Cellulose: Difference between revisions
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==Structure== | ==Structure== | ||
<StructureSection load='' size=' | <StructureSection load='' size='489' side='right' scene='82/824000/Cellobiose/4'> | ||
Glucose, the building block of cellulose and starch, can form six-membered rings with two distinct stereoisomers called the alpha and beta anomer. The only difference between alpha and beta glucose is at carbon C1. The [[disaccharides|disaccharide]] cellobiose (reload <scene name='82/824000/Cellobiose/4'>initial scene</scene>) is a breakdown product of cellulose which shows the beta 1,4 linkage between two glucose molecules also present in cellulose. "beta 1,4" refers to a glycosidic link between the anomeric carbon (<jmol><jmolLink><script> select 823.C1; selectionHalos ON; delay 0.5;selectionHalos OFF;</script><text>☼</text></jmolLink> </jmol>) in beta configuration of one glucose molecule with carbon 4 (<jmol><jmolLink><script> select 823.C4'; selectionHalos ON; delay 0.5;selectionHalos OFF;</script><text>☼</text></jmolLink> </jmol>) of the other glucose molecule. In contrast, starches (specifically the linear form amylose) can be broken down to [[disaccharides|maltose]], a stereoisomer of cellobiose showing an alpha 1,4 linkage. Thus, it is the type of glycosidic linkage that distinguishes cellulose from starches at the molecular level. | Glucose, the building block of cellulose and starch, can form six-membered rings with two distinct stereoisomers called the alpha and beta anomer. The only difference between alpha and beta glucose is at carbon C1. The [[disaccharides|disaccharide]] cellobiose (reload <scene name='82/824000/Cellobiose/4'>initial scene</scene>) is a breakdown product of cellulose which shows the beta 1,4 linkage between two glucose molecules also present in cellulose. "beta 1,4" refers to a glycosidic link between the anomeric carbon (<jmol><jmolLink><script> spin off; select 823.C1; selectionHalos ON; delay 0.5;selectionHalos OFF;</script><text>☼</text></jmolLink> </jmol>) in beta configuration of one glucose molecule with carbon 4 (<jmol><jmolLink><script> select 823.C4'; selectionHalos ON; delay 0.5;selectionHalos OFF;</script><text>☼</text></jmolLink> </jmol>) of the other glucose molecule. In contrast, starches (specifically the linear form [[amylose]]) can be broken down to [[disaccharides|maltose]], a stereoisomer of cellobiose showing an alpha 1,4 linkage. Thus, it is the type of glycosidic linkage that distinguishes cellulose from starches at the molecular level. | ||
Longer chains of beta 1,4 linked glucoses are found in cellulose. When cellulose is synthesized, these chains are made individually (cellulose chain during <scene name='82/824000/Cellulose/2'>biosynthesis</scene>). Again, the linkages are all of the beta 1,4 type (<jmol><jmolLink><script> select *.C1; selectionHalos ON; delay 0.5;selectionHalos OFF;</script><text>☼</text></jmolLink> </jmol>). In this structure, monomers are added to polymer chain inside the cell and secreted through the membrane, surrounded by the <scene name='82/824000/Cellulose/4'>enzyme</scene> throughout. | Longer chains of beta 1,4 linked glucoses are found in cellulose. When cellulose is synthesized, these chains are made individually (cellulose chain during <scene name='82/824000/Cellulose/2'>biosynthesis</scene>)<ref>DOI:10.1098/rsta.2017.0048</ref>. Again, the linkages are all of the beta 1,4 type (<jmol><jmolLink><script> select BGC and *.C1; selectionHalos ON; delay 0.5;selectionHalos OFF;</script><text>☼</text></jmolLink> </jmol>). In this structure, monomers are added to polymer chain inside the cell and secreted through the membrane, surrounded by the <scene name='82/824000/Cellulose/4'>enzyme</scene> throughout. | ||
Once secreted, individual cellulose chains self-assemble to from semi-crystalline cellulose | Once secreted, individual cellulose chains self-assemble to from semi-crystalline cellulose microfibrils. There are multiple forms of cellulose (I alpha and beta, II, III) which differ in the orientation and the detailed interactions between linear polymers. A model of a <scene name='82/824000/Microfibril/4'>cellulose type I beta micro-fibril</scene> shows a tightly packed structure. The model was made using cellulose builder (http://cces-sw.iqm.unicamp.br/cces/admin/cellulose, <ref>DOI:10.1002/jcc.22959</ref>) and is based on a fiber-diffraction study by Nishiyama et al <ref>DOI:10.1021/ja0257319</ref>. The <scene name='82/824000/Microfibril1d/1'>individual chains</scene> of cellulose form <scene name='82/824000/Microfibril2d/1'>layers</scene>, and multiple layers stack to form a <scene name='82/824000/Microfibril3d/1'>3D structure</scene> without any gaps. While interactions within layers are dominated by hydrogen bonding, <scene name='82/824000/Hydrophobic/1'>interactions between layers</scene> are hydrophobic<ref>DOI:10.1007/s10570-021-04325-4</ref>. You can use the buttons below to explore the 1D, 2D and 3D assembly of the microfibril model. | ||
Repeating unit | |||
Style <jmol> | |||
<jmolRadioGroup> | |||
<item> | |||
<script>select (4-5 and chain=M);spacefill only</script> | |||
<text>spacefill</text> | |||
</item> | |||
<item> | |||
<script>select (4-5 and chain=M);set bondmode OR; wireframe only</script> | |||
<text>bonds</text> | |||
</item> | |||
<item> | |||
<script>select 4-5 and chain=M;set bondmode OR; wireframe only; wireframe 0.2; spacefill 0.5</script> | |||
<text>ball-and-stick</text> | |||
<checked>true</checked> | |||
</item> | |||
</jmolRadioGroup> | |||
</jmol> | |||
Color <jmol> | |||
<jmolRadioGroup> | |||
<item> | |||
<script>select (4-5 and chain=M); color chain</script> | |||
<text>by chain</text> | |||
</item> | |||
<item> | |||
<script>select (4-5 and chain=M); color cpk</script> | |||
<text>by atomtype</text> | |||
</item> | |||
<item> | |||
<script>select (4-5 and chain=M); color black</script> | |||
<text>black</text> | |||
<checked>true</checked> | |||
</item> | |||
</jmolRadioGroup> | |||
</jmol> | |||
Rest of microfibril | |||
Show <jmol> | |||
<jmolRadioGroup> | |||
<item> | |||
<script>display chain=M and 4-5</script> | |||
<text>none</text> | |||
</item> | |||
<item> | |||
<script>display chain=M</script> | |||
<text>1D</text> | |||
</item> | |||
<item> | |||
<script>display chain=B or chain=G or chain=M or chain=R</script> | |||
<text>2D</text> | |||
</item> | |||
<item> | |||
<script>display all</script> | |||
<text>3D</text> | |||
<checked>true</checked> | |||
</item> | |||
</jmolRadioGroup> | |||
</jmol> | |||
Style <jmol> | |||
<jmolRadioGroup> | |||
<item> | |||
<script>select not (4-5 and chain=M);spacefill only</script> | |||
<text>spacefill</text> | |||
</item> | |||
<item> | |||
<script>select not (4-5 and chain=M);wireframe only</script> | |||
<text>bonds</text> | |||
</item> | |||
<item> | |||
<script>select not (4-5 and chain=M);wireframe only; wireframe 0.2; spacefill 20%</script> | |||
<text>ball-and-stick</text> | |||
<checked>true</checked> | |||
</item> | |||
</jmolRadioGroup> | |||
</jmol> | |||
Color <jmol> | |||
<jmolRadioGroup> | |||
<item> | |||
<script>select not (4-5 and chain=M); color chain</script> | |||
<text>by chain</text> | |||
</item> | |||
<item> | |||
<script>select not (4-5 and chain=M); color cpk</script> | |||
<text>by atomtype</text> | |||
</item> | |||
<item> | |||
<script>select not (4-5 and chain=M); color black</script> | |||
<text>black</text> | |||
<checked>true</checked> | |||
</item> | |||
</jmolRadioGroup> | |||
</jmol> | |||
<jmol> | |||
<jmolCheckbox> | |||
<scriptWhenUnChecked>hbond off | |||
</scriptWhenUnChecked> | |||
<scriptWhenchecked>select all; hbond on | |||
</scriptWhenchecked> | |||
<checked>false</checked> | |||
<text>hydrogen bonds</text> | |||
</jmolCheckbox> | |||
</jmol> | |||
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==See also== | ==See also== | ||
Lecture slides by Eero Kontturi, Aalto University, Espoo, Finland: https://mycourses.aalto.fi/pluginfile.php/148341/mod_folder/content/0/Lecture%202%20-%20Cellulose%20structure.pdf?forcedownload=1 | |||
== References == | == References == | ||
<references/> | <references/> | ||