While peptides and proteins are fundamentally the same as one another – both a chain of amino acids held together by peptide bonds – they do, in fact, have subtle differences. And these extend beyond just the length. Take a look below at how the two differ in structure, function and therapeutic application.

What are peptides?

Peptides are chains of amino acids — the building blocks of proteins — that are naturally found in your body. According to the National Human Research Institute, they typically comprise between two and 50 amino acids and are characterised by a central carbon atom, an amino group, a carboxyl group and a unique side chain. 

There are two types of peptides: endogenous and exogenous. The former is produced within various cell types throughout your body, ranging from neural cells to immune system cells. Every protein in your body consists of a solitary chain comprising 20 or more amino acids, referred to as a polypeptide. 

Within these chains, amino acids are intricately arranged in a specific sequence, a configuration that dictates the peptide’s unique function and structural characteristics. 

Peptides play crucial roles in various biological processes. According to the National Library of Medicine, they can act as hormones, neurotransmitters, enzymes, or signalling molecules, influencing a wide range of physiological functions in organisms. For instance, insulin is a well-known peptide hormone that regulates blood sugar levels, while endorphins are peptides that function as natural painkillers.

Exogenous peptides, however, are peptides that have entered your body from the outside, such as food, cosmetics, supplements and medications.

What are proteins?

According to the National Human Genome Research Institute, proteins are complex, versatile molecules that serve as the fundamental building blocks of life and play an integral role in nearly all biological processes. They are composed of long chains of amino acids, linked together by peptide bonds. A typical protein may consist of hundreds or even thousands of these amino acids.

The specific structure and sequence of amino acids within a protein determine its unique function. Any alteration in this sequence can lead to changes in protein function, which can have profound effects on an organism’s health and well-being. In essence, proteins are the workhorses of biology, driving the many processes necessary for life.

Proteins serve a multitude of critical functions in living organisms. They can act as enzymes, catalysing biochemical reactions, and as structural components, providing stability to cells and tissues. Proteins are also involved in cell signalling, immune responses and the transport of molecules within the body. Haemoglobin, for example, is a protein responsible for transporting oxygen in the blood.

What are the benefits of peptides and proteins?

Peptides and proteins offer numerous benefits, particularly in health and wellness. Peptides play a key role in regulating various biological functions, such as hormone production, immune response, and cellular repair. Proteins, made up of long chains of amino acids, are essential for building and repairing tissues, supporting enzyme activity, and maintaining immune function. Both peptides and proteins are integral to muscle growth, skin health, and overall bodily functions, making them vital for both therapeutic and nutritional applications.

What are the differences between peptides and proteins?

While they may appear to be the same thing on the surface, these two chains have crucial distinctions that are important to know. In fact, understanding the differences between a peptide and a protein is fundamental for comprehending their roles in biological processes and therapeutic applications. 

Structure

Research has shown that the primary structural difference between peptides and proteins lies in their size. Peptides are relatively small, typically consisting of fewer than 50 amino acids, while proteins are larger, often comprising hundreds or even thousands of amino acids. 

As a result, their size disparity impacts their complexity and function. Proteins possess intricate three-dimensional structures, consisting of multiple folded regions called domains, which enable them to perform diverse biological roles. Peptides, being smaller, have simpler structures, with limited folding. 

This difference in size and complexity underlies the variations in their functions, as proteins often serve as enzymes, receptors or structural elements, while peptides frequently function as signalling molecules or hormone precursors.

Function

According to the Institute for Molecular Bioscience, proteins, due to their larger size and complex three-dimensional structures, often serve as catalysts (enzymes), catalysing biochemical reactions; providing structural stability to cells and tissues; facilitating cell signalling and communication; and participating in immune responses and molecular transport, making them essential for life’s diverse functions.

In contrast, peptides typically function as signalling molecules or hormone precursors in biological processes. They play crucial roles in cellular communication, regulating physiological functions and initiating specific responses. Peptides can interact with cell receptors, modulate gene expression, and orchestrate various biochemical activities, making them integral components of intercellular communication and regulating numerous biological functions in organisms.

Therapeutics

Typically, the shorter the protein, the more unstable it will be. Because of this, peptides have fewer therapeutic applications than proteins. That said, peptides boast a low specificity and risk of side effects, allowing them to serve as drug candidates in fields like diabetes, pain management and hormone regulation. 

Peptide-based vaccines and antimicrobial peptides are also under development for infectious diseases. Their targeted nature and ability to modulate specific pathways make proteins and peptides promising tools in modern therapeutics.

Proteins, on the other hand, with their diverse structures and functions, are used for enzyme replacement therapy for genetic disorders (e.g., in lysosomal storage diseases), as monoclonal antibodies for cancer immunotherapy and as clotting factors for haemophilia treatment. They are also employed in vaccines, cytokine therapies and hormonal replacements (e.g., insulin). 

What are the similarities between peptides and proteins?

But despite all these differences, research has shown that peptides and proteins share several fundamental similarities. Both are made up of amino acids linked by peptide bonds, forming linear chains. Because of this, they are essential biomolecules involved in various biological processes, including cellular signalling, enzymatic reactions and structural support. In fact, their three-dimensional structures, driven by folding and interactions among amino acid side chains, underlie these biological activities. 

While their therapeutic applications may differ, they both undergo post-translational modifications such as phosphorylation, hydroxylation, sulfonation, palmitoylation, glycosylation and more. 

Ultimately, peptides can be considered smaller counterparts to proteins, with both classes of molecules playing essential roles in the complex machinery of life.

In a rapidly evolving scientific landscape, the study of peptides and proteins continues to unravel the mysteries of life while offering solutions to some of the biggest challenges in modern medicine. With some of the leading scientists and cutting-edge technologies hard at work, we are moving ever closer to unlocking new opportunities in the world of peptides and proteins, revolutionising healthcare, biotechnology and beyond.

Here at Bachem, we have produced an online peptide guide which covers all the essential topics like peptide synthesis methods, purification techniques and peptide modifications. If you’re looking to further enhance your understanding, this guide will serve as an essential resource.

Looking for a convenient tool to determine peptide molecular weight? Try our helpful peptide calculator today.