Peptides are organic molecules made up of amino acids connected by peptide bonds. Synthetic peptides are made outside of cells using solid-phase peptide synthesis. They are used for research purposes, such as verifying the structure of naturally occurring peptides, studying biologically active proteins, and developing new therapeutic techniques. Peptide synthesis is also used to generate peptide libraries for screening biological properties and as drug delivery systems.
Peptides are organic molecules in which multiple amino acids are connected by peptide bonds. Each amino acid has a different side chain. All amino acids are composed of an amino group, which is NH2, and a carboxylate group, which is COOH. When these groups react, they create a peptide bond. When chemically made outside the cell, the peptide is known as a synthetic peptide.
A dipeptide contains two amino acids and has one peptide bond, while a tripeptide has three amino acids and two peptide bonds. The convention is that chains of amino acids up to 50 amino acids are known as peptides, while those longer are known as proteins. The main difference in making a synthetic peptide is that the amino acids are added from the carboxylate groups onwards. In cells, ribosomes begin synthesizing peptides with the amino group.
The most common method of producing synthetic peptides is to use solid-phase peptide synthesis. This allows for the formation of a synthetic peptide that would not occur in nature, such as those containing non-natural amino acids. With this method, the peptide chains are immobilized on porous spheres. Amino acids are treated with Fmoc or Boc protecting groups to protect them from unwanted reactions.
Peptides undergo repeated rounds of coupling and deprotection. When unprotected, the solid-phase attached peptide has a free amino-terminal group that is coupled to a nitrogen-protected amino acid unit. So this unit is deprotected and can react further to attack another amino acid. Once the peptide is complete, it is cleaved from the resin and purified by reverse-phase HPLC. The process that produces a synthetic peptide can be outsourced to several companies.
Peptide synthesis is performed for a variety of research objectives. Some researchers want to verify that they have correctly determined the structure of naturally occurring peptides. Others perform structure/function studies on biologically active proteins and peptides. Such peptides include hormones and a number of toxins. Often synthetic peptides are used as probes to study the active parts of protein molecules.
Peptides are instrumental in mass spectrometry in helping to identify whether a researcher has isolated a particular protein. Each protein breaks down into a pattern of unique peptides that can be detected by mass spectrometry. The process of producing antibodies to proteins in animals has become much easier with the advent of peptide synthesis. There is no need to laboriously purify the protein and use it to generate antibodies. One can synthesize a peptide from a protein fragment and then use that peptide as a source of antibodies.
A particularly active research area on synthetic peptides concerns the development of new therapeutic techniques, such as new vaccines. Peptide synthesis is used to generate peptide libraries for screening of their biological properties. Cell-penetrating peptides have been developed that are capable of introducing various factors into cells, including peptides, proteins, and the building blocks of DNA. Such techniques have great potential as drug delivery systems.
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