Peptide comes from the Greek word “peptos” which means digested. Amino acids are linked together by amide bonds to form a short chain, and these natural short chains are called peptides. Hormones and antibiotics are included in peptides. Protein and peptides both are segregated according to size.
Peptides can be of different types. They are classified according to the constituents of amino acids. If there are less number of amino acids, the peptides will be shorter. Whereas, if there are more number of amino acids, the peptides will be longer. The peptides with more number of amino acids are called long peptides.
Emil Fischer, known as the father of peptides, originated the term peptide. Peptides are unbranched. A polypeptide is a type of a peptide and is known as a long peptide. Polypeptides consist of a series of amino acids. Oligopeptides and polypeptides are the main peptides.
What are peptides?
The linkage of amino acids by amide bonds forms short chains, which are natural short chains, called peptides. A peptide bond is smaller than a single bond and larger than a double bond. Since it has the characteristic of a partial double bond it can avoid a polypeptide free rotation. A Peptide bond has the ‘trans’ symmetry and can not be ‘cis’ because of steric hindrance.
Complex structures of peptides comprise more than 50 amino acids. Generally, we can say that peptides are the shorter kind of proteins.
The sources of peptides are eggs, milk, meat, fish, beans, soy, oats and wheat. While linking amino acids, water molecules can be removed.
Types of peptides
Peptides are mainly of three types. They are also classified according to their functions.
Ribosomal peptides
Generally, ribosomal peptides can be produced through proteolysis – a process in which protein is broken down into peptides or amino acids. Examples: antimicrobial peptides, pancreatic polypeptides.
Peptones
Peptones are synthesised during proteolysis of milk and meat. It is mainly used for growth of fungi and bacteria.
Milk peptides
Digestion of milk protein leads to the formation of milk peptides.
Dipeptides
In dipeptides, two amino acids are linked together by one peptide bond.
Example: carnosine, anserine
Tripeptides
In tripeptides, three amino acids are linked together by two peptide bonds.
Example: glutathione
Oligopeptides
In oligopeptides, there are more than two and less than 20 amino acids linked together by peptide bonds. Dipeptide, tripeptide, and tetrapeptide also come in the form of oligopeptides.
Example: netropsin
Polypeptides
Polypeptides are the longest peptides known, and hence they are called long peptides. In polypeptides, there is a linkage of amino acids. They help in cell function.
Functions of peptides in the body
Peptides have many important functions:
- They are the parent of proteins.
- They act as hormones. Example- vasopressin, insulin.
- They also behave as growth factors.
- They help to support the body.
- They can promote cells.
- They are strong and have partial double bonds.
What are long peptides?
Polypeptides are known as long peptides. These long peptides are used to form proteins by linkage of various amino acids. Polypeptides are mainly composed of almost 50 amino acids, and hence they are known as long peptides. The linkage of two or more polypeptides forms a complex structure of proteins.
Long peptides are synthesised during the process of protein synthesis. Long peptide synthesis is a process used in making oligopeptides and proteins. The long peptides contribute to the primary or secondary structures of protein.
The major limitation faced in the synthesis of long peptides is the cumulative effect of the yield.
Long peptides are a secondary structure of proteins. In contrast to proteins, long peptides are simple in structure. Long peptides are used for structural scanning in different techniques such as electron paramagnetic, resonance, NMR, x-ray crystallography.
Example: natriuretic peptide, DNP
Conclusion
The chain of amino acids are called peptides. The linkage of amino acids by amide bonds forms a short chain called peptide bonds. For linkage water is removed. Protein can be known as longer peptides or peptides can act as a parent of protein. Peptides are building blocks of hormones, enzymes, and cells.
Peptides and proteins are quite different as not all peptides form proteins, but all proteins consist of peptides.
Peptides have a simpler structure than proteins. When there is a linkage of 50 or more amino acids, it is called a long peptide. Polypeptides are also known as long-chain peptides. The synthesis of long peptides mainly takes place during the process of protein synthesis.
The main issue in synthesising long peptides is contamination during the assembly of peptides. Many functions are shown by peptides, such as peptides can act as hormones or have vital roles in various hormones (example- insulin, vasopressin). Long peptides act as a growth factor and provide support to the body.