Editing Polymer backbone (section)

===Proteins and peptides===
Proteins are characterized by [[Peptide bond|amide linkages]] (-N(H)-C(O)-) formed by the condensation of [[amino acid]]s. The sequence of the amino acids in the polypeptide backbone is known as the [[Protein primary structure|primary structure]] of the protein. Like almost all polymers, protein fold and twist, forming into the [[Protein secondary structure|secondary structure]], which is rigidified by [[hydrogen bonding]] between the [[Carbonyl group|carbonyl]] oxygens and amide hydrogens in the backbone, i.e. C=O---HN. Further interactions between residues of the individual amino acids form the protein's [[Protein tertiary structure|tertiary structure]]. For this reason, the primary structure of the amino acids in the polypeptide backbone is the map of the final structure of a protein, and it therefore indicates its biological function.<ref>{{cite book |vauthors=Berg JM, Tymoczko JL, Stryer L |chapter=3.2 Primary Structure: Amino Acids Are Linked by Peptide Bonds to Form Polypeptide Chains |chapter-url=https://www.ncbi.nlm.nih.gov/books/NBK22364/ |id=NBK22364 |title=Biochemistry |publisher=W.H. Freeman |edition=5th |year=2002 |isbn=0-7167-3051-0 |url=https://www.ncbi.nlm.nih.gov/books/NBK21154/}}</ref><ref name=Voet16 /> Spatial positions of backbone atoms can be reconstructed from the positions of alpha carbons using computational tools for the backbone reconstruction.<ref>{{Cite journal|last=Badaczewska-Dawid|first=Aleksandra E.|last2=Kolinski|first2=Andrzej|last3=Kmiecik|first3=Sebastian|title=Computational reconstruction of atomistic protein structures from coarse-grained models|journal=Computational and Structural Biotechnology Journal|volume=18|pages=162–176|doi=10.1016/j.csbj.2019.12.007|pmid=31969975|pmc=6961067|issn=2001-0370|year=2020}}</ref>
[[File:Sucrose condensation.svg|thumb|A simplified example of condensation showing the ''alpha'' and ''beta'' classification. [[Glucose]] and [[fructose]] form [[sucrose]]. The synthesis of glycogen in the body is driven by the enzyme [[glycogen synthase]] which uses a [[uridine diphosphate]] (UDP) leaving group.]]