What is a Peptide?

A peptide is a biologically occurring chemical compound that consists of two or more amino acids connected via peptide bonds. A peptide bond is a covalent bond formed between two amino acids when a carboxyl group or C-terminus of one amino acid reacts with the amino group or N-terminus of another amino acid in a condensation molecule of water is released during this reaction. The resulting bond is the CO-NH bond which forms a peptide or amide molecule. In the same way, peptide bonds are amide bonds.

The word peptide comes from the Greek word meaning “to digest.” They are an important part of nature and biochemistry, and thousands of peptides occur naturally inside the human body and in animals. In addition to this, new peptides are being discovered and synthesized regularly in the laboratory as well. Indeed, this discovery and innovation in the study of peptides exhibit great promise for the future in the fields of pharmaceutical and health development.

How Are They Formed?

Peptides are formed both via natural processes within the body and via synthetic processes inside the laboratory. Some peptides are manufactured organically by our body, like ribosomal and nonribosomal peptides. Inside a laboratory, modern peptide synthesis processes can make a virtually boundless number of peptides using peptide synthesis techniques like solid-phase peptide synthesis or liquid phase peptide synthesis. Solid-phase peptide synthesis is the standard peptide synthesis process used today, while liquid phase peptide synthesis has some advantages.

Peptide Formation

Vincent du Vigneaud synthesized the first oxytocin, which is a polypeptide that was synthesized in 1953.

Classification of Peptides

Peptides are mostly divided into several classes. These classes vary on the basis of how the peptides are produced by themselves. For example, the translation of mRNA produces ribosomal peptides. Ribosomal peptides mostly work as hormones and signaling molecules in organisms. These can include calcitonin peptides, vasoactive intestinal peptides, pancreatic peptides, and tachykinin peptide opioid peptides. Some organisms produce antibiotics like microcins which are ribosomal peptides. Ribosomal peptides mostly undergo the process of proteolysis, which means the breakdown of proteins into smaller peptides or amino acids to reach the mature form.

On the contrary, peptide-specific enzymes produce nonribosomal peptides. The ribosome does not produce them. Nonribosomal peptides are mainly cyclic rather than linear, although many times, linear nonribosomal peptides can occur. Nonribosomal peptides can develop extremely intricate cyclic structures. Nonribosomal peptides frequently appear in plants, fungi, and single-celled organisms. Glutathione, which is a significant part of antioxidant defense mechanisms in aerobic organisms, is the most common nonribosomal peptide.

Milk proteins form peptides in organisms. They can be produced by an enzymatic breakdown by digestive enzymes or by the proteinases formed by lactobacilli during the fermentation of milk. In addition to this, peptones are peptides that are derived from animal milk or meat that have been digested by proteolytic digestion. Peptones are often used in the laboratory as nutrients for growing fungi and bacteria.

Moreover, peptide fragments are most commonly found as the products of enzymatic degradation, which is performed in the laboratory on a controlled sample. However, peptide fragments can also occur naturally as a result of degradation by natural effects.

Important Terminologies used for Peptides

Amino Acids – Peptides consist of amino acids. An amino acid is any molecule that consists of both amine and carboxyl functional groups.

A cyclic peptide is a peptide in which the amino acid sequence forms a ring structure instead of a straight chain. Examples of cyclic peptides are Melanotan-2 and Bremelanotide (PT-141).

Peptide Sequence – It is simply the order in which peptide bonds connect amino acid residues in the peptide.

A peptide bond is a covalent bond formed between two amino acids when a carboxyl group of one amino acid reacts with the amino group of another amino acid. This reaction is a condensation reaction, a reaction in which a molecule of water is released.

Peptide Mapping is a process that can be used to validate or discover the amino acid sequence of specific peptides or proteins.

Peptide Mimetics is a molecule that biologically mimics active ligands of hormones, enzyme substrates, cytokines, viruses, or other bio-molecules. Peptide mimetics can be a synthetically modified peptide, natural peptide, or other molecules that perform the required function.

Peptide Fingerprint – It is a chromatographic pattern of the peptide. A peptide fingerprint is produced by partially hydrolyzing the peptide, which breaks up the peptide into fragments, and these are then undergone the 2-D mapping process.

Peptide Library – It consists of a large number of peptides that have a systematic combination of amino acids. Solid-phase peptide synthesis is the most frequent peptide synthesis technique that is used to prepare peptide libraries.


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