BIOSYNTHESIS OF SUCROSE IN PLANTSN BACTERIA

BIOCHEMISTRY

1. BIOSYNTHESIS OF SUCROSE
BY
Anju V Narayanan

2. •Sucroseiscommonsugar
•Itisadisaccharide,amoleculecomposedoftwomonosaccharides:glucose
•andfructose
•Sucroseisformedbyplants,algaeandcyanobacteriabutnotbyother
organisms
•Itisfoundnaturallyinmanyfoodplantsalongwiththemonosaccharide
fructose
•Inmanyfruits,suchaspineappleandapricot,sucroseisthemainsugar
•Inothers,suchasgrapesandpears,fructoseisthemainsugar
•Plantsusesucroseasastoragemolecule
•Forquickenergy,cellsmaystorethesugarforlateruse
SUCROSE

3. •Sucroseisformedbythecondensationpolymerizationofone
moleculeofglucoseandonemoleculeoffructosethrough
glycosidiclinkage
•Thelinkageisformedbetweenthecarbonofthealdehydegroupof
theglucoseandthecarbonoftheketonegroupofthefructose
•Glucoseexistspredominantlyasamixtureofαandβ"pyranose"
isomers,butonlytheαformlinkstofructose
•Fructoseitselfexistsasamixtureofαandβ"furanose"isomers,
butonlytheβisomerlinkstoglucose
SUCROSE STRUCTURE

4. SUCROSE STRUCTURE

5. •Thebiosynthesisofsucroseoccursinthecytosol
•ThebiosynthesisofsucroseproceedsviatheprecursorsUDP-
glucoseandfructose6-phosphate,catalyzedbytheenzymesucrose6-
phosphatesynthaseandtheconversionofsucrose6-phosphateto
sucrosecatalyzedbytheenzymesucrose6-phosphatephosphatase
•Theenergyforthereactionisgainedbythecleavageofuridine
diphosphate(UDP)
Continue…..

6. BIOSYNTHESISOF SUCROSE
•Photosynthesiscarriedoutbyplants,algaeandcyanobacteriaisthemajor
sourceoffixedcarbonforalllifeonearth
•Inplantphotosynthesis,carbondioxideisfixedinthechloroplastsviathe
Calvincycletoyieldtriosephosphates(triose-P)
•Triose-Pcanbetransportedtothecytosolbyatriose-P/phosphate
translocator
•Inthecytosol,twotriose-Pmolecules(Glyceraldehyde3-phosphateand
dihydroxyacetonephosphate)produceonefructose1,6-bisphosphate
(F1,6BP)moleculeinareactioncatalyzedbyaldolase
•F1,6BPisthenfurthermetabolizedtoyieldotherhexosephosphates,such
asfructose6-phophate(F6P)andglucose6-phosphate(G6P)

7. •Glucose 6-phosphate transforms to glucose 1-phosphate with the help of
enzyme, phosphoglucomutase
•Glucose 1-phosphate can be used to form UDP-glucose (UDP-G)
•Enzyme involved in this reaction is UDP-glucose pyrophosphorylase
•The pyrophosphate produced in the reaction is removed by pyrophosphatase
(2 Pi)
•UDP-G is combined with F6P to form sucrose 6-phosphate (sucrose-P) in a
reaction catalyzed by sucrose 6-phosphate synthase
•Sucrose 6-phosphate is dephosphorylated by sucrose 6-phosphate
phosphatase to form sucrose
Continue…..

8. 2 Pi
Pyrophosphatase

9. THANK YOU