What is the Difference Between Peptide and Protein

The main difference between peptide and protein is that peptide is a short sequence of amino acids with a primary structure whereas protein is a polypeptide, a much larger structure with different levels of organization such as secondary, tertiary, and quaternary structures. Furthermore, peptide bonds occur between amino acids in the polypeptide chain while different polypeptide chains of a protein are connected by hydrogen bonding, disulfide bridges, etc. 

Peptide and protein are two types of structures made up of amino acids. Generally, they are essential organic compounds that perform various functions inside the cell. 

Key Areas Covered 

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

Key Terms 

Peptide, Polypeptide, Primary Structure, Protein, Secondary Structure, Sequence of Amino Acids 

What is a Peptide 

A peptide is a simple molecule composed of less than 50 amino acids. Furthermore, a polypeptide is an amino acid chain with 10 to 100 amino acids while polypeptides with more than 50 amino acids are the proteins. Basically, there are two types of peptides, depending on the number of amino acids. They are oligopeptides, which contain 2-10 amino acids, and polypeptides, which contain 10-50 amino acids.

Figure 1: A Tetrapeptide

Furthermore, each amino acid is attached to the chain through a peptide bond. Since peptides have a fewer number of amino acids, they are linear molecules. In general, the biological function of peptides is to regulate the activities of other molecules. 

What is a Protein 

A protein is one of the four types of biological macromolecule found in the body. It is composed of a series of amino acids, determined by the information encoded in the corresponding gene. Protein synthesis occurs through two steps: transcription and translation. The bonds that link amino acids together are peptide bonds.  

Moreover, the primary, secondary, and tertiary structures of a protein consist of a single polypeptide chain. However, in the primary structure, this polypeptide chain is linear. In order to form the secondary structures such as alpha helices and beta sheets, the primary structure forms hydrogen bonds between amino acids. They also form tertiary structures such as globular proteins and filamentous proteins through the formation of hydrophobic and hydrophilic interactions, hydrogen bonds, ionic bonds, disulfide bridges, etc. Ultimately, the association of two or more polypeptide chains form the quaternary structure of proteins.

Figure 2: Protein Structure

Proteins perform various functions in the body. Usually, they take part in the formation of structures, including muscle, cartilages, hair, nails, and cell membrane components. Moreover, most globular proteins serve as enzymes, hormones, and transport proteins in the blood. Other globular proteins called antibodies serve as key molecules in the immune system.  

Similarities Between Peptide and Protein  

• Peptide and protein are two types of organic compounds that occur in a  cell.  
• Both are made up of amino acids.  
• Moreover, peptide bonds occur between amino acids of each type of compound.  
• They also undergo posttranslational modifications such as phosphorylation, hydroxylation, sulfonation,  palmitoylation, glycosylation, etc.  
• They perform specific functions inside the cell. 

Difference Between Peptide and Protein 

Definition 

A peptide refers to a short chain of amino acids that are connected to one another in a sequence by a peptide bond while a protein refers to a polymer of amino acids with a variety of functions inside the cell. 

Number of Amino Acids 

Moreover, a peptide is a short chain of amino acids, containing approximately 50 or fewer amino acids, while a protein is a polypeptide, containing more than 50 amino acids. 

Types of Amino Acids 

While peptides are composed of both essential amino acids and other naturally-occurring amino acids, proteins only are composed of 20 essential amino acids. 

Structural Organization 

Peptides have a primary structure of a protein, mainly being a straight chain of amino acids although lariat structures have been observed. In contrast, proteins have either secondary, tertiary or quaternary structure. 

Bonds 

Also, peptide bonds occur between amino acids while hydrogen bonds, disulfide bonds, etc. occur between polypeptide chains of amino acids.  

Function 

Furthermore, functionally, peptides play a key role in regulating activities of other molecules, especially proteins, while proteins serve as structural molecules, enzymes, hormones, etc. 

Conclusion 

A peptide is a short chain of amino acids. Generally, it contains less than 50 amino acids. It can contain both essential amino acids and other naturally-occurring amino acids. Peptides, on the other hand, have a linear structure. But, a protein is a polypeptide, containing more than 50 amino acids. Proteins can also have either secondary, tertiary or quaternary structures. However, they only contain essential amino acids. Basically, proteins play a structural and regulatory role in the cell while peptides regulate the functions of proteins. Therefore, the main difference between peptide and protein is their size, shape, and function. 

References:

1. “Peptide.” Nature News, Nature Publishing Group, Available Here.
2. Szalay, Jessie. “What Is Protein?” LiveScience, Purch, Available Here.

Image Courtesy:

1. “Tetrapeptide structural formulae v.1” By Jü – Own work (Public Domain) via Commons Wikimedia   
2. “Main protein structure levels en” By LadyofHats – Own work (Public Domain) via Commons Wikimedia