Research and laboratory use only. Not for human consumption.
Understanding Peptides
An introduction to peptide science — from amino acids and molecular structure to synthesis, biological signalling, stability and modern research.
What are peptides?
Peptides are molecules composed of amino acids connected by chemical bonds known as peptide bonds. Amino acids are also the building blocks of proteins, meaning that peptides and proteins share the same basic biochemical foundation.
There is no single universally applied boundary separating a peptide from a protein. In practical scientific usage, peptides generally refer to comparatively short amino acid chains, while longer chains capable of adopting complex three-dimensional structures are usually described as proteins. 1
Despite their relatively small size, peptides can possess substantial biological activity. Naturally occurring peptides participate in signalling processes throughout living organisms and can act as hormones, neurotransmitters, growth factors and signalling molecules.
These properties have made peptides an important area of biochemical, pharmacological and pharmaceutical research. Modern peptide science now encompasses naturally occurring peptides, synthetic analogues and rationally designed peptide structures. 1,2
Four fundamental concepts
Understanding peptide research begins with the relationship between amino acids, sequence, structure and biological activity.
Amino Acids
Organic molecules containing characteristic amino and carboxyl functional groups. Different amino-acid side chains contribute different chemical properties.
Peptide Bonds
Covalent amide bonds connect one amino acid to the next, creating the backbone of the peptide chain.
Sequence
The precise order of amino acids is the primary structure of a peptide and strongly influences its physical and biological properties.
Structure
Interactions between amino-acid residues influence molecular shape, receptor recognition, stability and biological behaviour.
Amino acids and peptide sequence
Each amino acid contains a central carbon atom associated with an amino group, a carboxyl group, a hydrogen atom and a variable side chain commonly represented as the R group.
It is the chemical character of these side chains that distinguishes individual amino acids. Side chains may be hydrophobic, polar, acidic, basic, aromatic or possess other chemical characteristics.
When amino acids are arranged into a peptide, their order is referred to as the amino-acid sequence. Even a small change in sequence can alter molecular recognition, stability, conformation or biological activity.
Consequently, peptide sequence is one of the most fundamental pieces of information used to characterise a research peptide.
The peptide bond
Amino acids in peptides are connected through amide linkages known as peptide bonds. These bonds form between the carboxyl group of one amino acid and the amino group of another.
Repetition of this linkage produces the characteristic peptide backbone. Attached to that backbone are the individual amino-acid side chains that give each peptide its particular chemical characteristics.
The peptide bond is not completely free to rotate because of its electronic structure. This contributes to the conformational behaviour of peptide chains and ultimately influences molecular shape.
Peptides are structurally diverse
Linear Peptides
Amino acids form an open chain with defined N- and C-terminal ends.
Cyclic Peptides
The peptide chain forms a cyclic structure. Cyclisation is one strategy investigated for altering peptide conformation and stability.
Modified Peptides
Chemical modifications can be introduced to investigate changes in stability, receptor affinity, half-life or other molecular characteristics.
Conjugated Peptides
Peptides may be chemically linked to other molecular groups as part of research into targeting, delivery or pharmacokinetic behaviour.
Peptide Analogues
Analogues are designed by altering a natural peptide sequence or structure while retaining selected molecular properties.
Peptidomimetics
Molecules designed to reproduce important structural or functional characteristics of peptides while introducing alternative chemical features.
How can peptides interact with biological systems?
Many biologically active peptides function through selective molecular recognition. Depending on the peptide, this can involve receptors, enzymes, proteins or other molecular targets. High target affinity and specificity are among the properties that have driven interest in peptide-based drug discovery. 1,3
Molecular Structure
Amino-acid sequence and conformation determine important chemical and structural properties of the peptide.
Target Recognition
Molecular characteristics may permit selective interaction with a particular receptor or other biological target.
Binding
The peptide-target interaction may alter receptor activity or another molecular process.
Signalling
Target interaction may initiate, inhibit or modify downstream biochemical signalling pathways.
Areas of peptide research
Metabolic Signalling
Peptide research has contributed substantially to understanding hormonal signalling and metabolic regulation.
Neuroscience
Neuropeptides and peptide receptors are studied for their roles in neuronal signalling and communication.
Immunology
Peptides participate in immune signalling, host defence and molecular recognition.
Endocrine Biology
Numerous hormones are peptides, making endocrine signalling a foundational area of peptide research.
Cellular Biology
Peptides are used experimentally to investigate receptor signalling, protein interactions and cellular pathways.
Drug Discovery
Peptide scaffolds and analogues are investigated as potential therapeutic candidates across multiple areas of medicine. 2,3
How synthetic peptides are produced
Modern peptide science uses several production approaches, including chemical synthesis and recombinant biological techniques. Advances in synthesis have been central to the development of peptide research. 2
Sequence Design
The required amino-acid sequence and any intended structural modifications are defined.
Chain Assembly
In solid-phase peptide synthesis, amino-acid residues are added sequentially while the growing peptide remains attached to a solid support.
Cleavage
Following chain assembly, the peptide is separated from the solid support and protecting groups are removed as required.
Purification
Analytical and preparative techniques can be used to separate the target peptide from synthesis-related impurities.
Characterisation
Analytical methods are used to investigate molecular identity, purity and other characteristics of the resulting peptide.
Why peptide stability matters
Stability is an important consideration in peptide science because peptides can undergo physical or chemical degradation.
The stability of any specific peptide depends on its sequence, structure, formulation and environmental conditions. Consequently, storage requirements cannot safely be generalised from one peptide to every other peptide.
Lyophilisation, or freeze-drying, is widely used in pharmaceutical and biochemical research to improve the storage stability of otherwise unstable biomolecules. 4
Why peptide development can be difficult
Metabolic Stability
Many natural peptides can be rapidly degraded by proteolytic enzymes, limiting their persistence in biological systems.
Membrane Permeability
Many peptides have limited ability to cross cellular membranes, restricting access to intracellular targets. 1
Delivery
Molecular size, enzymatic degradation and membrane permeability create substantial challenges for peptide delivery.
Pharmacokinetics
Researchers frequently investigate structural modifications designed to alter peptide half-life, distribution and stability. 2,3
Research compounds and approved medicines are not the same
Research Peptides
A peptide may be investigated in laboratory, animal, preclinical or clinical research without having received regulatory approval as a medicine. Experimental findings should therefore not automatically be interpreted as demonstrating safety or efficacy in humans.
Approved Peptide Medicines
Some peptide-based compounds have progressed through formal clinical development and regulatory review and are established medicines for defined indications. The success of approved peptide medicines does not establish the safety or effectiveness of unrelated experimental peptides. 1,2
References & further reading
The scientific overview on this page has been prepared with reference to peer-reviewed literature. References are provided for scientific context and are displayed without external links.
Scientific information notice
This page is provided for educational and research information purposes. Discussion of a peptide, biological mechanism, experimental study or area of scientific investigation does not imply that a compound is approved for medical use or that safety or efficacy has been established in humans. Information provided by ASA Research Labs should not be interpreted as medical advice, diagnosis, treatment guidance or clinical instruction.