2.2.5 carbohydrates 3: polysaccharides as structural units Flashcards

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1
Q

describe cellulose

A
  • found in plants
  • forms cell walls
  • tough, insoluble & fibrous
  • homopolysaccharide made of long chains (up to 15000) beta glucose molecules bonded together via condensation reactions forming glycosidic bonds
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2
Q

what are cellulose chains like

A

straight & lay side by side

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3
Q

describe structure of cellulose –> esp. bonding

A
  • hydrogen & hydroxyl groups on carbon 1 are inverted in beta glucose = every other beta glucose molecule is rotated 180 degrees
    ^^this & the beta 1-4 glycosidic bond prevent chain spiralling
  • hydrogen bonding between rotated alpha glucose molecules in each chain = strength
  • hydrogen bonding between rotated beta glucose molecules in diff. chains = additional strength –> hydroxyl group on C 2 sticks out
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4
Q

when are microfibrils formed

A

when 60 to 70 cellulose chains are bound together
- 10-30nm in diameter

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5
Q

what are macrofibrils

A

microfibrils bundled together
–> contains up to 400 microfibrils embedded in pectins to form plant cell walls

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6
Q

why is cellulose an excellent material for plant cell walls

A
  • macrofibrils/microfibrils have high tensile strength (glycosidic bonds & hydrogen bonds between chains)
  • macrofibrils run in all directions & criss-cross = strength
  • difficult to digest cellulose due to glycosidic bonds between glucose molecules (less easy to break)
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7
Q

why do the features of cellulose help a plant cell wall to do it’s job

A
  • plants do not have rigid skeleton & each cell needs strength to support plant
  • space between macrofibrils for water/mineral ions to pass on way in/out of cell = cell wall fully permeable
  • wall has high tensile strength = prevents bursting if turgid & supports plant –> turgid cells press against each other & supports cell –> wall protects cell membrane
  • macrofibril structure reinforced by other substances for extra support or to make walls waterproof eg. cutin & suberin (waxes)
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8
Q

name 2 other structural polysaccharides

A
  • bacterial cell walls
  • exoskeletons
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9
Q

describe bacterial cell walls

A
  • whole structure surrounding cell = peptidoglycan
    –> long polysaccharide chains lying in parallel, cross-linked by short peptide chains (made of amino acids)
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10
Q

describe exoskeletons

A
  • insect/crustacean exoskeletons made of chitin
    –> has an acetylamino group (not hydroxyl group) on carbon 2
    –> forms cross-links between long parallel chains of acetylglucosamine
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