Educational Disclaimer
All articles and product information on this website are intended solely for educational and research purposes.
The compounds listed are designed exclusively for in vitro research (Latin: in glass), meaning experiments conducted outside the human or animal body.
These products:
- Are not pharmaceuticals
- Are not FDA-approved
- Must never be used to treat, prevent, or cure diseases
What Is a Peptide?
The word “peptide” comes from the Greek péssein, meaning “to digest.”
A peptide is a compound formed when amino acids are covalently linked via peptide bonds (–CO–NH–). These bonds form through dehydration condensation between the α-carboxyl group of one amino acid and the α-amino group of another.
Peptide Classification by Length
- Oligopeptides: 2–20 amino acids
- Polypeptides: 20–50 amino acids
- Proteins: >50 amino acids with defined three-dimensional structures
Peptides usually have molecular weights below 10 kDa, with primary structures as linear sequences of amino acids. Some may adopt secondary structures like α-helices or β-turns, enabling diverse biological roles in signal transduction, immune responses, and metabolic regulation.
How Are Peptides Formed?
1. Natural Formation (In Vivo)
- Occurs in ribosomes guided by mRNA templates
- tRNAs deliver amino acids to the ribosome
- Enzymatic catalysis forms peptide bonds via dehydration
- Produces oligopeptides and polypeptides in precise sequences
2. Non-Ribosomal Synthesis
- Catalyzed by specialized enzyme complexes (peptide synthetases)
- Common in microorganisms producing bioactive peptides like antibiotics
- Can incorporate non-natural amino acids
3. In Vitro Chemical Synthesis
- Primarily via Solid-Phase Peptide Synthesis (SPPS)
- Protected amino acids are sequentially attached to a resin support
- Deprotection and condensation extend the chain stepwise
- Useful for short peptides with precise sequences
Peptide bond formation is central to building the primary structure of peptides and proteins.
Peptide Nomenclature
Peptides are usually named according to the number of amino acids:
| Number of Amino Acids | Name Example |
|---|---|
| 2 | Dipeptide |
| 3 | Tripeptide |
| 10 | Decapeptide |
| >10 | 11-peptide, 20-peptide, etc. |
Special Cases
- Cyclic peptides: e.g., cyclosporine, gramicidin
- Modified peptides: e.g., D-amino acids in actinomycin
- Function-based naming: e.g., mellitin (antimicrobial), thyrotropin-releasing hormone (signaling)
Peptide Classification
Peptides can be classified in multiple ways:
1. By Amino Acid Count
- Oligopeptides (2–20): Highly active, e.g., glutathione
- Polypeptides (20–50): Form simple structures, e.g., insulin fragments
- Proteins (>50): Complex functions, e.g., insulin (51 amino acids)
2. By Structure
- Linear peptides: Linked by α-peptide bonds, e.g., enkephalins
- Cyclic peptides: Ring formation, e.g., cyclosporine
- Modified peptides: Contain unnatural components
- Special linkage peptides: e.g., γ-peptide bond in glutathione
3. By Synthesis
- Ribosomal peptides: Encoded by genes, e.g., insulin
- Non-ribosomal peptides: Microbial enzyme complexes, e.g., mycopeptides
- Synthetic peptides: Chemically or enzymatically prepared, e.g., octreotide
4. By Function
- Signaling peptides: e.g., thyrotropin-releasing hormone
- Antibacterial peptides: e.g., bee venom peptides
- Neuropeptides: e.g., endorphins for pain regulation
- Medicinal or functional food peptides
5. By Source
- Natural: Found in organisms or foods, e.g., casein peptides
- Synthetic: Artificially engineered for cosmetics, medicine, or research
6. By Biological Origin
- Animal: e.g., tensin
- Plant: e.g., soybean peptides
- Microbial: e.g., Mycobacterium peptides
Important Peptide-Related Terms
- Peptide bond: Covalent bond (–CO–NH–) linking amino acids
- Oligopeptide: 2–20 amino acids; highly biologically active
- Polypeptide: 20–50 amino acids; can form simple secondary structures
- Primary structure: Amino acid sequence; determines function
- Secondary structure: Local hydrogen-bonded structures (α-helix, β-sheet)
- Cyclic peptides: Peptides forming a ring; stable and resistant to degradation
- Ribosome-synthesized peptides: Encoded by genes, formed in cells
- Non-ribosomal peptides: Synthesized by microbial enzymes; may include D-amino acids
- Solid-Phase Peptide Synthesis (SPPS): Laboratory method for precise peptide assembly
Educational Disclaimer
All articles and product information on this website are intended solely for educational and research purposes.
The compounds listed are designed exclusively for in vitro research (Latin: in glass), meaning experiments conducted outside the human or animal body.
These products:
- Are not pharmaceuticals
- Are not FDA-approved
- Must never be used to treat, prevent, or cure diseases
What Is a Peptide?
The word “peptide” comes from the Greek péssein, meaning “to digest.”
A peptide is a compound formed when amino acids are covalently linked via peptide bonds (–CO–NH–). These bonds form through dehydration condensation between the α-carboxyl group of one amino acid and the α-amino group of another.
Peptide Classification by Length
- Oligopeptides: 2–20 amino acids
- Polypeptides: 20–50 amino acids
- Proteins: >50 amino acids with defined three-dimensional structures
Peptides usually have molecular weights below 10 kDa, with primary structures as linear sequences of amino acids. Some may adopt secondary structures like α-helices or β-turns, enabling diverse biological roles in signal transduction, immune responses, and metabolic regulation.
How Are Peptides Formed?
1. Natural Formation (In Vivo)
- Occurs in ribosomes guided by mRNA templates
- tRNAs deliver amino acids to the ribosome
- Enzymatic catalysis forms peptide bonds via dehydration
- Produces oligopeptides and polypeptides in precise sequences
2. Non-Ribosomal Synthesis
- Catalyzed by specialized enzyme complexes (peptide synthetases)
- Common in microorganisms producing bioactive peptides like antibiotics
- Can incorporate non-natural amino acids
3. In Vitro Chemical Synthesis
- Primarily via Solid-Phase Peptide Synthesis (SPPS)
- Protected amino acids are sequentially attached to a resin support
- Deprotection and condensation extend the chain stepwise
- Useful for short peptides with precise sequences
Peptide bond formation is central to building the primary structure of peptides and proteins.
Peptide Nomenclature
Peptides are usually named according to the number of amino acids:
| Number of Amino Acids | Name Example |
|---|---|
| 2 | Dipeptide |
| 3 | Tripeptide |
| 10 | Decapeptide |
| >10 | 11-peptide, 20-peptide, etc. |
Special Cases
- Cyclic peptides: e.g., cyclosporine, gramicidin
- Modified peptides: e.g., D-amino acids in actinomycin
- Function-based naming: e.g., mellitin (antimicrobial), thyrotropin-releasing hormone (signaling)
Peptide Classification
Peptides can be classified in multiple ways:
1. By Amino Acid Count
- Oligopeptides (2–20): Highly active, e.g., glutathione
- Polypeptides (20–50): Form simple structures, e.g., insulin fragments
- Proteins (>50): Complex functions, e.g., insulin (51 amino acids)
2. By Structure
- Linear peptides: Linked by α-peptide bonds, e.g., enkephalins
- Cyclic peptides: Ring formation, e.g., cyclosporine
- Modified peptides: Contain unnatural components
- Special linkage peptides: e.g., γ-peptide bond in glutathione
3. By Synthesis
- Ribosomal peptides: Encoded by genes, e.g., insulin
- Non-ribosomal peptides: Microbial enzyme complexes, e.g., mycopeptides
- Synthetic peptides: Chemically or enzymatically prepared, e.g., octreotide
4. By Function
- Signaling peptides: e.g., thyrotropin-releasing hormone
- Antibacterial peptides: e.g., bee venom peptides
- Neuropeptides: e.g., endorphins for pain regulation
- Medicinal or functional food peptides
5. By Source
- Natural: Found in organisms or foods, e.g., casein peptides
- Synthetic: Artificially engineered for cosmetics, medicine, or research
6. By Biological Origin
- Animal: e.g., tensin
- Plant: e.g., soybean peptides
- Microbial: e.g., Mycobacterium peptides
Important Peptide-Related Terms
- Peptide bond: Covalent bond (–CO–NH–) linking amino acids
- Oligopeptide: 2–20 amino acids; highly biologically active
- Polypeptide: 20–50 amino acids; can form simple secondary structures
- Primary structure: Amino acid sequence; determines function
- Secondary structure: Local hydrogen-bonded structures (α-helix, β-sheet)
- Cyclic peptides: Peptides forming a ring; stable and resistant to degradation
- Ribosome-synthesized peptides: Encoded by genes, formed in cells
- Non-ribosomal peptides: Synthesized by microbial enzymes; may include D-amino acids
- Solid-Phase Peptide Synthesis (SPPS): Laboratory method for precise peptide assembly
