino acids, the chemical reaction is referred to as a reaction of dipeptides. The carboxyl group of glycine can interact with the amino group of alanine to form the dipeptide glycylalanine.

• Tripeptide: 

When a third amino acid is added to a dipeptide using another peptide bond, the resulting product is known as a tripeptide. It comprises three amino acids that are joined together by two peptide links.

• Polypeptide: 

The term “polypeptide” refers to molecules that include more than ten amino acids and two peptide connections. As the name implies, protein is a polypeptide containing more than one hundred amino acid residues and a molecular mass of more than 10,000u.

Peptide Bond Formation or Synthesis of Peptide Bonds

Dehydration synthesis or reaction, also known as condensation reactions, creates peptide bonds at the molecular level. The presence of amino acids is a characteristic of the process.

Two amino acids are more likely to connect following after removing oxygen and two hydrogen molecules. They contribute the carboxyl group to this process, whereas they deplete the hydroxyl group. Proteins that include amino groups derived from various amino acids deplete their hydrogen content. 

A peptide bond is produced due to the substitution of nitrogen for the hydroxyl group after that. For this reason, peptide bonds are substituted amide connections. 

The amino acids employed in the peptide bond formation process are referred to as residues after the reaction because they lose many atoms and become covalently bound to one another due to the creation of a peptide bond after completing the reaction.

The nitrogen to carbon link created in the peptide bond is notably distinct from the nitrogen-carbon bonds found in the various other molecule sections. Nitrogen has a positive charge on the carboxyl bond side, whereas oxygen is negative. 

Considering that the negative and positive charges are both minor, this interaction leads to the nitrogen and carbon sharing more electrons than how much they share. The formation of an electric dipole is the result of the entire operation.

With the addition of extra electrons, the bond serves as a double bond, which is very inflexible and cannot spin. A peptide group is a six-molecule unit that appears in a flat plane or a ball. Peptides are present in all living things. 

In addition to having four equal bonds, the carbons present in the centre of amino acids can spin freely. Thus, when a peptide bond forms between numerous amino acids, a chain of unbending atom planes is formed around the peptide bond to provide structural support. 

The flexible bonds of carbon properly connect it. Peptide chains can bend and spin due to this whole environment, producing very sophisticated creations that have the power to catalyse chemical pathways.

Hence, the ensuing CO-NH bond is called the peptide bond, and the resulting molecule is known as an amide (CO-NH).

Degradation of Peptide Bond

During peptide bond degradation, the molecules’ peptide bonds are broken, resulting in the formation of new peptide bonds. For the breakdown of peptide bonds, hydrolysis (the addition of water) is utilised as a reaction. They potentially emit Gibbs energy in the range of 8-16 kJ/mol during the reaction. 

At a temperature of 25oC, this is a prolonged process with a half-life of 350 to 600 years for each bond in most cases. The employment of enzymes such as proteases as catalysts aid this process.

Note:

1. Heating or a high salinity will not cause peptide bonds to break down. Only exposure to a strong base or acid at high temperatures for an extended period can denature them. In addition, the process requires the involvement of digestive enzymes. 
2. Peptide bonds help maintain proteins’ structure due to their rigidity and planarity. They have both partial positive charge groups (due to hydrogen atoms of amino groups) and partial negative charge groups (due to oxygen atoms of carboxyl groups).

Conclusion

A peptide bond is a covalent bond generated between two amino acids. Various living things use peptide bonds to generate long-chain amino acids or proteins.

Proteins are essential for the construction and function of all living cells and viruses. Protein makes up almost half of a cell’s dry weight. It is a high-molecular-weight organic molecule composed of a biopolymer of amino acids connected by peptide bonds.