Petptides are formed when 2 (dipeptides) or less than 100 (polypeptides) amino acid residues are linked through amide bonds usually called “peptide bonds”. The condensation reaction that stimulates the formation of peptides occurs naturally although they can be synthesized for medical purposes. This bonding between amino acid residues is formed when an adjacent amine group and a carboxyl group react to structure a peptide bond. Proteins which play an important role in the biochemical and physiological functions of living things are a result of complex amino acid residue bonding. The major difference between protein molecules and peptides lies in their molecular weight determined by the number of amino acid residues. The structure of a peptide molecule has 2 ends. The end with a free carboxyl group is known as the C-terminus while the other end with free amino group is known as the N-terminus. The C terminal end and the N terminal end are normally drawn on the right and the left sides respectively.

Peptide Sequencing & Analysis

The amino acid or peptide sequence is basically the order in which the residues in peptides are arranged in peptides or proteins. The process starts by first carrying out an analysis to determine the ratio of the amino acids present in the peptide. Sequencing peptides can be done in various ways and reporting is done from the N terminus to the C terminus. The peptide bonds have to be hydrolyzed using an acidic catalyst such as hydrochloric acid. Even a simple dipeptide has 2 possible sequences. If the analysis of a dipeptide results in 2 units ala and gly, the dipeptide could then be either ala-gly or gly-ala depending on which side is the N terminal end. To determine the exact amino acids occupying N terminus and the C terminus, a process known as Edman degradation is used. The major problem with Edman degradation is that it is not reliable when working on peptides with more than 30 units of amino acids. Repeating the process can only yield results for up to 5 amino acids in a peptide sequence. The properties of proteins and peptides depend on the way the peptide chains are folded, stretched or coiled in space as well as the component amino acids’ bonding sequence.Understanding these concepts allows us to synthesize peptides that can be used in various medical processes.

Peptides and Biological Functions

Multi-cellular organisms use opposing peptides as regulators for complex activities such as blood pressure and help maintain a stable internal environment through a process called homeostasis. In the case of blood pressure, 2 peptides ANF (Atrial Natriuretic Factor) and an anti-diuretic hormone called Vasopressin work together through a series of chemical reactions to balance the blood viscosity and volume effect. This is basically achieved by controlling the amount of water in the blood and inhibiting secretion of renin from the kidneys.

Another peptide, GSH (tripeptide glutathione) which is a very essential intracellular antioxidant is actively involved in the synthesis of DNA and protein molecules. Other important functions performed by glutathione in living organisms include cell protection from oxidation by reacting with peroxides (such as hydrogen peroxide), transporting amino acids and metabolizing environmental toxins and drugs.

Peptides and Evolutionary Genetics

The study of evolution in different species is largely based on the sequence homologies of Cytochrome c (a mitochondrial redox protein). Polypeptides have unique amino acid sequences and the interaction of amino acid residues determine the structure of proteins as well as the functional role or how they relate to other proteins. Homologous polypeptides have a common gene ancestry and similar amino acid sequences making them ideal for the tracing of genetic relationships in dissimilar species. Polypeptide amino acid sequences change over time due to the evolutionary process and these modifications are randomly caused by spontaneous DNA alterations commonly known as mutations. It is however important to note that the function of polypeptides is not affected by any changes to their primary sequence. A good example can be illustrated by the identical primary structure of “cytochrome c” data collected from chimpanzees and humans which are believed to have diverged 4 million years ago. Other species like sheep, kangaroos and whales that diverged 50 million years ago show a remarkable resemblance in their protein structure which differ from the human protein by just 10 amino acid residues.

This article was provided for educational purposes. Those interested in conducting medical research can buy peptides and other lab chemicals for an established dealer. Have fun, and come back for another post soon!