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). 

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

3. 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.

2. 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.

3. 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.  

4. 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.

5. 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

Conclusion

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.