What is the Difference Between Amide and Peptide Bond

The main difference between amide and peptide bond is in the molecules involved in the bond formation. An amide bond is a chemical bond that occurs between a hydroxyl group of a carboxylic group (-COOH) of one molecule and a hydrogen of an amino group (-NH₂) of another molecule. Whereas, the peptide bond is a type of amide bond which occurs between two amino acids during the synthesis of a polypeptide chain. Furthermore, amide bonds are involved in the formation of small molecules while peptide bonds are responsible for the formation of polymers called proteins.

Amide and peptide bond are two types of chemical bonds that occur between carboxylic and amino groups of molecules.

Key Areas Covered

1. What is an Amide Bond
     – Definition, Structure, Properties
2. What is a Peptide Bond
     – Definition, Structure, Properties
3. What are the Similarities Between Amide and Peptide Bond
     – Outline of Common Features
4. What is the Difference Between Amide and Peptide Bond
     – Comparison of Key Differences

Key Terms

Amide Bond, Amine Groups, Carboxylic Groups, Peptide Bond, Polypeptide Chains

What is an Amide Bond

An amide bond is a type of covalent bond involved in the formation of an amide. An amide is characterized by the presence of a functional group known as RnE(O)xNR′2 (R and R′ refer to H or organic groups). There are three types of amides in nature. They are carboxamides (n = 1, E = C, x = 1), phosphoramides (n = 2, E = P, x = 1 and many related formulas) and sulfonamides (E = S, x = 2). Moreover, the simplest amides are the derivatives of ammonia (RC(O)NH2).

Figure 1: Amides

While considering the basicity, amides are very weak bases in comparison to amines. Therefore, they do not show any acid-base properties in water. Furthermore, amides have a number of technological applications as a structural material. Nylons are such polyamides used in fabric, as fibers, and molds.

What is a Peptide Bond

A peptide bond is a covalent bond which occurs between two consecutive amino acids, forming a polypeptide chain. However, it is also a type of amide bond since it occurs between the carboxylic group of one amino acid and the amino group of the second amino acid. Any of the two amino acids linked by a peptide group is known as a dipeptide. Likewise, polypeptide chains occur due to a sequence of linear peptide bonds. However, due to the presence of a carboxylic group in one end and an amino group in the other end, the polypeptide chain has a polarity.

Figure 2: Peptide Bond Formation

Furthermore, the formation of a peptide bond occurs during protein synthesis with the assistance of ribosomes. These bonds are kinetically very stable; hence, polypeptides will remain for a long period of time in a solution unless any catalyst is present in the solution to degrade it.

Similarities Between Amide and Peptide Bond

• Amide and peptide bond are two types of bonds which occur between the carboxylic groups and amino groups of different molecules.
• The names of these bonds depend on the type of the resultant molecule.
• Both are covalent bonds. They also remove a water molecule.
• Moreover, the resultant molecules of both types of bonds are organic molecules.

Difference Between Amide and Peptide Bond

Definition

An amide bond refers to a compound with a functional group RnE(O)xNR′2 while peptide bond refers to the amide type, covalent chemical bond, which links two consecutive alpha-amino acids. This is the main difference between amide and peptide bond.

Occurrence

An amide bond occurs between a carboxylic group and amino group while a peptide bond occurs between two amino acids.

Type of Molecules Formed

The type of molecules they form is a major difference between amide and peptide bond. Amide bonds help to form small molecules called amides while peptide bonds help to form polymers called polypeptide chains.

Conclusion

An amide bond is a covalent bond which occurs between a carboxylic group of one molecule and an amino group of another molecule. On the other hand, a peptide bond occurs between the carboxylic and amino groups of two amino acids. Amide bonds generally form small molecules while peptide bonds form a polymer called polypeptide chain. Therefore, the main difference between amide and peptide bond is the type of molecules they form.

Reference:

1. Berg JM, Tymoczko JL, Stryer L. Biochemistry. 5th edition. New York: W H Freeman; 2002. Section 3.2, Primary Structure: Amino Acids Are Linked by Peptide Bonds to Form Polypeptide Chains. Available Here

Image Courtesy:

1. “Amide types” By Krishnavedala – Own work (Public Domain) via Commons Wikimedia  
2. “Peptidformationball” By GYassineMrabetTalk This W3C-unspecified vector image was created with Inkscape. – Own work (Public Domain) via Commons Wikimedia