A-Level Biology OCR A
Alpha Glucose Beta Form Glycosidic Bonds Structure Flipped
Starch forms from alpha-glucoses linked by alpha 1,4 (and alpha 1,6 for branching) bonds, allowing a helical structure. Cellulose forms from beta-glucoses linked by beta 1,4 bonds, where molecules flip 180 degrees, resulting in a linear structure with intermolecular hydrogen bonds.
El almidón se forma a partir de alfa-glucosas unidas por enlaces alfa 1,4 (y alfa 1,6 para ramificaciones), lo que permite una estructura helicoidal. La celulosa se forma a partir de beta-glucosas unidas por enlaces beta 1,4, donde las moléculas se voltean 180 grados, resultando en una estructura lineal y con enlaces de hidrógeno intermoleculares.
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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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A-Level Biology OCR A