Question

1. Sedoheptulose-7-P is a seven-carbon ketose intermediate in both the Calvin-Benson cycle and the oxidative pentose phosphate cycle. In both cases, the cycles are used to interconvert sugars using aldolases, transaldolases and/or transketolases; that is, in the CB cycle five trioses are converted into three pentoses, and in the OPP cycle three pentoses are converted into two hexoses and a triose. Using your knowledge of how aldolases, transaldolases and transketolases function to shuttle carbon between sugars, explain the importance of sedoheptulose-7-P in these two pathways. (3 marks)

Answer 1

Sedoheptulose-1,7-bisphosphatase (SBPase) is an important enzyme which catalyzes the dephosphorylation of sedoheptulose-1,7-bisphosphate to sedoheptulose-7-phosphate, with the regeneration of CO2 acceptor molecule RuBP in the Calvin Benson cycle.

The significant impact on the activity of SBPase is regulated by a variety of factors,like pH and Mg2+.. .

SBPase is activated through ferredoxin/thioredoxin system in response to the light.. ..

SBPase is an important enzyme in the regulation of photosynthetic carbon fixation in the Calvin-Benson cycle . ..

In case of pentose pathway cycle, sedoheptulose - 7- phosphate happens in non- oxidative phase. ..

It is ubiquitous, it produces sugars. .

It is inhibited by acidic conditions.. .