Peptides

What are Peptides?

Peptides are short chains of amino acids. In peptides, two or fifty amino acids get linked by peptide bonds. 

When two consecutive - amino acid molecules get linked together by removal of one water molecule and by formation of covalent between C1 of one - amino acid and N2 of another - amino acid, then this type of covalent bond is called peptide bond. Peptide bond formation is given below –

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Thus, we can say peptides are formed by linking two and fifty amino acids by peptide bonds and removal of water molecules. 

Word peptide has been taken from Greek word peptos , which means ‘digested’. 

Chains of peptides which contain less than ten or fifteen amino acids are called oligopeptides. Dipeptides, tripeptides and tetrapeptides etc. come under the class oligopeptides only. 

Polypeptides are long, unbranched chains of peptides up to approximately 50 amino acids. Peptides are essential for proper functioning of cells. These are also studied under the molecular biology. They come under the class of biological polymers, nucleic acids, oligosaccharides, polysaccharides, and oligomers. 

Although peptides and proteins are the same as both are made up of amino acids, but the peptide chains are shorter than proteins. When a polypeptide contains more than 50 amino acids then it is known as protein. 

All peptides have an N – terminal and C – terminal residue at the ends of the peptide chains. Cyclic peptides are exceptions in this case. N – terminal represents the start of polypeptide and referring to the free amine group. C – terminal represents the end of the polypeptide chain and referring to the free carboxyl group. 

Types or Classes of Peptides 

Peptides have been classified according to their sources and functions. Few of its main classes have been discussed below –

• Ribosomal Peptides – Ribosomal peptides are subjected to proteolysis. They function in higher organisms as hormones. These are of many types such as antimicrobial peptides, tachykinin peptides, vasoactive intestinal peptides, pancreatic polypeptide etc. 

• Peptones – They are formed during the proteolysis of milk and meat. They are used for growing fungi, bacteria for various purposes. 

• Milk Peptides – These are formed by digestion of milk protein. They also formed during fermentation of milk. 

• Dipeptides – These peptides are formed by linkage of two amino acids by one peptide bond. Example – carnosine, anserine etc. 

• Tripeptides – These peptides are formed by linkage of three amino acids by two peptide bonds. Example – glutathione, ophthalmic acid etc. 

• Oligopeptides – These peptides are formed by linkage of more than two and less than 20 amino acids by peptide bonds. Example – netropsin, amanitin etc. 

On the basis of number of amino acids peptides can be of many types such as monopeptide, dipeptide, tripeptide (as discussed above), tetrapeptide, pentapeptide, hexapeptide, heptapeptide, octapeptide, nonapeptide and decapeptide. 

Formation of Peptides 

Peptides are formed by the peptide linkage between amino acids. let us understand the peptide formation by taking an example of dipeptide. For the formation of dipeptide, two amino acids approach each other and form a covalent bond between C₁ – carbon of carboxylic acid and N₂ – nitrogen atom of amino acid group by removal of the water molecule. One amino acid loses its hydrogen atom and another its hydroxyl group. It is a condensation reaction. The covalent linkage formed between two amino acids is called peptide bond (-CO-NH-) or peptide linkage. Formation of peptide bonds consumes energy. As the water molecule is getting removed, so it is a dehydration synthesis process. 

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Formation of a Dipeptide

When these peptide bonds of peptide break, they release energy. These can be broken down by hydrolysis, but it is a very slow process. Enzymes such as peptidases or proteases can catalyze the process. 

Although peptide and protein both are composed of amino acids and carry out various important functions in cells but differ in their various aspects. Difference between peptide and protein is given below –

Difference Between Peptide and Protein 

Functions of Peptides

Peptides are fundamental organic compounds of cells. They carry out various important functions in the cell. In human body, they perform key roles in various biological reactions. Few of its functions are listed below –

• They are important for muscle building. 

• GHRP 6 (Growth hormone releasing peptide 6) is useful in the growth of our body. 

• Neuropeptides are used by neurons to communicate with each other. 

• Various peptides act as hormones such as peptide hormone.

• Opioidergic agent is a peptide which functions to directly modulate the opioid neuropeptide systems in the brain. 

• Copper – peptides are useful for flawless skin and protection against harsh sunny conditions. 

• Some peptides are used for hunger issues as well.

• They are used for healing purposes as well. 

• They are useful in increasing the level of prolactin hormone in females. 

• They function as antibiotics and prevent the growth of microorganisms. 

• They work as anticancer agents as well. Although many evidences are not there to support that peptides have an active role as anticancer agents.

• They play a role of mediator in various reactions.

• Some peptides work as a transporter. They selectively allow certain molecules to pass through the cell membrane. 

This ends our coverage on the topic “Peptide”. We hope you enjoyed learning and were able to grasp the concepts. We hope after reading this article you will be able to solve problems based on the topic. If you are looking for solutions of NCERT Textbook problems based on this topic, then log on to Vedantu website or download Vedantu Learning App. By doing so, you will be able to access free PDFs of NCERT Solutions as well as Revision notes, Mock Tests and much more.