Difference Between Peptide and Dipeptide

The key difference between peptide and dipeptide is that the peptide is a short chain of amino acids that link with each other via peptide bonds whereas the dipeptide is a form of peptide that has either two amino acids joined with single peptide bond or single amino acid with two peptide bonds.

Amino acids are the building blocks of proteins. Therefore, they form peptide bonds with each other forming short chains of amino acids; we call them “peptides”. Long and continuous peptide chains are “polypeptides”. These polypeptide chains link with each other to form proteins. The term peptide is a common term that we use to name a short chain of amino acids, but the term dipeptide is a specific term that we use to name a specific type of peptides.

CONTENTS

1. Overview and Key Difference
2. What is Peptide
3. What is Dipeptide
4. Side by Side Comparison – Peptide vs Dipeptide in Tabular Form
5. Summary

What is Peptide?

The peptide is a short chain of amino acids. These amino acids link with each other via peptide linkages (bonds). The amino acids are thus named as “monomers”. Further, the peptide bonds resemble amide bonds. This bond forms when the carboxyl group of an amino acid react with an amine group of another amino acid. This is a form of condensation reaction in which a water molecule releases when this bond forms. Moreover, it is a covalent chemical bond. There are several names we use along with peptides; dipeptides (contain two amino acids bonded to each other via a single peptide bond), tripeptides (contains three amino acids), etc. In addition to that, polypeptides are long, continuous peptide chains; they are not branched chains, instead, these are polymers.

We can distinguish a peptide from a protein according to its size. Approximately, if the number of amino acids in the peptide is 50 or above, we call it a protein. However, it is not an absolute parameter to distinguish them. For example, we consider small proteins such as insulin as peptides more than as a protein.

Moreover, we name the amino acids that incorporate in peptides as “residues”. It is because of the release of either an H+ ion (from amine end) or an OH- ion (from carboxyl end) during the formation of each peptide bond. Sometimes, they release both ions together as a water molecule. Except for cyclic peptides, all other peptides have an N terminal (amine end) and a C terminal (carboxyl end).

What is Dipeptide?

A dipeptide is a form of peptides that have either two amino acids linked to each other via a single peptide bind or one amino acid having two peptide bonds. Either way, it has two different classes of organic compounds. The two forms are as follows;

1. Two amino acids with single peptide bond – we denote this form as di-X-peptide or X-dipeptide in which “X” designates an amino acid. Some common examples of this type are Carnosine, Anserine, Homoanserine, Kyotrophin, Balenine, Glorin, etc.
2. One amino acid with two peptide bonds – Here, one amino acid contains two minimal peptide bonds. This means the COOH group of C terminal of the peptide becomes COCH₃ while the NH₂ group of N terminal becomes NHCH₃. Ex: alanine dipeptide is CH₃CONHCH(CH₃)CONHCH₃.

A dipeptide forms as a result of the action of hydrolase enzyme, dipeptidyl peptidase. Inside our gastrointestinal tract, the dietary proteins digest into dipeptides and amino acids. Moreover, our body can absorb dipeptides more rapidly than amino acids. This is because their absorption occurs via a separate mechanism.

What is the Difference Between Peptide and Dipeptide?

The peptide is a short chain of amino acids. They contain peptide bonds between amino acids that resemble amide bonds. They may have very complex structures. A dipeptide is a form of peptides that have either two amino acids linked to each other via a single peptide bind or one amino acid having two peptide bonds. They contain either a single peptide bond or two peptide bonds. Moreover, they have a simple structure. The below infographic presents a side by side comparison of the difference between peptide and dipeptide.

Summary – Peptide vs Dipeptide

A dipeptide is a form of peptides. Both of them contains amino acids linked to each other via peptide bonds. The difference between peptide and dipeptide is that a peptide is a short chain of amino acids that link with each other via peptide bonds whereas a dipeptide is a form of peptide that has either two amino acids joined with single peptide bond or single amino acid with two peptide bonds.

Reference:

1. “Peptide.” Wikipedia, Wikimedia Foundation, 27 July 2018. Available here 
2. “Dipeptide.” Wikipedia, Wikimedia Foundation, 27 July 2018. Available here  

Image Courtesy:

1.”Tetrapeptide structural formulae v.1.”By Jü – Own work, (Public Domain) via Commons Wikimedia