Peptides: What They Are and How They Are Different From Proteins

A peptide refers to a chain of amino acids linked together by peptide bonds. The bonds are covalent in nature and they are formed when the carboxyl groups of two different amino acids react with one another, displacing a water molecule in the process. Peptides are part of nature and there are thousands of them occurring naturally in plants, animals as well as in human beings. However, in addition to the natural occurrence of peptides, the advancements in technology have led to the discovery of new synthetic ones. This is very promising for the future of health and drug development. Peptides have very beneficial roles in health, and currently, there are a plethora of studies underway to continue understanding more about peptides as well as finding new uses for them in fields such as neurological function, skin care, anti-aging, and many others.

How peptides are made

Peptides can be made naturally as they are already occurring in nature, animals and in human beings and they can also be made artificially through a process known as peptide synthesis. Both non-ribosomal peptides and ribosomal peptides are made outside the organism. Manufactured peptides, also known as synthetic peptides are made through a process known as solid-phase peptide synthesis or liquid-phase peptide synthesis. With both processes, it is possible to get the maximum requested purity, as different studies and research will always require peptides with different purities. With most custom peptide synthesis suppliers today, peptide synthesis is available in a number of sequences and lengths.

The differences between peptides and proteins

Peptides and proteins share the same building blocks – amino acids, though they are very different in terms of structure and functions in the body. Most people don’t know how to tell the difference between the two, however, distinguishing them is relatively easy if you know what to look for. The major difference between the two is their size. The rule of thumb is that a peptide has a sequence of 50 amino acids or less. A polypeptide chain refers to long, unbranched amino acids that come together to form a peptide chain. A protein, on the other hand, has one or more polypeptides which have been arranged in a biologically functional manner. In most cases, proteins are joined to other proteins or other complex molecular structures such as RNA and DNA. Certain proteins, such as insulin may sometimes be referred to as peptides, when structurally, they are not peptides.

About amino acids in peptides

Amino acids are important biological molecules needed in the living organism for a number of applications. Only 20 amino acids are required by the human body to function normally, though there are over 500 amino acids which have already been identified in the universe. The 20 amino acids required by the human body are referred to as essential amino acids, and without them, certain body functions would be affected.

An amino acid is comprised of a carboxylic acid group and an amide group at either end of its structure. Due to this structure, amino acids are cut for certain functions as well as very specific interactions with different molecules within the organism.

Many people think of amino acids as nothing but certain parts of proteins, but they perform very vital functions in the body. They are the building blocks for proteins and operate as intermediaries in a number of metabolic reactions. They may work individually or in conjunction with hormones and are used to transfer energy to the various parts of the body where the energy is needed.

The number of amino acids in peptides

The shortest peptide has only two amino acids and they are referred to as dipeptides. Peptides with three or four amino acids are referred to as tripeptide and tetrapeptides respectively. This is the naming convention used to name the peptide – the name is thus dependent on the number of amino acids in the peptide. As such, we have undecapeptide (11 amino acids), dodecapeptide (12 amino acids), tridecapeptide (13 amino acids), icosapeptide (20 amino acids), tricontapeptide (30 amino acids), and so on.

The different types and classes of peptides

There are different types of peptides available today – both natural and artificial. Here is a brief look at some of the types and classifications of peptides:

· Milk peptides– these are peptides obtained from milk. They are formed in the process of digestion when the digestive enzymes break down – a milk protein. They can also be formed during the process of milk fermentation.

· Ribosomal peptides– these peptides don’t occur naturally, but are synthesized following the translation of mRNA. To get more mature forms of ribosomal peptides, they are sometimes subjected to a process known as proteolysis.

· Non-ribosomal peptides– these peptides feature enzymes unique to each other rather than using ribosomes in the process. A common non-ribosomal peptide is a glutathione and most of these peptides are highly complex with structures that are often cyclic in nature.

· Peptide fragments– these refer to fragments of proteins which are used to identify or quantify the source of proteins present in a given peptide. In other words, they are used to determine the data related to the source proteins. In most cases, they are available as products of enzymatic degradation due to processes conducted in the laboratory or other controlled environments.

· Peptones – peptones are a result of proteolytic digestion and they are obtained from the digestion of meat or milk.

Peptides vs Proteins

Both peptides and proteins are made from amino acids brought together by peptide bonds, but not all peptides are proteins and not all proteins are peptides. The difference between the two lies in their structure. Proteins, for example, can fold back to form detailed structures with specific biological functions. Peptides, on the other hand, cannot fold themselves but they can still perform a number of biological functions. The rule of thumb is that peptides are composed of 50 or fewer amino acids while proteins may contain more than that.