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Peptide
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<p>Peptides are short chains of <a href="/facts/Amino_acid/WDxYwBny">amino acids</a> linked by <a href="/facts/Peptide_bond/3FeX8M6q">peptide bonds</a>. A polypeptide is a longer, continuous, unbranched peptide chain. Polypeptides that have a <a href="/facts/Molecular_mass/FWueGMed">molecular mass</a> of 10,000 <a href="/facts/Dalton_(unit)/IMATU3vf">Da</a> or more are called <a href="/facts/Protein/Jxmagu3E">proteins</a>. Chains of fewer than twenty amino acids are called <a href="/facts/Oligopeptide/rM2AHGNV">oligopeptides</a>, and include <a href="/facts/Dipeptide/VkTVAaSy">dipeptides</a>, <a href="/facts/Tripeptide/ECavzDKk">tripeptides</a>, and <a href="/facts/Tetrapeptide/CzKC4heM">tetrapeptides</a>. </p><p>Peptides fall under the broad chemical classes of <a href="/facts/Biopolymer/GaCwr4EY">biological polymers</a> and <a href="/facts/Oligomer/v7oDY8zu">oligomers</a>, alongside <a href="/facts/Nucleic_acid/2tTgcI0v">nucleic acids</a>, <a href="/facts/Oligosaccharide/5to180o3">oligosaccharides</a>, <a href="/facts/Polysaccharide/lqXq2cJU">polysaccharides</a>, and others. </p><p>Proteins consist of one or more polypeptides arranged in a biologically functional way, often bound to <a href="/facts/Ligand_(biochemistry)/44QLL4eU">ligands</a> such as <a href="/facts/Coenzyme/AGo0PCUU">coenzymes</a> and <a href="/facts/Cofactor_(biochemistry)/AGo0PCUU">cofactors</a>, to another protein or other <a href="/facts/Macromolecule/039ULSLg">macromolecule</a> such as <a href="/facts/DNA/nB89Iauz">DNA</a> or <a href="/facts/RNA/HxPeNfNj">RNA</a>, or to complex <a href="/facts/Macromolecular_assemblies/H6fnKcte">macromolecular assemblies</a>. </p><p>Amino acids that have been incorporated into peptides are termed <a href="/facts/Residue_(chemistry)/xE6sUTDa">residues</a>. A water molecule is released during formation of each <a href="/facts/Amide/C6kCzYEA">amide</a> bond. All peptides except <a href="/facts/Cyclic_peptide/wTgSkstK">cyclic peptides</a> have an <a href="/facts/N-terminus/yKYpuaBJ">N-terminal</a> (amine group) and <a href="/facts/C-terminus/ws4scHgT">C-terminal</a> (carboxyl group) residue at the end of the peptide (as shown for the tetrapeptide in the image). </p>