Peptides are short chains of between two and fifty amino acids linked by peptide bonds .   Chains of less than ten or fifteen amino acids are called oligopeptides , and include dipeptides , tripeptides , and tetrapeptides . A polypeptide is a long, continuous, non-branched peptide chain of up to about fifty amino acids.  Therefore, peptides fall under the broad chemical classes of biological polymers and oligomers , along with nucleic acids , oligosaccharides , polysaccharides , and others.
A polypeptide consisting of more than fifty amino acids is known as a protein .    Proteins consist of one or more polypeptides arranged in a biologically functional manner, often using coenzymes and cofactors such as ligands , or another protein or other macromolecule such as DNA or RNA , or complex macromolecular are bound by assemblies . Amino acids incorporated into peptides are called residues . A water molecule is released during the formation of each amide bond .  All peptides, except cyclic peptides , contain an N-terminal (amine group) and C-terminal (carboxyl group) residue at the end of the peptide (as shown for the tetrapeptide in the image).
Several types of peptides are known. They are classified or classified according to their sources and functions. According to the Handbook of Biologically Active Peptides, some of the groups of peptides include Plant Peptides, Bacterial/Antibiotic Peptides, Fungal Peptides, Invertebrate Peptides, Amphibian/Skin Peptides, Venom Peptides, Cancer/Anticancer Peptides, Vaccine Peptides, Immune/Inflammatory Peptides, brain is involved. Peptides, Endocrine Peptides, Ingestive Peptides, Gastrointestinal Peptides, Cardiovascular Peptides, Renal Peptides, Respiratory Peptides, Opiate Peptides, Neurotrophic Peptides and Blood-Brain Peptides. 
Some ribosomal peptides are subject to proteolysis. These functions, usually in higher organisms, are in the form of hormones and signaling molecules. Some organisms produce peptides as antibiotics, such as microkines and bacteriocins.
Peptides often have post-translational modifications such as phosphorylation, hydroxylation, sulfonation, palmitoylation, glycosylation and disulfide formation. In general, peptides are linear, although lariat structures have been observed.  There are more exotic manipulations, such as the racemization of L-amino acids into D-amino acids in the platypus venom. [11 1]
Nonribosomal peptides are assembled by enzymes, not ribosomes. A common non-ribosomal peptide is glutathione, a component of the antioxidant defenses of most aerobic organisms.  Other non-ribosomal peptides are most common in unicellular organisms, plants and fungi and are synthesized by modular enzyme complexes called nonribosomal peptide synthetases .
These complexes are often placed in a similar manner, and they may contain many different modules to perform a variety of chemical manipulations on the developing product.  These peptides are often cyclic and can have highly complex cyclic structures, although linear non-ribosomal peptides are also common. Since the system is closely related to the machinery for manufacturing fatty acids and polyketides, hybrid compounds are often found. The presence of oxazole or thiazole often indicates that the compound was synthesized in this way. 
Peptones are obtained from animal milk or meat digested by proteolysis.  In addition to small peptides, the resulting material includes fats, metals, salts, vitamins, and many other biological compounds. Peptones are used to grow bacteria and fungi in the nutrient medium. 
Peptide fragments refer to protein fragments that are used to identify or quantify the source protein.  These are often the product of enzymatic degradation performed in the laboratory on a controlled specimen, but may also be forensic or paleontological specimens that have been damaged by natural impacts.
Solid Phase Peptide Synthesis on a Rink Amide Resin Using Fmoc-α-Amine-protected Amino Acids
The peptide families in this segment are ribosomal peptides, usually with hormonal activity. All of these peptides are synthesized by cells as long “propeptides” or “proproteins” and are cut off before exiting the cell. They are released into the bloodstream where they perform their signaling functions.
- magnin family
- Cecropin family
- cathelicidin family
- defensin family
- substance drink
- neurokinin A
- neurokinin B
Vasoactive Intestinal Peptides
- VIP ( V asoactive Intestinal P peptide ; PHM27 )
- PACAP P ituitary A denylate C yclase Activating P eptide _
- Peptide PHI 27 ( P Peptide H Estidine I Solucene 27 )
- GHRH 1-24 ( G rowth H ormone R eleasing H ormone 1-24)
Pancreatic Polypeptide-Related Peptides
- NPY ( En Euro P eptide Y )
- p y y ( p eptide yy )
- APP ( A VIAN P ancreatic Polypeptide )
- PPY P ancreatic P ol Y Peptide
- Proopiomelanocortin (POMC) Peptides
- enkephalin pentapeptides
- Prodynorphin Peptides
- Aromatic short peptides
- Biomimetic Peptides
- Peptide amphiphiles
- Peptide Dendrimers
- B-type natriuretic peptide (BNP) – manufactured in the myocardium and useful in medical diagnostics
- Lactotripeptides – Lactotripeptides may reduce blood pressure,    although the evidence is mixed. 
- Peptidic constituents from the traditional Chinese medicine Cola cori asini in hematopoiesis. 
Many terms related to peptides have no strict length definition, and there is often overlap in their usage.
- A polypeptide is a single linear chain of several amino acids (of any length), held together by amide bonds.
- A protein consists of one or more polypeptides (approximately more than 50 amino acids long).
- An oligopeptide consists of only a few amino acids (between two and twenty).
number of amino acids
Peptides of defined length are named using IUPAC numerical multiplier prefixes.
- A monopeptide consists of one amino acid.
- A dipeptide consists of two amino acids.
- A tripeptide consists of three amino acids.
- A tetrapeptide has four amino acids.
- A pentapeptide consists of five amino acids.
- A hexapeptide has six amino acids.
- A heptapeptide consists of seven amino acids.
- An octapeptide consists of eight amino acids ( eg , angiotensin II).
- A nonpeptide consists of nine amino acids ( eg , oxytocin).
- A decapeptide consists of ten amino acids ( eg , gonadotropin-releasing hormone and angiotensin I).
- A neuropeptide is a peptide that is activated in association with nervous tissue.
- A lipopeptide is a peptide that has a lipid attached to it, and papdusins are lipopeptides that interact with GPCRs.
- A peptide hormone is a peptide that acts as a hormone.
- A proteose is a mixture of peptides produced by the hydrolysis of proteins. This word is a bit archaic.
- A peptidergic agent (or drug) is a chemical that acts by directly modifying peptide systems in the body or brain. An example is opioidergics, which are neuropeptidergics.
- A cell-penetrating peptide is a peptide capable of penetrating the cell membrane.
Frequently Asked Question
What is a polypeptide?
It is a linear organic polymer consisting of a large number of amino-acid residues bound together in a chain, forming part (or the whole) of a protein molecule (such as insulin). In short, a polypeptide is a peptide consisting of 2 or more amino acids.
What does a polypeptide chain consist of?
Polypeptide chains are formed by dehydration between the amino group of L-amino acid 4 and the carboxyl group of the other. One hundred or more amino acids are linked together with covalent peptide bonds at various specific sequences in the polypeptide chain in conjunction with the polypeptide chains to form a protein.
What is an example of a polypeptide?
The unique sequence of amino acids in the polypeptide chain is its primary structure. For example, the pancreatic hormone insulin consists of two polypeptide chains, A and B, and they are linked together by disulfide bonds.
What polymer are polypeptides made of?
Polypeptides (PPs) (proteins) are linear polymers of amino acids (HN-CHR-COOH), where R (bound to the central C) is a variable side chain (“residue”) – there are 20 different natural compounds.
What are the types of polymers?
Types or Classifications of Polymers -:
Natural Polymers:- Such polymers, which are obtained in natural state or directly by nature, are called natural polymers. ,
Synthetic polymers:- Such polymers which are manufactured by humans are called synthetic or synthetic polymers.