Peptide

polypeptidepeptidespolypeptidespeptonepolypeptide chaindecapeptidepolypeptide chainsheptapeptidenonapeptideoctapeptide
Peptides (from Greek language πεπτός, peptós "digested"; derived from πέσσειν, péssein "to digest") are short chains of amino acids linked by peptide (amide) bonds.wikipedia
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Tripeptide

The simplest peptides are dipeptides, followed by tripeptides, tetrapeptides, etc. A polypeptide is a long, continuous, and unbranched peptide chain.
A tripeptide is a peptide derived from three amino acids joined by two or sometimes three peptide bonds.

Tetrapeptide

The simplest peptides are dipeptides, followed by tripeptides, tetrapeptides, etc. A polypeptide is a long, continuous, and unbranched peptide chain.
A tetrapeptide is a peptide, classified as an oligopeptide, since it only consists of four amino acids joined by peptide bonds.

Amino acid

amino acidsresiduesresidue
Peptides (from Greek language πεπτός, peptós "digested"; derived from πέσσειν, péssein "to digest") are short chains of amino acids linked by peptide (amide) bonds.
They include the 22 proteinogenic ("protein-building") amino acids, which combine into peptide chains ("polypeptides") to form the building-blocks of a vast array of proteins.

Protein

proteinsproteinaceousstructural proteins
Peptides are distinguished from proteins on the basis of size, and as an arbitrary benchmark can be understood to contain approximately 50 or fewer amino acids.
A linear chain of amino acid residues is called a polypeptide.

Amyloid beta

beta amyloidbeta-amyloidβ-amyloid
Finally, while aspects of the lab techniques applied to peptides versus polypeptides and proteins differ (e.g., the specifics of electrophoresis, chromatography, etc.), the size boundaries that distinguish peptides from polypeptides and proteins are not absolute: long peptides such as amyloid beta have been referred to as proteins, and smaller proteins like insulin have been considered peptides.
Amyloid beta (Aβ or Abeta) denotes peptides of 36–43 amino acids that are crucially involved in Alzheimer's disease as the main component of the amyloid plaques found in the brains of people with Alzheimer's disease.

Cyclic peptide

cyclic peptidescycliccyclic dipeptide
All peptides except cyclic peptides have an N-terminal (amine group) and C-terminal (carboxyl group) residue at the end of the peptide (as shown for the tetrapeptide in the image).
Cyclic peptides are polypeptide chains which contain a circular sequence of bonds.

Macromolecular assembly

macromolecular assembliesBiological Unitmacromolecular structures
Proteins consist of one or more polypeptides arranged in a biologically functional way, often bound to ligands such as coenzymes and cofactors, or to another protein or other macromolecule (DNA, RNA, etc.), or to complex macromolecular assemblies.
The term macromolecular assembly (MA) refers to massive chemical structures such as viruses and non-biologic nanoparticles, cellular organelles and membranes and ribosomes, etc. that are complex mixtures of polypeptide, polynucleotide, polysaccharide or other polymeric macromolecules.

Proteolysis

proteolyticprotein degradationpolyprotein
Some ribosomal peptides are subject to proteolysis.
Proteolysis is the breakdown of proteins into smaller polypeptides or amino acids.

N-terminus

N-terminalN terminusN-
All peptides except cyclic peptides have an N-terminal (amine group) and C-terminal (carboxyl group) residue at the end of the peptide (as shown for the tetrapeptide in the image).
The N-terminus (also known as the amino-terminus, NH 2 -terminus, N-terminal end or amine-terminus) is the start of a protein or polypeptide referring to the free amine group (-NH 2 ) located at the end of a polypeptide.

Polymer

polymershomopolymerpolymeric
Hence, peptides fall under the broad chemical classes of biological oligomers and polymers, alongside nucleic acids, oligosaccharides and polysaccharides, etc.
There are three main classes of biopolymers: polysaccharides, polypeptides, and polynucleotides.

C-terminus

C-terminalC-terminal domainC terminus
All peptides except cyclic peptides have an N-terminal (amine group) and C-terminal (carboxyl group) residue at the end of the peptide (as shown for the tetrapeptide in the image).
The C-terminus (also known as the carboxyl-terminus, carboxy-terminus, C-terminal tail, C-terminal end, or COOH-terminus) is the end of an amino acid chain (protein or polypeptide), terminated by a free carboxyl group (-COOH).

Nonribosomal peptide

nonribosomal peptide synthetasenonribosomal peptide synthetasesnon-ribosomal peptide synthesis
Nonribosomal peptides are assembled by enzymes, not the ribosome.
Nonribosomal peptides (NRP) are a class of peptide secondary metabolites, usually produced by microorganisms like bacteria and fungi.

Hormone

hormoneshormonalprohormone
These function, typically in higher organisms, as hormones and signaling molecules.

Substance P

SPsubstance P (SP)
Substance P (SP) is an undecapeptide (a peptide composed of a chain of 11 amino acid residues) member of the tachykinin neuropeptide family.

Cathelicidin

LL-37CAMPcathelicidin antimicrobial peptides
Cathelicidin antimicrobial peptides LL-37 and FALL-39 are polypeptides that are primarily stored in the lysosomes of macrophages and polymorphonuclear leukocytes (PMNs); in humans, the CAMP gene encodes the peptide precursor CAP-18, which is cleaved into the active forms LL-37 and FALL-39.

RNA

ribonucleic aciddsRNAdouble-stranded RNA
Proteins consist of one or more polypeptides arranged in a biologically functional way, often bound to ligands such as coenzymes and cofactors, or to another protein or other macromolecule (DNA, RNA, etc.), or to complex macromolecular assemblies.
Transfer RNA (tRNA) is a small RNA chain of about 80 nucleotides that transfers a specific amino acid to a growing polypeptide chain at the ribosomal site of protein synthesis during translation.

Eledoisin

Eledoisin is an undecapeptide of mollusk origin, belonging to the tachykinin family of neuropeptides.

Dipeptide

dipeptidesdipeptide bondglorin
The simplest peptides are dipeptides, followed by tripeptides, tetrapeptides, etc. A polypeptide is a long, continuous, and unbranched peptide chain.
Dipeptides are produced from polypeptides by the action of the hydrolase enzyme dipeptidyl peptidase.

Kassinin

Kassinin is a peptide derived from the Kassina frog.

Proopiomelanocortin

pro-opiomelanocortinPOMCPOMC neurons
Pro-opiomelanocortin (POMC) is a precursor polypeptide with 241 amino acid residues.

Platypus venom

venomcrural glanddeliver venom
More exotic manipulations do occur, such as racemization of L-amino acids to D-amino acids in platypus venom.
The crural gland produces a venom secretion containing at least nineteen peptides; superadded by non-nitrogenous components.

Pancreatic polypeptide

pancreatic peptidePPY
Pancreatic polypeptide (PP) is a polypeptide secreted by PP cells in the endocrine pancreas predominantly in the head of the pancreas.

Enkephalin

enkephalins[ D -Ala 2 , D -Leu 5 ]enkephalinenkephaline

Microcin

microcinsmicrocin J25microcin V
Some organisms produce peptides as antibiotics, such as microcins.
The peptide has a cyclized backbone and forms three cross-links between the sulphurs of Cys13, Cys7 and Cys4 and the alpha-positions of Phe22,Thr28 and Phe31.

Chromatography

liquid chromatographychromatographicstationary phase
Finally, while aspects of the lab techniques applied to peptides versus polypeptides and proteins differ (e.g., the specifics of electrophoresis, chromatography, etc.), the size boundaries that distinguish peptides from polypeptides and proteins are not absolute: long peptides such as amyloid beta have been referred to as proteins, and smaller proteins like insulin have been considered peptides.
Ion exchange chromatography uses a charged stationary phase to separate charged compounds including anions, cations, amino acids, peptides, and proteins.