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Alpha Glucose Beta Form Glycosidic Bonds Structure Flipped

Front Explain why alpha glucose link together to form starch whereas beta glucose link together to form cellulose.
Back Alpha glucose and starch:
  • Two alpha glucoses next to each other can an alpha 1,4 glycosidic bond 
  • Hydroxyl groups on C1 and on C4 on neighboring glucose are on the same side of the ring and therefore can react in condensation and bond together
  • They can even form alpha 1,6 glycosidic bonds because the molecules are not flipped resulting in amylopectin branching
  • The helical strucrture forms because of intramolecular hydrogen bonds between -OH of C3 and -OH of C2 in the next glucose unit
  • Conclusion: two alpha glucoses form alpha 1,4 glycosidic bonds which allow intramolecular hydrogen bonding, forming a helical structure - amylose and can form 1,6 glycosidic bond branches too - amylopectin


Beta glucose and cellulose:
  • Two beta glucoses next to each other cannot bond like alpha glucses can
  • Hydroxyl groups on C1 and C4 are on diff sides of the ring and therefore cannot react in condensation and bond - theyre too far away
  • This is why one glucose molecule must be flipped 180 degrees with regards to the other 
  • This forms a beta 1,4 glycosidic bond 
  • There is no helical structure because each beta glucose monomer is upside down with respect to its neighbor - linear structure
  • Conclusion: two beta glucoses must be flipped with respect to each other which allows for a beta 1,4 glycosidic bond, this means only intermolecular hydrogen bonds can form - molecule will have linear structure - cellulose

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