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Last updated date: 22nd Mar 2024
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An Introduction to Peptide

The peptide is taken from the Greek word “Peptos,” which means digested. The word “Peptos” is in turn derived from the word “péssin,” which means to digest. 


Peptides are smaller versions of proteins. They are short strings (i.e., between two and fifty ) of amino acids that are linked by peptide bonds. 


However, chains of fewer than ten or fifteen amino acid bonds are called oligopeptides that including dipeptides, tripeptides, and tetrapeptides. Many of the peptides are known and they are classified as per their sources and functions. The higher classification of a peptide is a polymer, while a lower classification is a nonribosomal peptide.


This page discusses the classification of peptides, peptide structure, properties of peptide bonds along with well-known peptide examples.


Peptide Definition

Peptides are short strings of amino acids whereas amino acids are likewise the structure squares of proteins. Be that as it may, proteins contain an enormous line of amino acids. It implies that peptides are little sisters of proteins.


What Are Proteins?

Proteins are considered to be the most abundant organic molecules that are found in the living systems and are way too diverse in their structure and function than any of the other classes of macromolecules. This protein which is quite diverse and unique has a bond in its amino acid monomer. This bond is called the peptide bond. Wondering what the peptide bond is and how it is formed? Well here is all about Peptide - Meaning, Classification, Structure, Formation, and Properties via Vedantu with the help of which you can prepare for your exams and study well!


What is a Peptide?

A human body can easily absorb peptides than proteins because peptides are smaller and more split than proteins. 


Also, peptides can more easily penetrate the skin and intestines; this penetrating ability of peptides helps them to enter the bloodstream more quickly.


We can earn peptides from the source plant and animal sources of protein, the list is as follows:

  • Eggs

  • Milk

  • Meat

  • Fish and shellfish

  • Beans and lentils

  • Soya beans

  • Oats

  • Flaxseed

  • Hemp seeds

  • Wheat


Classification of Peptides

Peptides are classified into oligopeptides and polypeptides. The formation of either of these depends on the union of amino acids 4 amino acids).  Now, let’s classify their forms:

  1. Linear Peptides - These peptides have a free NH2 at one end and a free COOH at the other.

  2.  Branched Peptides - These peptides have the branching of one or several amino acids on a linear peptide chain. Also, branching takes place either by the ω-carboxylic group of dicarboxylic amino acid or by the ε-amino group of lysine.

  3.  Cyclic Peptides neither have N-terminal nor C-terminal.

  4. Semi-Cyclic Peptides  - These peptides have only one end. It means if they have  N-ter­minal end, the α-COOH of the last amino acid is linked with the ε-NH\[_{2}\] of an endopeptidase lysine. Conversely, when there is a C-terminal, the α-NH\[_{2}\] of the first amino acid is linked with the ω-COOH of an endopeptidase dicarboxylic amino acid.


Peptide Structure

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Types of Peptide Bonds

  1. Dipeptide - 2 amino acid units.

  2. Tripeptide - 3 amino acid units.

  3. Tetrapeptide- 4 amino acid units.

  4. Oligopeptide - at most 10 amino acid units.

  5. Polypeptide = greater than 10 amino acid units, at most 100 residues.

  6. Macro Peptides = made up of more than 100 amino acid units.


Properties of Peptide Bond

An amino acid fused in a peptide chain loses one H (of its NH2) and one Goodness (of its COOH), or just one of the two in the event that it is a terminal amino acid. This is called an amino acid "buildup"; it is assigned by adding the addition "yl" to the foundation of the name (examples: glycyl, seryl, tyrosyl, and so forth) 


The amino acid of the N-terminal end is demonstrated first and afterwards, following the others in their request for progression, all with the postfix "yl"; just the amino acid of the C-terminal end is assigned by its unaltered name. Examples: alanyl-valyl-phenylalanine-isoleucine. One may likewise utilize shortened forms and compose: Ala-Val-Phe-Ile.


Peptide Bond Characteristics

According to two scientists Linus Pauling and Robert Corey, the peptide bonds are right and planar. The peptide bond characteristics are:

  1. Peptide bonds are solid with fractional twofold bond characters: 

  • They are not broken by warming or high salt focus. 

  • They can be broken by presenting them to solid corrosive or base for quite a while at the raised temperature. Likewise by some particular compounds (stomach-related catalysts). 

  1. peptide bonds are inflexible and planar bonds along these lines balance out protein structure. 

  2. Peptide bond contains incomplete positive charge gatherings (polar hydrogen molecules of amino gatherings) and fractional negative charge gatherings (polar oxygen particles of carboxyl gatherings)


Bioactive Peptides

Some peptides are very beneficial for the human body and they all have individual properties depending on the sequence of amino acids. These peptides are bioactive peptides or biologically active peptides.


As per the Handbook of Biologically Active Peptides, some peptides examples are:

  • Plant peptides

  • Bacterial/antibiotic peptides

  • Fungal peptides

  • Invertebrate peptides

  • Amphibian/skin peptides

  • Venom peptides

  • Cancer/anticancer peptides

  • Vaccine peptides

  • Immune/inflammatory peptides

  • Brain peptides

  • Endocrine peptides

  • Ingestive peptides

  • Gastrointestinal peptides

  • Cardiovascular peptides

  • Renal peptides

  • Respiratory peptides

  • Opiate peptides

  • Neurotrophic peptides

  • Blood-brain peptides.


Some Customary Supplements are:

  1. Collagen Peptides - These peptides benefit skin health and reverse the effects of ageing.

  2. Creatine Peptides - These peptides help to build strength and muscle mass.


Bioactive Peptides Uses

People use bioactive peptides functions because of the following reasons:

  • Lowers high blood pressure

  • Kills microbes

  • Reduces inflammation

  • Prevents the formation of blood clots

  • Improves immune system

  • Act as antioxidants


Many athletics take peptides and peptide hormones to enhance athletic activity. However, a peptide called Follistain (it helps in increasing muscle growth) was recently banned by the World Anti-Doping Agency.


Peptide Functions

Some Known Peptides Functions Include the Following:

  1. Vasopressin 

Vasopressin regulates the amount of water present in the fluid space around cells (extracellular fluid) It performs this function by causing the kidneys to absorb water. 

Also, in high quantities, vasopressin functions as a vasoconstrictor, which means that it causes blood vessels to narrow, and as a result, blood pressure rises.

  1. Oxytocin 

Oxytocin hormone is produced by the pituitary gland (located in the brain). It is made up of nine amino acids. 

It causes the uterus to contract during childbirth. Additionally, it plays an important role in the milk ejection reflex during breastfeeding. Often, it is known as the "cuddle hormone" or the "love hormone" because it is liberated when people snuggle up together or bond socially.

  1. Defensins

Defensins are activated peptides in the immune system and are known to be antimicrobial. These peptides are well-known for the wound healing process.  

  1. Angiotensins

Angiotensin hormones are part of the renin-angiotensin system. These peptides are responsible for regulating blood pressure. Also, they spur the discharge of aldosterone from the cortex to enhance sodium retention by the kidneys.

  1. Hepcidin 

It is a peptide hormone involved in controlling the human body’s iron absorption rate. The measurement of its levels in the body helps in the anaemia diagnosis.


What is Dipeptide?

A dipeptide is made of amino acids plus residue. A dipeptide is a natural compound got from two amino acids. The constituent amino acids can be something very similar or unique. At the point when unique, two isomers of the dipeptide are conceivable, contingent upon the arrangement. 


A few dipeptides are physiologically significant, and some are both physiologically and economically critical. A notable dipeptide is an aspartame, a counterfeit sweetener.


Dipeptides are white solids. Many are undeniably more water-solvent than the parent amino acids. For instance, the dipeptide Ala-Gln has the dissolvability of 586 g/L more than 10 times the dissolvability of Gln (35 g/L). 


Dipeptides likewise can display various secure qualities, for example regarding hydrolysis. Gln doesn't withstand sanitization strategies, while this dipeptide does. Since dipeptides are inclined to hydrolysis, the high solvency is abused in mixtures, for example, to give sustenance.


Dipeptide Structure

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Synthetic Dipeptide Preparation

Dipeptides are created by coupling amino acids. The amino gathering on one amino corrosive is delivered non-nucleophilic (P in the below equation) and the carboxylic acid gathering in the second amino acid is deactivated as its methyl ester. The two adjusted amino acids are then consolidated within the sight of a coupling specialist, which works with the arrangement of the amide bond: 


\[RCH(NHP)CO_{2}H + R'CH(NH_{2})CO_{2}CH_{3} \rightarrow RCH(NHP)C(O)NH(CHR')CO_{2}CH_{3} + H_{2}O \]


Ensuing this coupling reaction, the amine securing group P and the ester is changed over to the free amine and carboxylic acid, respectively.


For some amino acids, the subordinate practical gatherings are secured. The buildup of the amine and the carboxylic acid to shape the peptide bond for the most part utilizes coupling specialists to initiate the carboxylic acid. 


The Bergmann azlactone peptide amalgamation is an exemplary natural combination for the arrangement of dipeptides.


Dipeptide BioSynthesis

Dipeptides are delivered from polypeptides by the activity of the hydrolase chemical dipeptidyl peptidase. Dietary proteins are processed into dipeptides and amino acids, and the dipeptides are assimilated more quickly than the amino acids on the grounds that their take-up includes a different system. Dipeptides enact G-cells found in the stomach to emit gastrin.


Dipeptide Examples

Some dipeptides with their peptide functions:

  1. Homoserine (N-(4-aminobutyryl)- L-histidine) is another dipeptide distinguished in the cerebrum and muscles of vertebrates. 

  2. Diphenylalanine is the most examined constructing block in peptide nanotechnology 

  3. Kyotorphin (L-tyrosyl-L-arginine) is a neuroactive dipeptide that assumes a part in torment guidelines in the mind. 

  4. Balentine

  5. JA JA (or ophidian) (beta-alanyl-N tau-methyl histidine) has been recognized in the muscles of a few types of warm-blooded animals (counting man), and the chicken. 

  6. Gloria (N-propionyl-γ-L-glutamyl-L-ornithine-δ-lac ethyl ester) is a chemotactic dipeptide for the ooze shape Polysphondylium violaceum. 

  7. (6−Bromo−8−en−tryptophan)−arginine) is a cyclic dipeptide from the marine wipe Geodia barretti. 

  8. Dialanine is usually utilized as a model in Sub-atomic elements.


Commercial Dipeptide Examples

Some Commercially Known Dipeptide Examples Along With Their Peptide Functions are:

  1. Aspartame (N-L-α-aspartyl-L-phenylalanine 1-methyl ester) - an artificial sweetener.

  2. Carnosine (beta-alanyl-L-histidine) and Anserine (beta-alanyl-N-methyl histidine)  - Highly concentrated peptides in muscle and brain tissues. They are included in sports medicine.

  3. Acetylcarnosine - cataract prevention

  4. Ala-Gln and Gly-Tyr - infusion

  5. Val-Tyr, antihypertensive



The above article includes all the important concepts of peptides such as their definition, uses functions and structure etc. Students will get all the necessary knowledge and information related to peptides after going through the whole article.

FAQs on Peptide

1. Explain Peptides in Brief.

Peptides are normally present in protein-rich food sources. It isn't necessary to intake peptide enhancements or utilize effective wellsprings of peptides. 

Be that as it may, a few groups may wish to utilize collagen peptides determined to hinder the maturing interaction. However, others may take creatine peptides for muscle growth and fortitude. 

There is as yet restricted proof to show that these items are successful, and substantially more exploration is important to evaluate their adequacy and wellbeing altogether. 

Investigation into peptides is in the beginning phases, and later on, researchers may find the medical advantages of various sorts of peptides. Up to that point, individuals should practice alert when taking any enhancement and examine the expected advantages and dangers with their primary care physician heretofore.

2. What is the Function of Carnosine?

Carnosine is a dipeptide and characteristic cancer prevention agent that is found in the heart, kidneys, gut, skin, mind, and muscles. 

Studies show that it very well may be helpful in the treatment of conditions like Alzheimer's illness, mind ischemia, chemical imbalance, Down disorder, Parkinson's infection, schistosomiasis, and epilepsy. It may likewise be useful in forestalling the development of waterfalls in the eyes.

3. Describe Peptide Bond.

A peptide bond is a planar, trans and unbending setup. It additionally shows a fractional twofold bond character. The coplanarity of the peptide bond indicates the reverberation or fractional sharing of two sets of electrons between the amide nitrogen and carbonyl oxygen. 

The Particles C, H, N, O of the peptide bond lie in a similar plane, similar to the hydrogen atom of the amide group and the oxygen molecule of the carboxyl gathering are trans to one another.

4. What are the types and classes of peptides that are present?

There are several types and classes of peptides that are present can be provided as follows:

  • Milk Peptides: These are formed when the digestive system breaks down a protein called Casein. These also arise through the proteinases that come from lactobacilli during the fermentation of milk.

  • Non-Ribosomal Peptides: These are the peptides that are composed of enzymes that are unique to each of the peptides that are formed. Glutathione is considered the most common non-ribosomal peptide.

  • Peptones: Peptones are produced during the proteolysis function that takes place in either the animal meat or milk. It is also sometimes formed by the proteolysis of vitamins, salts, metals, and fats.

  • Ribosomal Peptides: Produced by the translational process of mRNA these are peptides that are subjected to proteolysis in order to get their mature form. These are also produced as a part of antibiotics by small bacteria. 

  • Peptide Fragments: Those protein fragments that are used in the identification or quantification of the source of proteins are called peptide fragments.  

5. What are some of the best applications of peptides?

Some of the best applications of peptides can be provided as follows:

  • Aspartame: This is a sweetener that is the replacement of sugar and is in fact 200 times sweeter than actual sugar. As it does not have any calories in it, it is highly used for various diet food production.

  • Antimicrobial Treatment: Antimicrobial peptides play a vital role in helping the treatment of infected skin and those that have burned. These are very useful in various medical applications.

  • Anti-aging Cream: There are different types of peptides that are present in anti-aging creams that help the skin to remain young and fresh.

6. Why are peptides very important in molecular biology?

Peptides are of high importance in molecular biology as they help in the production of peptide antibodies that are quite essential in a lot of animals. Apart from this they are also helpful in the study of protein functioning, its structure and is also used in mass spectrometry to get the correct structure elucidation. These peptides play an important role in creating antibodies in mice or rabbits against a specific protein that is life-endangering. There is also the presence of peptide hormones which are just hormones that contain peptide bonds.

7. Do peptides have the presence of isoelectric points in them?

An isoelectric point is said to be the pH at which a particular molecule will carry no net charge which means that the total charge involved will be zero. This principle is of high importance for the zwitterionic molecules which are mostly seen in amino acids, proteins, and peptides. For an amino acid, the isoelectric point can hence be said to be the average of pKa of both amine and the carboxyl group that is present which forms the peptide bond.

8. How does peptide bond formation take place?

Vedantu provides a piece of detailed information regarding the formation of peptide bonds where the amine group from one of the amino acids reacts with the carboxyl group of another amino acid to form the peptide bond. This reaction also has the removal of water where the hydrogen ions are removed from the amines and the hydroxyl groups are removed from the carboxyl group. This leads to the bond formation seen in the amino acids. To know more about how the formation takes place in mechanism and how the denaturation takes place students can access the Vedantu NCERT Solutions for Chemistry.